Bluegill tank is dark

[Michael Mansur]

After a winter of spending a fortune trying to keep my tilapia alive, I have decided to stick with bluegill. I also wintered them over and never had to even heat the tank. But I am having a hard time keeping the inside of the ibc tank clean. I have cleaned the film off but it comes back in about 10 days. The water in the system is clean and clear but the tank is so dark I can't see my fish. Is possible to put carp or catfish in the tank to help with this?

[Scott Roberts]

I'd suggest using a flashlight.  The biofilm buildup on the sides of the tank is a good thing!