My green water isn’t clearing. Why?

Check that bulb is connected properly, and that the unit is wired in correctly, and on. UV should be on for 24 hours per day. Consult the recommended flow rates on the packaging. If water flow through the unit is too great, the contact time with the UV rays may not be long enough. Slow down flow with a controllable pond pump, or a ball valve. Check the pond volume calculation to enure that you have the right size of unit. If unsure, always go bigger. Check the age of the bulb. A UV bulb needs to be at its most effective from March until September in the UK. Install a new bulb every March. Always combine UVC with effective mechanical filtration, to remove debris which would otherwise shade the bulb, and to capture dead and damaged green algae cells after they’ve been exposed to the UV.