I have been told that chromis are one of the larger aquarium schooling fish. My well trusted LFS told me that they need larger tanks arond 90 if you want a couple. My LFS also told me that I should go with gobies instead.
In addition I have 3 clowns. The chromis I have are the little blue/green. They are so unlike the blue yellow tails I have in my 29gal. I have never seen them do any picking at each other or anything else. Although I have seen them feed on what I think was a spawning of some sort. Kind of a slimy thread event. The 75 has been running since Oct 1, 02 and also has a handfull of little left handed crabs a scarlet reef crab, 3 fighting conchs, 1 olive snail, 1 brown brittle star, 1 emerald crab, usual pods etc. A few mushrooms and zoothids. No sump. Contemplating a large sump in the basement, closed loop, lighting upgrade to MH. Running two Penquin 660's for circulation and the PM HOT1 skimmer. Actually just waiting to get the hood built for the lighting. Currently 2 NO bulbs. Nothing requiring high lighting at the moment.
Plans include some corals down the road. An anemone. No Tangs or Angels or other larger fish.
I saw 15 green chromis in a 175 once, they all are thriving 6 months later.
It alsohad a hippo tang, several wrasse's, flagfin angel, and a coral beauty.
It wasn't my favorite set-up, I thought there was too many.