. Aquarium and Pond UV Sterilizer, Clarifier Reviews; Problems

UV Sterilizer Reviews; Information Articles, Ideas, Comments, and Links to even more Resources about how UVC Sterilization works in Aquariums/ Ponds

aquarium and pond UV posts, information, articles, resources, blogs

Information Articles (Posts), Ideas, Comments, & Links to even more Information about how UV (UVC) Sterilization works in Aquariums/ Ponds.
For a COMPLETE up to date article about aquarium and pond uv sterilization, please visit this site:
UV Sterilization in Aquariums and Ponds; How it works

For all Articles, from basic to advanced, such as UVC, Watts, mW/cm2, please scroll down the Right Side Bar of this site for easy links

High Output UVC Emission from a UV Bulb/Lamp; Aquarium or Pond


Last Updated: 3/9/2020

Bacteria Joke, Actual UVC Emissions from UV Bulb, Review

Actual UVC output from your Aquarium/Pond UV Bulb/Lamp

A great point was brought up in one of our blogs specify geared to sterilizers and UV bulbs.
All the time, we hear about the wattage a bulb of any kind uses.
A standard light we use in our homes are 60 watt bulbs.
In water sterilizers, the bulb might be a 30 watt bulb.

The point made and the question now being; does a 30 watt UV-C bulb emit 30 watts of useful sterilizing watts?
And, the answer is No.
The UV-C wattage emitted is not the same wattage of a lamp.

Wattage of a bulb can be misleading. Watts used in a bulb is the power consumption of a bulb.
A 60 watt bulb used 60 watts of power. The actual output of a bulb is directly related to the wattage.
The higher the watts used, the great the power consumption.
But what is noteworthy, is that the wattage though does not actually tell us how much useful output the bulb has, or how efficient it is.
The efficiency of the bulb is the actual output of the bulb.

This efficiency is what becomes important as we look for a replacement for our UV Sterilizer/Clarifier or even a new UV Sterilizer as most of what is sold via the Internet or discounter brick & mortar stores are LOW OUTPUT medium pressure UV bulbs/lamps with as little as 25% of the UVC of the vastly better low pressure high output UV lamps sold but by a handful of high end sellers.
So please read on and beware if the price seems too good.


Specify speaking about UV-C bulbs, they have a light energy spike at a certain wavelength of light (254nm). This light energy is what sterilizes.
With any UV-C bulb, there will be an energy spike at this lighting level as well use some of it lighting energy on other parts of the lighting spectrum.

The light emitted at the UV-C namometer of light is the useful energy or wattage used from the bulb. The other energy emitted on the lighting spectrum that is not UV-C is essentially wasted energy.
Therefore the wattage of the lamp is not the same wattage being emitted of UV-C.
A 30 watt UV bulb does not emit 30 watts of UV-C.

Take a look at this picture which shows the energy spike of a UV bulb. At this spike, light energy has sterilizing abilities.

UVC Emission from Aquarium or Pond UV Bulb, review

In a premium low pressure true UV bulb, the actual UV-C emission of the bulb is about 35%. If you have a 30 watt UV bulb, it will emit 10.5 watts of germicidal UV-C.
Nail curing UV Bulbs, are commonly sold on Amazon & eBay for aquarium pond use at a lower cost (generally for retails prices of $5 to $15).
These are usually medium pressure UV bulb with a low 7-10% output of useful UV-C irradiation. These lamps have a wholesale cost of only a few $ for the smallest ones.
What buyers should also be aware of is how many hours the lamp/bulb is rated to last as true HO low pressure UV lamps burn themselves up quickly with only 4000 hours at peak performance. So if the lamp advertises 8000-10,000 hours--- AVOID IT!

The fact remains, that a true High Output "low pressure mercury" UV lamp/bulb has a distributor cost of at least $10 for even the smallest/cheapest of lamps, so if it is selling for this cost you know you are NOT get what you need to best run your UV Sterilizer or even Clarifier

As well the Halogen UV bulbs sold in some mini UV Sterilizers also have little of the peak UVC irradiation, more in the UVB range (these too are sold at discounters such as Amazon, not quality professional UV Sterilizer sellers). A good example of a UV Clarifier sold with these UV lamps is the Cobalt Aquatics Micro-UV which besides using the lower output Halogen UV lamp/bulb, it has very poor dwell time.

Both of these types of these low cost UV bulbs are marginal for clarification at best, certainly NOT level one or higher UV Sterilization unless used at very high wattages per water flow!! When combined with the lower dwell time that most of these Sterilizers that utilize these medium pressure lamps have (generally compact UVs), you are looking 1/4 the killing/sterilization/clarification power!!
An example would be comparing a TMC Vecton 15 Watt to a Jebaeo 55 watt that is commonly supplied with medium pressure UV lamps/bulbs (15 x 4 = 60).

Actual UV Output in Lamps purchased from Amazon

As an example, if you have a 9 Watt UV Sterilizer (such as the Turbo Twist), and when the bulb is due for replacement you utilize one of the low cost medium pressure UV Bulbs, you will be getting 1/4 to 1/3 the output of a premium low pressure bulb. So if you have a flow rate of 200 gallons per hour on your say 50 gallon aquarium as would be a flow rate for low pressure UV Bulb, then switch to the low cost medium pressure UV Bulb, you would need a flow rate of 80 gph just to maintain Level One UV Sterilization.
The bottom line is to not be tempted by the low prices of the nail curing medium pressure UV Bulbs that many retailers either unknowingly or knowingly incorrectly market for pond or aquarium UV Sterilizer use!

