You have a UV clarifier, yet you’re still experiencing green water
It may be time to change your UV bulb—two seasons or eleven months should be the max. If the UV bulb is fine, then see our section on Green Algae.
Remove the quartz sleeve or glass tube carefully from the housing. Using distilled white vinegar, hot water, and a soft cloth, thoroughly clean the sleeve removing all minerals, smudges, algae, etc. Dry carefully and re-insert into the housing. Be sure to not leave finger smudges for best clarity results.
Make sure your pump and filter are properly sized for your pond. Good water circulation is critical. Using the 50 percent circulation rule: The pump should circulate the entire volume of the pond at least every two hours. So, if you have a 1,000-gallon pond, you need a pump that will discharge back to the pond at least 500 gallons per hour.