How many fish can you hold in this bad boy? I have 3 GloFish right now.. I'm intewrested into catfish too
What kind of catfish? There are so many types and some grow to be really big. Also you have to consider the water requirements for both. Goldfish have very different water requirements than most of the catfish available I believe.
15 gallon column footprint is just 13x13 inches. It's not really ideal for most fish sadly.