Please Reference:
UV Sterilization; Basic Factors

Recommended Professional Source for Premium Low Pressure UV Bulbs:
*American Aquarium PREMIUM Low Pressure UV Bulbs; Compact Style
*American Aquarium PREMIUM Low Pressure UV Bulbs; Straight Tube Style (for Aqua Ultraviolet, TMC, more)

Normally, the actual emission of a UV bulb is something you will not need to worry about, but what you do what to make sure is you are getting a large enough sterilizer for the water quantity you are looking to sterilization.
Company’s that know what they are talking about will publish this information or keep it in mind, when giving recommendation.
If you are not sure, make sure to look for what kind of bulb/lamp the sterilizer has and how much UV-C you are actually getting.

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9 Watt UV Bulb; Aquarium & Pond Germicidal, Review


Updated 12-25-18

What's in a UVC Replacement Bulb?

If you have followed this blog/website for some time, you would know that ONLY a 254 nm HOT CATHODE LOW PRESSURE UV Bulb should EVER be used in your Aquarium UV Sterilizer, Pond UV Sterilizer/Clarifier, or Air UVC Purifier.

*Hot Cathode vs. Cold Cathode UV Bulb; Are these worth purchasing?
*Actual UV-C Emission from a UV Bulb; Aquarium or Pond

This is not to say that these higher output high quality UV Bulbs/Lamps are not easy to find, as they can be found. But not for prices much under $14-$15 and certainly not for $5.99 as some eBay sellers such as "Discount Aquatic" who have used ("copy & pasted") without permission information from premium UV bulb seller AAPs web page that implies their UV bulb is the same! BEWARE, a close observation shows the UV lamp/bulb these and other sellers is NOT THE SAME! Why spend the money on a UV Sterilizer only to put in a $5.99 blue light bulb??

Several manufacturers such as American Aquarium, Purely, & Phillips all sell ONLY hot cathode, low pressure 254 nm UV Bulbs that are also include the patented heat reducing technology or Norman lamps high efficiency, low heat/HO technology.

Supplier of these bulbs: American Aquarium Products; UV Bulbs

Please Read the full article to understand the difference between many of the 9 Watt UV Replacement Bulbs sold

Unfortunately though, MANY if not most of the low cost UV Bulbs sold on eBay (such as the Jebao Brand commonly sold on eBay), Amazon (under the brand 'AnyRay'), Nextag under brand names such as Ocious are NOT these same low pressure, hot cathode UV Bulbs intended for level one UVC Sterilization in pond or aquarium applications, RATHER these are medium pressure UV lamps INTENDED AS NAIL CURING LAMPS with a UV efficiency of only 7%!!
I am not necessarily accusing these sellers of fraud, rather most of these sellers find a source for the 'nail curing UV bulbs' and outwardly these look almost the same, but for a lower cost, so they see an opportunity to get a UV bulb for a lower price that they can in turn market at a lower price. Unfortunately most of these sellers would not know the difference between a low pressure UV bulb and a medium pressure UV bulb (again the later is only generally intended as a nail curing UV bulb).

See References:
UV Lamps, Bulb; How they work
Actual UV-C Emission from a UV Bulb; Aquarium or Pond

Actual UV Output in Lamps purchased from Amazon

Quite bluntly these medium pressure nail curing 9 watt UV bulbs at 7% germicidal UVC irradiation simply CANNOT destroy the bacteria or maintain aquatic Redox at any useful/normal flow rate when compared to the high UVC output hot cathode UV-C Bulbs!
A source for these bulbs:
True Level One, Low Pressure UV Bulbs for Aquarium or Pond Use

Now to the title of this article/review;
Those purchasing a replacement 9 Watt UV Bulb will find this UV lamp to be one of the most common UV Bulbs sold incorrectly as replacements when in fact many are not for aquarium, pond, purifier use, despite advertising to the contrary!

Many of these are simply are NOT going to do the job.
These cheap 9 Watt UV Bulbs (often sold for under $10) are only useful for nail curing or similar, NOT to attempt to maintain Level 1 Sterilization in your important Aquarium or Pond UV Sterilizer!

Please Reference: Aquarium/Pond UV Sterilization
A source for good to premium UV Sterilizers: UV Sterilizer!!

What is also noteworthy, although often difficult to find, is some 9 Watt G23UV Replacement Bulbs use patented methods to lower operating temperature which increases the efficiency and UVC output.
Such as:
  • Patented Heat Reducing Technology
  • Norman lamps super high efficiency HO/low heat UV Bulbs.

Put in simple terms this makes for:
  • Lower operating temperatures which in turn increases energy directed as UVC (which is why you have a UV light in the first place). This 5° C difference increases efficiency about 5% or more, adding to the 75% improvement of these low pressure UV lamps over common lower cost medium pressure UV lamps/bulbs sold at online discounters and home improvement warehouses.
  • Longer Life and higher output over the life of the lamp.
  • Easier starts, which new hot cathode UV lamps are often difficult to start initially.

Now look and see if your bargain Amazon, eBay, etc. UV Bulb has this heat reducing technology;
Likely not!

THE FACTS ARE; the direct wholesale cost in volume purchasing is more than $10 for TRUE Low Pressure, Hot Cathode UVC Replacement Bulb/Lamp, so how is some Vendor going to sell these for much under $14 and pay the eBay seller fees, Amazon Fees, etc. (often offering shipping at below actual cost too), and still make a profit??
Of course the simple answer, which is not rocket science, is THEY CANNOT! This is why it is impossible to get a CORRECT TRUE Low Pressure, Hot Cathode UVC Replacement Bulb/Lamp at the prices offered on many of these websites that advertise on Google, etc.


