Just to throw my newbie .02 in, I have a 24 gallon aquapod. I thought that since clowns were just sooooo sweet and all that, I could have 5 of them in the tank. I got two black and white 2 false percula and one true percula. I was warned by some on this forum that I would have troubles. I had just bought a used 120 and began cycling it. I had a little mistake with acid buffer that left my 5 clowns hanging vertically and panting for air. One hopped out of the tank completely. I threw them all into the 120 thinking that things really couldn't get any worse for them.
Soon after, I noticed that the black and whites were ganging up on the lone percula, chasing him, harrassing him, nipping at him, etc. Luckily, I had gotten the aquapod under control and put him back in there to be with his BTA. The other two pair are happily swimming around in the 120, having a virtual palace to themselves.
Today I added some hermits, a yellow watchman, and a hawkfish. Tomorrow I will try to get some starfish and snails.
I have to say that I didn't believe MY sweet little fishies would be so nasty to the lone percula. I'll look into getting him a mate ASAP.