A 30 tank should have no more than 4 or 5 small/mid-sized fish. A flame angelfish needs at least a 70 gallon tank. A mandarin needs a constant supply of copepods. You either need a several hundred gallon tank or you need to introduce copepods daily to keep a mandarin. The mandarin will slowly die of starvation if you get it with or without a refugium. If you start with a school or shoal of chromis, they will most likely kill each other off until only one or two are left.