There is a film that always builds up lightly on the top of my fishes tanks like a clear coat. What is this?

How can I avoid this from happening?There is a film that always builds up lightly on the top of my fishes tanks like a clear coat. What is this?
Are you using stress coat or other fish oil based products?





Increase surface agitation and it will mix in with the water and attach itself to your fish.





Still increase surface movement if its not a medication as the filter will catch it.

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