This occurs where water is disturbed or agitated by a venturi or waterfall and the resultant bubbles will drift around the surface until they burst. These bubbles retain their shape because of the stabilising properties of complex dissolved compounds within the water. Largely organic compounds build up in the water to levels which encourage stable bubbles to form. Dissolved organic compounds are a by-product of the metabolism of Koi and other aquatic organisms, and are deposited into solution.

Protein levels within the water can also rise through the inappropriate use of higher protein diets, which can leach other soluble compounds into the water, also leading to the formation of foam on the waters surface

The best way of keeping foam down is by using protein skimmers. If bubbles want to form, then why not encourage them to do so under controlled conditions in a pond protein skimmer?

Borrowed from marine fish keeping, several pond models are available and through the vigorous aeration or movement of the pond water, encourage the formation of a protein-rich foam which is collected and then removed.
Plenty of good water changes, keep the pond base well vacuumed and the installation of a water polisher and filter including “vortex clean” and good a UV algae lamp will also add to foam removal.

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