you know how stocking levels also depend on how "messy" the fish are...ex) in a twenty gallon tank you could probably get away with about damned near 35 neons about 1 inch each...where as you can't put 35 1 inch guppies in a 20G tank....
How messy are catfish? I have 2, 20 gallon tanks one with:
1 snakeskin gourami (3inches)
2 bleeding hearts (one inch)
and 2 catfish (one inch each)
the other has 2 hopefully breeding gouramis 2" each which will go back into the other tank soon
how many more 2 inch cats do you figure I could add without overdoing it water wise?