The Un-Filters 401 Chapter 3
Halve the Flow, Double the Dose
UVC Exposure is directly related to the rate of water flow. The faster the water passes through the housing, the less time individual cells will be exposed to the UV light and higher the wattage will have to be to hit the algae with that minimum 15µWs/cm² exposure. The single most common mistake made with UV’s is to flow too much water through the units. The slower the flow, the greater the exposure, so consider teeing off part of the total flow from the pump and running it separately through the UV. If you don’t get good algae control within a few days you can easily double the exposure rate by HALVING the flow rate through the UV. Each manufacturer has their own guidelines, but as a general rule of thumb, you’ll want to set up the UV so that all the water in the pond is circulated through the UV at least once during the time it takes the algae to reproduce, to keep ahead of the reproductive rate. That rate will vary during the year, highest when the water is warmest and the days longest, but it generally ranges from 3-8 hours. If you pass all the water in the pond through every 4 hours you should be ok, so in a 4800 gallon pond a rate of 1200 gallons per hour should be sufficient.
UVC Exposure is directly related to the rate of water flow. The faster the water passes through the housing, the less time individual cells will be exposed to the UV light and higher the wattage will have to be to hit the algae with that minimum 15µWs/cm² exposure. The single most common mistake made with UV’s is to flow too much water through the units. The slower the flow, the greater the exposure, so consider teeing off part of the total flow from the pump and running it separately through the UV. If you don’t get good algae control within a few days you can easily double the exposure rate by HALVING the flow rate through the UV. Each manufacturer has their own guidelines, but as a general rule of thumb, you’ll want to set up the UV so that all the water in the pond is circulated through the UV at least once during the time it takes the algae to reproduce, to keep ahead of the reproductive rate. That rate will vary during the year, highest when the water is warmest and the days longest, but it generally ranges from 3-8 hours. If you pass all the water in the pond through every 4 hours you should be ok, so in a 4800 gallon pond a rate of 1200 gallons per hour should be sufficient.