9 Watt UV-C Bulb Comparison, eBay, Jebao, etc versus quality lamp

Another UV bulb that commonly comes up in search and is sold as less expensive alternative is the 18 Watt UV bulb/Lamp which it too is often a low output medium pressure UV Bulb with less than 7% UVC output.
This is another instance one should be careful of picking the first UV Bulb that comes up in Google search and instead choose a true low pressure hot cathode.
See my article/review for this bulb here: 18 Watt UV Bulb Review
Or to purchase a true 18 watt uvc bulb; True level one UVC capable 18 Watt UV Bulb

Simply put do NOT let Google, Bing, Yahoo guide you to one of these many websites selling these mostly useless UV Bulbs that produce little UVC necessary for an effective UV Sterilizer or Purifier.
Spend a little more and purchase a American Aquarium, Purely, or Phillips 9 Watt Bulb, which often still only sell for $14 to $25 online.

American Aquarium Products hot cathode 9 Watt is sold near cost as a promotional item and is THE true hot cathode, low pressure 9 Watt UV Bulb to purchase for both quality & price!!
See: 9 Watt UV Bulb

Please also read this article:
UV Lamps, Bulbs; How they work, Coatings, more

The bottom line is while you can certainly get a good deal for a good UV-C lamp/bulb, the old axiom still applies "THAT YOU GET WHAT YOU PAY FOR"!!

Finally, if you are having issues with your UV Bulb or Ballast or you would like some more information to understand why most 9 Watt UV Bulbs now sold are sub par, PLEASE give the video below a full viewing:

UV Bulb Review, Troubleshooting Video

Please reference this unique, in depth, & researched article that is IMPERATIVE READING for anyone interested in moving from basic aquarium or pond keeping to more advanced aquarium or pond keeping:

UV-C Sterilization Use; Beginner to Advanced

If you are looking for the optimum, MOST EFFICIENT LED lighting for your aquarium, look no further than the 5 year warranted AAP AquaRay line of LED lights (beware of a parasite retailer selling out of their home that Google's poor search algorithm brings up), please follow this link if you want the genuine AAP AquaRay:
AquaRay LED Lighting

By Steven Wright with input from Carl Strohmeyer-PAMR

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Green Pond Water, UV Clarifier


Revised 3/2/19

Green Pond UV Clarifier or Sterilizer Use

Green or Clear Pond

Green or Clear Pond?
The picture above albeit two different ponds demonstrates what is clearly the more desirable pond.

There are many causes and cures to this problem, however the use of a correctly applied UV Sterilizer/Clarifier is the most simple and popular, of which the correct application is the focus of this article.

This includes Placement, Flow, & Turnover among other factors

First though, let me briefly explain the causes:

Green water is caused by the accumulation of millions of single cell, microscopic spores of green algae suspended in the water. These single cell algae have the ability to turn your originally clear pond into what looks like pea green soup.

The main causative agent to green pond water is the sun.
Sunlight while in itself is necessary and healthy for life (such as Redox), excessive exposure can and will cause algae problems. The result is what is referred to as an "algae bloom" is when single cell green algae reproduces at a fast rate, as a result of sunlight and nutrients in the water.
Outside of shade by both or either plants or overhead trellises, not much can be done about sunlight (although seasons have a major impact on sunlight since the winter sun does not have nearly the impact of the summer sun, especially in higher latitudes).

Nutrients are the other primary causative agent, which in itself can have many causes from high fish bio load, poor filtration, accumulation of decaying organic matters, etc.

Good and regular maintenance can control decomposition of waste, while adequate filtration, especially a Veggie/Bog Plant Filter can help greatly by reducing nitrates in the water.

Reference this article for further information:
Pond Veggie/Bog Plant Filters

Other methods of Green Pond Water Control are listed here:

Pond UV Sterilizer, Clarifier for green water
Often many basic methods still fail to control these algae blooms and this is where a UV Sterilizer (as well as UV Clarifiers) comes in.
See this website for good to premium pond TRUE UV Sterilizers: Pond & Aquarium UV Sterilizers

The key is flow, correct wattage as per flow, dwell time, pond turnover, & placement

with flow rate, this should be under 50 gallons per hour per watt of UVC for most Compact UVsand as low as 40 gph per watt for many low end Basic UV Clarifiers that utilize poor dwell time and low output medium pressure UV Bulbs.
With higher dwell time "True" UV Sterilizers this rate can be as high as 60-70 gallons per watt of output UV energy (a "True" UV Sterilizer is one that maintains level one UV Sterilization or higher versus the many low end units often sold on eBay, Amazon, etc. that are only capable of basic clarification).
It is noteworthy that generally straight tube designs have a higher dwell time.

Premium Level One UV Sterilizer Resource:
AAP/TMC Pond UV-C Sterilizer, Clarfifier

Turnover is sometimes tricky with pond as although it does not need to be high for Green Water control (Once per 2-3 hours), the shape of the pond and more often, flow patterns may not allow for coverage of the entire pond.

What I mean is unlike most aquariums which tend to have relatively even circulation; many ponds may have one zone that has good circulation and another that does not.
The result is an area of the pond with poor circulation, along with sunlight and nutrients resulting in these green water producing algae spores.
Please also reference this UV Sterilization article section dealing with flow rate and turnover:
Pond Green Water Flow Rate Table

You can test this with dyes or even relatively harmless aquatic products such as Methylene Blue
For more Kordon Products such as Methylene Blue please see:
Kordon Methylene Blue from AAP

The solution, especially of you have a pond shape with more than one interconnected pond, is separate pumps/filters with separate UV Sterilizers.
As well, the use of Veggie/Bog filter as mentioned earlier (especially in areas of constriction) can lower nutrients so that the UV Sterilizer does not work as hard.
I would add that even with ponds in more formal rectangle or similar shape, separate flow patterns may still yield best results.

