Found this on another forum:
Mixing clowns
Hi Bob,
<Lego>
My Question is a classic that I've seen mixed answers to. Here goes: Is it possible to have two distinct mated clown pairs of different species in a 55g Long tank? Specifically a mated pair of tank raised Ocellaris clowns and a mated pair of tank raised black Saddleback clowns? The tank will have lots of live rock which can be arranged to break up territory. I would be adding the two pairs into the tank at the same time.
<Not a good idea... if the tank were twice this size...>
These are two of my favorite species of fish. I have visited a store that has both species in one tank, and they appear to get along - the workers at the store said that Maroon clowns are the ones that don't mix well. Yet I always here the simple phrase "don't mix clowns" .
<Can be mixed when small... best not to as "mated pairs"... I suggest trying other species/families>
I'm not planning on keeping any anemones, so that shouldn't be a factor.
<With or w/o anemones... Bob Fenner>
Thanks, J.T. Gilkeson
Plenums and ultra deep sand beds > all other setups!