I mentioned previously in a thread that my bass hit the top of the tank and she nicked her face. It got a little white (nicks). I thought it could be HLLE.
Top fin was also damaged with white stringy stuff.
It wasn't. Salt and StressGuard solved it. But she was eating well and otherwise ok.
In your case if you want to save the bass you need to get rid of that catfish. Otherwise the bass will die. Most anything you put in with that RTC in that dinky tank is going to get roughed up.
I don't see a divider as being a solution. Not for that tank. Like I say, make a decision and divide the fish into different tanks or watch the pbass suffer and die. You need to move quick.
Bass will get dark when they aren't feeling great or when they are "sleeping".