If one UV (with proper flow/dwell time) is not sufficient, adding another immediately in-line can improve results. However I will still state from my experience two separate UVs will often yield better results than two in-line.

An example would be the use of one 30 Watt AAP/TMC PRO UV Pond Clarifier (which is one of the best if not the best) for a pond up to 7000 gallons run with a flow rate of 2100 gph. This is clearly at the edge of this UVs operation envelope and although it make work well with optimum conditions (including a Veggie Filter), under other conditions such as high bio loads and considerable direct sunlight the addition of a second UV either in parallel on another pump (recommended) or inline on the same pump.

Resource: 30 Watt AAP/TMC PRO Pond UV Clarifiers

TMC 110 Watt Professional Large Pond UV Sterilizer & clarifier for green waterAnother idea for larger ponds in particular, is the use of large professional hard plumbed UV Sterilizer where by the water is split to different locations after passing through the UV Sterilizer to provide more even circulation.
Of course a large UV Sterilizer can also be used on multiple lines for exceptionally large pond or ponds that have high sun exposure with marginal bio filtration (although I still recommend a Veggie/Bog filter for any pond, no matter how large, as a UV Sterilizer should not be your only algae/green water control tool).

Easily the most exceptional high capacity professional UV Sterilizer for "hard plumbing" into one's pond is the TMC 110 Watt Professional Large Pond UV Sterilizer. Quite bluntly in my 35 years of professional pond design and maintenance, I have never found a more efficient UV sterilizer AT ANY PRICE (often I have spent much more for lesser results).
Resource: TMC 110 Watt Professional Large Pond/Aquarium UV Sterilizer/Clarifier

Aqua UV versus TMC UV Sterilizer
VIDEO: Aqua Pond UV vs TMC AAP Pond UV Clarifier Sterilizer

A comparison of the two top large pond/aquarium-system UV Sterilizers and why the AAP/TMC comes out as the best when price and dwell time is considered

This is important too, you first want to remove as many dissolved waste particulates from the water as possible as these can and do block UVC irradiation, making your UV Sterilizer less effective.

See/Reference: UV Transmittance; Other Factors Affecting UVC Sterilization Pre-Filtration & Turbidity

This is done by pre-filtering the water prior to entering into the UV Sterilizer, even if by just small sponge filter, gravel rock filter, etc.
Adding highly porous volcanic rock around a pump, even if it already has a sponge pre-filter can GREATLY help in pre-filtration of your pond water prior to entering the UV Sterilizer. This not only allows for a more effective UV Sterilizer, but also iads in keeping your pump from clogging with debris or the pre-filter sponge from clogging quickly

Product Resource: Volcanic Rock for Pond or Aquarium

Pond UV Circulation

Another essential of placement is to make sure that the pickup of the water to the UV is not close to the return, so as to provide as best of over all circulation as possible.

One can also install two (or more) smaller "loops of water" with multiple UV Sterilizers for better circulation with larger or irregular shaped ponds.

See also:
Pond Care Information; UV Sterilizer Use

Finally as per choosing a UV sterilizer, I will admit my bias, if it was/is not already apparent, and that is for the TMC Advantage professional line of UV Sterilizers.

I have been in the business of professionally maintaining ponds and aquariums since 1978, specializing in UV-C Sterilization.
I have tested and used most every brand and type of UV Sterilizer, I have even built my own from scratch. As well I have used and tested many brands of UV Bulbs for these units from cold cathode to superior Hot Cathode UV Bulbs, finding these albeit more difficult to light due to requirement of a peak voltage ballast, but vastly higher UVC output resulting in better sterilization and clarification (95% for the hot cathode versus 25% UVC output for the cold cathode).

See these web pages for recommended resources based on my professional UV Sterilizer design and use experience dating back to 1978: *Premium Hot Cathode UV Bulbs
*AAP/TMC Advantage professional line of Pond UV Sterilizers

My point is I have found the construction of the TMC Advantage UVs very solid and durable with flow/dwell time patterns second to none including often higher priced Aqua, Emperor, and Laguna UVs.
Just as importantly, when replacement parts are needed, TMC makes most all part easily available and reasonably priced; which I cannot say is the same for most other popular UVs.
When compared to the Tetra, another higher priced UV, the Advantage has a vastly superior flow design and dwell time (no compact UV such as the Tetra can compete with a straight tube for dwell time based on real world tests)

For more on Dwell time, please reference:
UV Dwell Time Test

Then there are all the submersible UV's such as the AquaTop that while I have used them, with some success; these ultra low cost UV's simply do not hold up long term in a harsh pond environment and eventually fail. As well these UV's often cannot clear green water unless conditions are otherwise optimum.

In summary when choosing a true level 1 capable UV Sterilizer over a low cost UV Clarifier, one might ask why bother spend the extra when all that is desired is clarification??

The answer is simple; a True level 1 capable UV can clear water at much higher flow rates, much more quickly sometimes in hours where as a UV Clarifier will often require days for the exact same pond!!
As well, the level one capable UV will improve Redox, which improves fish & pond health, and aid in disease prevention; something a UV Clarifier CANNOT perform.
Finally, many true UV Sterilizers are simply better built, which means you will likely get many years of service versus just one or two which is common to many of the lower quality UV clarifiers, including some of the more over rated models such as the Turbo Twist.
Reference: Turbo Twist UV Review

Resources, Recommended Reading:


Please reference this very in depth & researched article that is an IMPORTANT READ for anyone interested in moving from basic pond keeping to more advanced pond keeping:

Pond UV Sterilizer Use Beginner to Advanced

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13 Watt UV Bulb; Replacement Lamp G23 or GX23

Incorrect 13 Watt UV Bulb Replacement Recommendations

This is a shorter post than many here at UV Sterilizer Reviews, so although the content is short, the reason for writing this review is the copious amounts of incorrect information here on the internet about the correct 13 Watt Compact UV Bulbs to use for many Aquarium and Pond UV-C devices.

