water quality question

[sehkmaa]

I have an oily kind of sheen on the surface of three of my tanks. 2 10's and 1 90 gallon. In each ten are 3 Bettas, partitioned. In the 90 are two Cichlids, 2 Giant Danios and 4 Black Tetras.
The Bettas are being medicated right now to prevent anything after an unsuccessful spawn and I can do water changes for a couple of days.
Please help
Sehkmaa

[amanichen]

This is most likely proteins from processed food. Ensure that the tank has plenty of water circulation, don't overfeed, and keep up on your water changes.