I was doing some research on bacteria and came across several articles dealing with UV lights and their ability to kill Algae, bacteria, and parasites.
The consensus of the articles and from reviewing various manufacturers products is:
To kill algae you need around 25 watts per 1000 gph of flow. (40 gallons per watt)
To kill bad bacteria you need 40 watts per 1000 gph of flow (25 gallons per watt)
To kill parasites and be most effective you need 100 watts per 1000 gph (10 gallons per watt)
So in my pond with a 3500 GPH pump I need 88/140/350 Watts of UV Sterilization depending on the job to be done.
One article also wants high turnover of pond volume at the higher wattage to be effective. Ie up to 4x volume of pond.
But if you have a filter on the outflow side of the UV you may have too much flow for biological filtration to occur.
Most of the articles agree that the good bacteria are not impacted. None mentioned how to get bad bacteria to flow through the water column other than to make sure the pond has no dead spots. Circulation is going to be only real option to move bad bacteria through the pump. A good prefilter was advised so that small particles do not reduce the effectiveness of the UV.
Overtime the bulb will diminish, junk will block the crystal tube, and the ballast will wear out. These all need quarterly maintenance and inspection. Placement can be either vertical or horizontal.
Here are my thoughts. I will purchase 80-100 watts of UV initially and add more as budget allows. Many are modular systems for ponds. I also do not see the need to run 350watts all the time, so perhaps some could be on timers and cycle on/off. OR I may merely put it inline for my skimmer circuit which would shoot the dead algae/bacteria into a small pressurized filter then return the water to the pond via the jets. My planned skimmer circuit will only be about 900 GPH so I could get away with 1 80+ watt unit (usually two 40-55 watt units’s running parallel), but the volume of turnover would be less than ideal for my pond. I would eventually move the uv from the skimmer circuit to the main bottom-drain-to-filter circuit as I increase the wattage.
I like the models with the 1.5-2″ union fittings and will be looking for a quality built light. I will not likely purchase one of the higher end models in stainless steel. Cost on these items varies greatly depending on the housing and size of bulbs.