Sadly many websites or UV Bulb Guides are incorrectly recommending the GX23 UV Replacement Bulb (such as the Purely PUVX213) for these UV Sterilizers:

GX 2 Clip UV bulb Base,PUVX213 The GX style UV Bulb has a two clip base (see the picture to the left)
This GX base will not fit these before mentioned UV Sterilizers without modifications that may damage either your UV Lamp or UV Sterilizer (or both)

G23 1 Clip UV bulb Base,fits Terminator, AquaTop, Submariner The correct UV Bulb is the G23/PLS 13 Watt pictured to the left.
This Compact UV Bulb base fits many older UV Sterilizers/Clarifers as well that have newer models that take the GX23 UV Bulb base such as the older Cyprio & Fish Mate UVs

G23 Replacement UV Lamps

If you need a correct UV Replacement Bulb Guide, I suggest this professionally written website:

UV Replacement Bulb Guide

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UV Sterilizer Questions/Myths Answered for Pond & Reef Aquarium


Updated 4-6-19

More UV Sterilizer Questions/Myths Answered

In this post I will answer two questions (or possibly “myths”) about the use of UV Sterilizer in Aquariums and Ponds based on email and phone questions I often get.

Myths versus facts in UV Sterilizer use, aquarium or pond
The questions are:

• Filter placement in relation to UV Sterilizer in ponds.
• Danger of UV Sterilizers to copepods in reef aquariums.

Another article on sterilization in ponds:
Pond Care Information


(1) Question: Is the UV best placed after or before a filter in a pond?

This question is myth based as there are valid reasons for both applications.
However based on my own use and controlled tests using UV Sterilizers with filters before, after, or not at all, the answer of using the UV Sterilizer after the filter is the better choice.

Let me explain further; when a UV Sterilizer/Clarifier is placed BEFORE a pond filter with no pre-filtration, you do catch “clumped” algae coming from the UV Sterilizer.
This is even more noteworthy when a UV is run a flow rate over 30-35 gph per watt as this higher flow rate will generally not kill algae outright, rather “clump” the algae where it will be expelled from the UV Sterilizer into the pond water column.
Otherwise, this "clumped algae" then it either falls to the bottom of the pond becoming part of the organic mulm/detritus and/or may be picked up by any existing pond pump and filter and removed.

This is the ONLY reason to place a filter after a UV Sterilizer in pond applications.

With previous paragraph in mind, the generally better way to utilize a filter with a UV Sterilizer is to place the filter prior to the UV Sterilizer.
The reason is that turbidity in the water will lower UV Sterilizer effectiveness, and sometimes (based on my tests) to levels that render the UV Sterilizer ineffective.
This often results in the misinformed comment that UV Sterilizers do not work (based on emails and phone calls).

Pre-filtering the water prior to entering the Ultraviolet Sterilizer improves the function of UV Sterilizer by trapping larger particulates, thus allowing more of the UVC irradiation to reach the algae that is causing green water (this also improves destruction of disease pathogens at lower flow rates in both aquariums and ponds).

High Output UV Lamps for aquarium, pond
The other reason for pre-filtration of pond water is I have often have had success in initial clarification of pond water with no pre-filtration, but over time (& sometimes only a few weeks), sludge will build up in the UV Sterilizer.
Often this sludge builds up in recesses around the UV Bulb or quartz sleeve, rendering the UV Sterilizer/Clarifier useless.
This does not mean that pre-filtration does not prevent sludge from building, as it does not, but it most definitely slows down the accumulation of sludge, as well the time it takes to buildup sludge in your pond UV Sterilizer depends on water turbidity, algae, bio load and obviously the quality of your pre-filter.

Where to get:
UV Bulbs; Premium High Efficiency (not the low output UV lamps commonly sold on Amazon or eBay)
Quartz Sleeves
Pond UV Sterilizers

I should note that having both a pre-filter and a post filter (such as a DIY Bio falls or similar filter that fits into the water return prior to re-entering the pond) would be an excellent combination.

(2) Question: Will a UV Sterilizer kill off my beneficial copepod & other crustaceans colonies in my reef tank?

Although not as common a question as the previous question, it still crops up from time to time and I have much harder time understanding why otherwise quite advanced reef keeper fall for what amounts to a UV Sterilizer myth.

As well, my controlled studies admittedly did not include exact counts of copepods with different levels of UV Sterilization, it did show that copepod colonies when properly established never diminished with UV Sterilizer use in reef tanks.
Study Reference:UV Sterilization Studies

There is simple explanation for this result; that is most copepods do not occupy the water column in a healthy colony.

What is a healthy colony?
This is a matter of opinion or experience, but from my perspective a healthy colony is “housed” in large piles of live rock crumbles where many fish such as Mandarin Gobies will seek them out.
As well if you are using a Refugium and want to be certain that all of the copepods/ crustaceans that spill out into the aquarium are not killed, then be sure your UV is on its own filter/pump and not returning water to the aquarium using the same return line as the Refugium.
Finally whenever you dose your aquarium with certain live products such as live planktonic algae or infusoria, you should turn off the UV sterilizer or use a timer that is tied to certain cycles or automatic dosing.

Ocean Clear Aquarium Filter My final comment to this amounts to another aquarium keeping myth.
That is I have had clients/customers that have stood by this myth describe or show me their filter system and I have seen (or had them describe) several of these filter systems that employ micron filters (such as the Ocean Clear) that can easily trap copepods in their micron filters much more effectively than a UV Sterilizer can kill copepods.
In particular adult copepods for which a UV Sterilizer would have to run well under 10 gph per watt to have any chance of destroying any “pods” that get caught in the sterilizer.

