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Persistent Foam in 700-Gal Koi Pond: Overstocking = DOC

700-gal pond, cascade 24/7, UV filter not 24/7. Several koi, ~30 goldfish. Foam at cascade base & UV return. Lab tests: no phosphates. Water clear but foam mars appearance.

Cause: Dissolved Organic Carbon (DOC)

High fish load → waste → DOC → foam at agitation points. Lab didn't test DOC.

Solutions

Water changes reduce DOC.
Activated carbon in filter adsorbs organics.
Reduce fish load — 700 gal for "several koi" + 30 goldfish = severe overstocking.
Time for bigger pond.

Foam won't stop until bioload drops or carbon/water changes maintained.

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