um yeah... you might want to separate the oto, because those things will eat the slime of whatever fish they are housed with, and eventually, both will die.

No, you can't treat bloat, but you can quarantine the sick fish. Then take all the other fish out of the tank and empty it. Bleach the tank and ornaments, throw out the filter media, and pour boiling water over the gravel sveral times to disinfect the tank. Since bleach it basically the same stuff ...

Did the fish die?

Buy a filter 4 the 5 gallon tank...

don't Corydoras Agasizzi have spotts?