As well pre-filtration which should be used in any UV Sterilizer application will trap most adult copepods from entering the Sterilizer.
What makes me laugh here is that these same aquarists often had healthy copepod colonies with the use of these Micron Filters.
I would explain to them that if these filters did not destroy their “pod” colonies, a UV Sterilizer would not either!
I should note that I am not against the use of these micron filters; in fact I think are excellent compliments to other aquarium filters, live rock, and healthy deep sand beds.

Please see this article for more about UV Sterilization and how it works:

UV Sterilization

Recommended Reading:
Common Aquarium Keeping Myths
Common Aquarium Keeping Myths

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UVC, Watts, Microwatts


Revised: 1/2/18

UVC, Watts, Microwatts, Joules, & Light Penetration

This article/post is intended to give some basic understanding between the relationship of watts, microwatts, joules of UVC energy and how this translates to UV Sterilizer effectiveness.

Please keep in mind that the diagram in this article is based on air penetration, so some extrapolation is necessary for use in water applications (which is the primary intention of this article, although the principles apply to UVC air sterilization devices as well)
UVC Air Sterilization Devices

What is a Watt/Microwatt?

One Joule of energy = 1,000 milliWatt seconds = 1,000,000 microWatt seconds
One joule is the amount of energy required to perform the following actions:

• The work done by a force of one newton traveling through a distance of one meter (a newton is the unit of force equal to the amount of force required to accelerate a mass of one kilogram at a rate of one meter per second per second);
• The work required to move an electric charge of one coulomb* (the amount of electric charge transported by a current of 1 ampere in 1 second) through an electrical potential difference of one volt; or one coulomb volt, with the symbol C•V;
• The work done to produce power of one watt continuously for one second; or one watt second (compare kilowatt hour), with the symbol W•s. Thus a kilowatt hour is 3,600,000 joules or 3.6 megajoules;
• The kinetic energy of a 2 kg mass moving at a velocity of 1 m/s. The energy is linear in the mass but quadratic in the velocity, being given by E = ½mv²;
we measure UV-C intensity in Micro-Watts that strike one square centimeter of surface area.
Reference: What is a coulomb?


UVC Penetration;
A quote from an advanced sterilization article:
UV Sterilization; How a UV Sterilizer Works

"The emission or light intensity of a UVC germicidal light bulb is usually expressed in a term called "microwatts per square centimeter" (Mw/cm2). The maximum intensity provided by a single UV-C Bulb is at its surface.
So, if we calculate the surface area of the UVC lamp and only use that area which effectively emits UVC light rays, the effective area of UVC transmission will be established. Basic mathematics will show that the surface area of a cylindrical tube is ‘pie’ D L.

Next extrapolate this effective area of UVC transmission as having a screen with squares 1 centimeter in size. Each of these cm2 areas now, for measurement purposes, emits a UVC lamp intensity measured in microwatts, in other words; the term microwatts/cm2. UVC light intensity decreasingly varies as the distance from the UVC light increases.

Put more simply (a non scientific analogy); The amount of wattage will also increase penetration, as a higher watt UV-C bulb will generally have more Mw/cm2."

See this product link for high output Straight Tube UV Bulbs:
Premium HO Straight Tube UV Lamps

"In my own experiments I have used 15 watt and 25 watt UVC bulbs in exactly the same unit (both were 18”), if wattage were only considered there would be a 60% increase in effectiveness, however I only observed a about a 25% increase.
When I used a 30 Watt UVC bulb in a unit with over twice the exposure as the 15 Watt, the kill rate more than doubled. From my experience, if you increase wattage (and Mw/cm2) you need to also increase the volume of water to maximize the higher watt bulb.
Experiments can also be safely conducted with standard household light bulbs to correlate penetration. For this start with a 7 watt clear bulb (such as a Christmas bulb) and place varying thicknesses of paper/ cardboard in front of the bulb and measure when penetration stops. Continue this with higher and higher wattage bulbs."

UVC Intensity, UV Sterilizer The Diagram to the left can give a rough comparison of distance as per UVC energy as expressed by MW/cm2 in Air transmission.
The dose applied by an UV-C lamp installation is a function of the lamp output, the intensity factor, and time. As an equation; Intensity x Exposure time= microwatt seconds/cm2.

As an example, a 9 watt UVC lamp at one inch from the lamp is found by this formula:
9 x 127 = 1143 mW/cm2.
Since many bacteria such as Vibrio require a UVC exposure of 6500 mW/cm2 or more, this means an exposure time of 5.68 seconds is required to kill this pathogen

Now let me point out that even though I have published this diagram, please use this as a rough guide only, as I have found inaccuracies in it. To be more blunt; I have found the distance, wattage, and flow rate to be the MOST IMPORTANT factors in determining exposure/effectiveness. This diagram is STATIC and does NOT take into consideration the dynamics of UVC radiation penetration for which I have yet to find a good formula to demonstrate this (even in University studies).

What is often missing in any equations I have seen is the dynamics of water flow geometry, actual water flow, and wattage. The bottom line is to use this table and others you might find elsewhere with “a grain of salt” noting that these are static and even then are flawed when true output via wattage is taken into consideration.

Further Reading, References, Product Resources:

*UV Sterilization; How it works for Aquariums, Ponds, & more

*Harmful Pathogens: The Threat, mJ/cm2


Aquarium UV Sterilizer Experts for lamps, bulbs
UV Bulb; Replacement Lamps

The very best UV Replacement Lamps/Bulbs at competitive prices!

