So I ended up buying a 20 gallon tank the other day and haven't really had time to set it up with finals coming up. when we were initally looking for a tank for me, my dad sort of fell in love with that Eclipse 12 system (the one everyone recommended not to get). He decided it was "the perfect size for (his) office and (came) with everything (he) needed" :? He's already bought it and is cycling it as i speak. He pretty hellbent on using black neon tetras. He asked how many tetras he should have at max. He also asked what the biggest/friendliest showcase fish he could use(and how many). In regards to my tank, I was wondering if cory cats are really a neccesity in a tank.