A koi pond UV clarifier is most useful when the water is green from suspended algae. It treats water passing through its enclosed chamber. It does not remove leaves, process ammonia, or scrape string algae from the pond walls.
Clarification vs. Sterilization
Manufacturers may publish different flow ratings for algae clarification and for a specified disinfection dose. These ratings are not interchangeable. A hobby unit that clears green water is not a guarantee against parasites, bacteria, or viral disease.
UV effectiveness depends on dose, flow, chamber design, lamp condition, and water transmission. A larger wattage or wider chamber alone does not tell you how the installed unit will perform.
Choose the Unit Around Actual Flow
- Calculate the pond volume and the flow that will actually pass through the UV.
- Check the exact model's clarification rating and installation requirements.
- Account for pressure loss, bypasses, and restrictions in the circuit.
- Leave room to remove the lamp and sleeve for servicing.
For example, a pump supplying two branches may deliver only part of its total flow through the UV. Use that branch flow when evaluating exposure, while also checking whether enough pond water is being treated overall. The number printed on the pump box is not a flow measurement.
Keep the Sleeve Clean and the Lamp Current
Deposits on the quartz sleeve reduce light transmission. A lamp may still glow after its effective output has declined. Clean and replace components on the manufacturer's schedule and check seals after servicing. Disconnect power before maintenance; never operate an exposed UV-C lamp or look at it directly.
If the Water Stays Green
- Confirm the problem is suspended algae, not brown sediment or attached algae.
- Check power, lamp age, sleeve condition, and the correct replacement parts.
- Verify plumbing, bypass position, and flow against the model's rating.
- Remove accumulated waste and maintain the mechanical filter.
- Continue testing ammonia, nitrite, and oxygen conditions even as clarity improves.
Reference: Aqua Ultraviolet's installation and flow FAQs. Read the separate green-water troubleshooting checklist and the filtration overview.