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How UV Lamps, Bulbs Work; Low/Medium Pressure, Coatings


Updated 1/2/19

UV (UVC) Lamps (Bulbs) used in Aquariums and Ponds and how they work.

Recommended further reading:
Actual UV-C Emission from a UV Bulb; Aquarium or Pond

18 Watt G11 High Output UV Lamp This post is primarily dealing with UV bulbs(or lamps), that emit UVC radiation.
These UV lamps to be referenced here are used in the Aquarium/Pond Industry. I will discuss other UV bulb types as well, since these may someday show up in the Aquarium/pond Industry.

There are two common UVC emitting lamps types currently employed for pond or aquarium UV Sterilization: the low pressure and the medium pressure mercury lamp.

G4T8 Straight Tube High Output UV Lamp *The low pressure lamp emits its radiant energy between 250-260 NM which is where UV Sterilization is most effective with a UVC efficiency of about 38- 95%.
The emission peak of the Mercury electron transition within these low pressure (hot cathode) UV lamps is fixed in both energy and wavelength.

*The medium pressure lamp emits its radiant energy between 250 and 350 with many energy spikes in between (most notably around 320 which is more in the UVB range) with a UVC efficiency around 7-15%.

CAUTION: Many Medium-Pressure UV bulb/lamp manufacturers incorrectly boast that the broad UV spectral output of these lamps is more effective, which in reality is the exact opposite!!

low and medium pressure, uv bulb, lamp comparison

Best UV Sterilizer for aquarium, pond The low pressure lamp used by most all Premium Aquarium & Pond UV Sterilizers (not always the low end UVs such as Jebo & AquaTop) is clearly the better choice based on this information.
The low pressure lamp does have one flaw which the medium pressure lamp does not suffer from and that is the low pressure lamp is affected by water (or air) temperatures and operates best between 20 C (68 F) and 40 C (104 F).
Generally this is not a major concern considering most aquarists operate their aquariums well within this range. With ponds, this is still not a major concern in that most problems, including algae occur in warmer months. This problem can be also addressed with in-line heaters to pre-warm the water.

Many UV Sterilizers come with quartz sleeves which form an air pocket between the lamps and water that in theory increases operating temperatures.
HOWEVER my own tests have shown this improvement to be nominal at best especially when compared to a well designed direct contact UV Sterilizer.
In a test with a custom 15 Watt UV Sterilizer and a 13 Watt Quartz sleeve UV Sterilizer (a well designed one at that), the increase in temperate was only 2 degrees F (I have observed up to 5 degrees depending on the units compared).
This test started at 68 F and was conducted over 15 minutes, then water was removed from the units and the temperature measured. Unfortunately the quartz sleeve is accepted as a standard that sounds great in theory, but in practicality is not a significant improvement in most applications (I would recommend them in some applications such as Lobster tanks, but even here a pre-heater would also be recommended).

Please see references for which sterilizers used in this test:
Custom 15 Watt UV Sterilizer
13 Watt Quartz sleeve UV Sterilizer

Please see this article for much more about UV Sterilization:
ULTRAVIOLET STERILIZATION (How UV sterilization works)
This article explains the benefits and myths about aquarium and pond uv sterilization

Chemical Coating in UV Lamps/Bulbs

Chemical coating on UV Lamp, Bulb A few companies now provide a coating that they claim extend lamp output and lamp life. I have serious doubts to these claims based on the fact the emission peak of the Mercury electron transition is fixed in both energy and wavelength and I don't think coatings can emit additional UV to any advantage. Coatings usually capture UV and convert the emission wavelength via further energy transitions to some visible part of the spectrum, perhaps with several spectral peaks depending upon the composition of the coating.

One such company, Emperor Aquatics, makes the claim that their UV Lamps feature an internal chemical coating that provides added resistance to solarization.
This company uses a picture of a new bulb/lamp with the coating and a one without. HOWEVER I in my 30 + years have never witnessed the degradation shown in this picture, and I suspect that Emperor Aquatics is using an Ozone producing UV bulb/lamp to make their point.
I stand by my experience that these coatings are simply a gimmick to charge more for their proprietary UV Bulbs

UV Lamps/Bulbs Starting

Another aspect of UV lamps that should be noted is how they function or start. Most quality UV lamps commonly used are Hot Cathode (low pressure) UV lamps. The Hot Cathode Germicidal UV Lamps are similar in their operation to the standard fluorescent lamps.
The Hot Cathode lamp operates from a ballast or transformer and requires a device such as the glow switch starter to preheat the electrodes in order to start the lamp. The electrodes, located at the ends of the lamp, are tungsten filaments coated with emission material and, under normal operation, govern the life of the lamp. In view of the fact that the life of the electrodes is shortened by frequent starts, the lamp life is rated according to the number of times the lamp is started.

Operation at low temperatures may result in excessive lamp blackening and rapid depreciation in ultraviolet 'C' output.

See Also this related post:
Long Life, Easy Start UV Bulbs

*Aquarium/Pond UV Sterilizer Use
*UV Lamps & UVC Lamp Types
*UV-C Bulb Specifications; Aquarium and Pond

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Aquarium UV Sterilizers; Misinformation

Updated 7/8/23 (Original Article, April of 2007)

I continue to follow the threads on forums, aquarium articles, and blogs about UV Sterilization.
It still amazes me how much misinformation is spread about this, some masked in science. As I have stated many times before, a UV Sterilizer is not essential for any aquarium, however even for goldfish I have maintained tanks with true UVs, and many other variables, I have noted a differences because of the sterilizer (especially Category A UVs such as the TMC/AAP Vecton UV Sterilizers). Many times this has lead me to a thriving tanks.
For a better aquarium forum: Everything Aquatic, Aquarium Forum, pros that care

What I also find interesting, is that many of these same persons who trash UVs, will then state a protein skimmer as essential.
I have maintained tanks with and without Skimmers (again every other possible variable the same or as close as possible), and noted the changes in measurable parameters and found that yes they are useful, however often not by much and that Mud Filters, DIY DSB filters or similar can often replace them.

