Red Worms in Your Biofilter: Harmless Bloodworms

What They Are

The small red worms in your lava-rock biofilter are bloodworms—larvae of non-biting midges (Chironomidae). Females lay egg masses in the water; larvae build tiny tubes in the filter media and feed on suspended organic matter.

Are They Harmful?

Absolutely not. They are a sign of a healthy, organic-rich filter. Fish love to eat them. When they pupate, you may see a cloud of tiny gnats when opening the filter—just a nuisance, not a threat.

Management

No action needed. If numbers seem excessive, clean a portion of the filter media at a time to preserve beneficial bacteria. Enjoy the free fish food!