And it depends on how each fish will use the space. Think about a reef - you have at least 3 different zones. There's the bottom, where gobies and mandarins live. There's the open water where the chrmois, tangs, antheas etc live. And there's the rock work, where the hog fish lives, along with the 6-line wrasse and the miniature angels among many others.
Let's say you had a 250g tank. PERFECT size for a tang!! But how many are you going to put in there? At some point, it's all tangs and none of them have any room to swim anymore. You'd be better off with 2 or 3 tangs and then utilize the rest of your reef. Get a bottom feeder or two. Get a few fish to keep the rocks clean.
Now employ that same strategy when stocking a much smaller reef like your own 30g tank. You have 2 clowns. If you can find a nice size colony of big palys - I'll bet the clowns would stay in there and host their lives away. That kinda keeps them contained in one spot. The damsel is going to get a couple inches long at best. But it will stay in the open water and occasionally swim in and out of the rocks. It will need a home though. Each fish is going to want a spot to sleep in. It needs to be calm water or somewhat sheltered - they don't fight the roaring current day and night in the ocean.
IMO your stocked up to the max. You might be able to squeeze a small goby in there if your doing good maintenance. Be aware of the bio load and be honest about your filtration. Try and have the fishes best interest at heart - not necessarily your own. Hard to do.
I have a 30H tank with a single 2" clown fish. I want a rock dweller and a bottom feeder, but I've been killing for for some reason and tired of the hassle so I just have my 1 clown and the rest of it is covered in coral. The clown actually died a few months ago too. Just quit eating all of a sudden and was dead in a week. My wife made me run to the LFS and buy a new one while the kids were at school.
My 29g frag tank - one damsel. I actually built the frag tank because I rescued the damsel from a trip down the American Standard whirlpool of death. His owner was giving him away. His craigslist add said he was gonna flush it on a Friday after work. I picked it up free on Thursday after work. But the damsel was MUCH larger than I expected and he went stir crazy in my 10g frag tank. So I ended up doing a big upgrade on the frag tank just so that stupid damsel had more room to swim. I won't put anymore fish in there.
Lots of people would put the damsel and the clown in the same tank.
I should just stop rambling. :shock: I don't like fish anyway. I keep one in each tank to make some waste.
Ask somebody else. :mrgreen:
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