Now admittedly Protein Skimmer have come a long ways since I started in this business over in the late 1970s with vastly improved, more efficient, and with less hassles Protein Skimmer such as the TMC V2 Skim Protein Skimmers and similar high end skimmers.
My point is not to trash Protein Skimmers (which have improved), but to only point out the hypocrisy of many in the marine keeping hobby that will insist on a Protein Skimmer while trashing a UV Sterilizer, despite the science behind their use.

Back to the subject at hand, here is a thread I will comment on.
In this thread one person who offered proof (albeit not of the perfect scientific nature, but as good as it can often be within this hobby) was attacked dog pile style without other backing up their statements other than criticizing his methods:

Author #1:

“If you read some scientific documents about UV sterilization of water you will know they talk usually about a standard long, 40W mercury UV tube in a 3" diameter lamp and water passing at the speed about 500 gph or less. This kind of setup delivers dosage of about 18,000 mW-sec/cm2. In order to increase this dosage you need to lower the water flow.
For example, 250 gph flow will in above mentioned lamp would be exposed to the almost double dosage of 34,000 mW-sec/cm2. This dosage is enough to kill bacteria, yeast, some mold spores, viruses and microalgae. And some aquarium grade lamps achieve this effect with unicellular algea.
To kill protozoa (like a well known from school "Paramecium" or our ich-causing "Cryptocaryon irritans") you would have to increase the dosage to the range of 200,000 mW-sec/cm2 !!!!!
This would mean that if you had 3" diameter lab-grade UV lamp with a 40W mercury tube you could give it maximum water flow of 40 gph... How about that!”

My Comment:

First, most studies I have read show under 10,000 mW per se/cm2 for bacteria. (References below)

Second, I have read articles that have shown 30,000 + mW-sec/cm2 with 90 watt bulbs at a rate of 200 + gallons per MINUTE (which even I find hard to believe). My point is it often depends on whose data you look at.

Third, there is more to treatment of Cryptocaryon than just out-right sterilization (I would not want it that high in my reef tanks!!!), there is also the Redox potential which Sterilizers improve and also general over all water quality that is aided by the addition of an Ultraviolet Sterilizer.
Finally, each unit is different and there are many variables from age of the bulb (even a 3 month old bulb has lost 25%), to temperature, design of the unit, pre-filtration, and to flow rate which I have found to be best at 20 gph (or less for most good units in aquarium applications).
See: Filter Max Pre-Filters


Author #2 (edited):
I started keeping marine fish in 1975. I first added a UV sterilizer to my tank about 1977 or '78. It was an 8 watt unit. In the early '90s, I added another. In 2005, I went back to an 8 watt unit.

Without a hospital tank, adding a new fish was always hazardous.
Back when I had no UV on the tank, once one of the fish started showing signs, the life expectancy of that fish was usually less than 3 days; they could not take the combined stress of the parasites and the copper treatment. Other fish in the tank would invariably show signs of infestation later, but would usually make it through.

Once the first sterilizer was added, the rate at which the disease spread decreased; my theory is that some of the parasites were being killed in their free-swimming stage.
After that, the first fish to show signs usually survived, and some of the other fish would never show any signs at all. Once I added the second sterilizer, I never lost a fish to Ich, though I did get the occasional infestation.
In short, there was a direct relationship to the number of watts of UV and the intensity and rate of spread of the disease.

Since I was not religious in changing the UV Bulbs (and the bulbs get less effective with time), I was also in a position to notice that an outbreak was worse when the sterilizer bulb was pretty old. Again, this didn't happen once I had two units running.
Here is a source for premium highest UVC output bulbs: Aquarium/Pond UVC Replacement Lamps

My Comment:

This person most likely had decent units with low flow rates, pre filtration, and useful discernment.
Without elaborating too much (my expanded articles have much about this), as stated earlier there are other aspects of UV Sterilizers such Redox Potential, this is not a hard test to perform; simply test the Redox without a UV and then run one for a week and test again, easy!
So many who trash persons like this have not considered all the variables if they have failed, myself I have seen UV Sterilizers not do a damn thing. These were often 8 watt units running off a sump with a flow rate of 800 gph, a calcified quartz sleeve and poor pre filtration. This is not to say a 8 watt unit (or less) cannot work, just not under those conditions.

  • The "15 Watt Custom UV Sterilizer" I made has performed well in most every application I have placed it in.
  • The standard TMC Vecton & Titan UV Sterilizer are the best when all types are considered, especially the ultra premium TMC Titan UV, which is far superior to every other brand at any price point when compared apples to apples.

What a UV Sterilizer is, is a tool for good aquarium husbandry along with water changes, filtration, protein skimmers and more. In many of my side by side applications with and without, the UV was just one more piece of the puzzle to improved water quality in let’s face it, an artificial environment (unless we want to kid ourselves).

I can think of one experiment in particular with several goldfish tanks at a large service customer of mine. All these tanks in particular had canister filters, cleaning and the same feeding schedule and bio load; the only difference was UV Sterilizers.
The difference in amount of diseased goldfish, growth and color was very noticeable (the vice president did not kno we were performing this experiment and even commented about why some tanks did better than others, after which she had us install UV Sterilizers on all).

Copyright; Carl Strohmeyer

Please read this article about UV Sterilization for a MUCH more in depth understanding of How a UV Sterilizer Truly works:


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