Tiny Worms in String Algae: Harmless Larvae or Worms

A 300-gallon pond with UV filter and 24 goldfish has string algae containing tiny worms. Owner asks if they’re beneficial and if a 9W UV is adequate.

Worm Identity

“Tiny worms” in algae are typically insect larvae (midge, mosquito) or oligochaete worms. They’re detritivores—part of the cleanup crew. Harmless unless they clog the filter.

UV Sizing

9W UV on a 1,300 GPH pump for 300 gallons is borderline. For green water control, aim for 2–3W per 1,000 gallons with proper flow (not too fast). A 9W unit at 1,300 GPH may have insufficient contact time. Consider a dedicated UV with flow control or a larger unit.

String Algae Note

UV doesn’t control attached string algae. Manual removal, nutrient reduction, and barley straw extract are better approaches.