I have a 55 gallon and right now have 1 clown, 1 sixline, 1 yellow watchman, 1 yellow tailed damsel and 3 chromis, totally right now about 12-13 in. I know there is no specific rule for the amount of fish you can keep, that's a different topic. What I want to do is add one last fish, either a flame or coral beauty angel. I feel that because my fish are small, I can get away with another. But about how long does it take for a fish to reach adult size?