Green Pond UV Clarifier
Green Pond UV Clarifier or Sterilizer Use
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.
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.
See Pond Veggie/Bog Plant Filters
Other methods of Green Pond Water Control are listed here: POND ALGAE CONTROL Often many basic methods still fail to control these algae blooms and this is where a UV Sterilizer (Clarifier) comes in.
The key is flow, correct wattage as per flow, dwell time, and pond turnover
With flow rate, this should be under 50 gallons per hour per watt of UVC for most Compact UVs (40 gph per watt for many low end UV clarifiers). With higher dwell time UV Clarfiers (generally straight tube designs have a higher dwell time), this rate can be as high as 60 gallons per watt of UVC energy.
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 that makes in the sun and nutrients and breeds these green water producing algae spores.
You can test this with dyes or even relatively harmless aquatic products such as Methylene Blue
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 25 Watt TMC Advantage UV Pond Clarifier (which is one of the best if not the best) for a pond that is 5000 gallons run with a flow rate of 1200 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.
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 1979, 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).
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
See: Dwell Time Test)
Then there are all the submersible UVs such as the AquaTop that while I have used them, with some success; these ultra low cost UVs simply do not hold up long term in a harsh pond environment and eventually fail. As well these UVs often can clear green water unless conditions are otherwise optimum.
Resources, Recommended Reading:
*Pond Care Information
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:
UV Sterilization Use Beginner to Advanced