This is a pond at a school habitat garden. I have drained, cleaned and refilled it, but this film keeps returning. I’m thinking it could be caused by the rust. We have gambusia in the pond and they are staying alive despite it all. The film is slick, rainbowed, and clumps together. Suggestions on what it is? Also, how should we treat the rust? The tank is only a few years old and should not have rusted this badly so soon. Also of note - because we are on an elementary school campus, we can only have 6” of depth, so the majority of the tank is filled with rocks and soil. Thanks!
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