I have a long 6 gallon and my filter is on one end, as shown in the photo. I have the filter running with a low flow, cuz I have a betta and they don’t like heavy currents. Even when I turn the filter flow up, it doesn’t help much.

I have an air stone on one end to help break the surface tension of the water, but the biofilm gets so bad. It’s clogging up my filter and will cover 60% of the water surface. I have to clean it off everyday. It’s a pain having a long tank, cuz the filter flow won’t reach the other parts of the tank.

Can I do anything else to prevent it? It’s pissing me off.