+1. Even the smallest tang is too big for a 30G tank. And as stated, those clowns will eventually duke it out and I agree that the end result will be 2 clowns. Now, in a 30G tank, you can have anywhere between 10 to 15 inches of fish, depending on the filtration you have. It depends on whether you have enough mechanical filtration to remove all the waste they produce. Also, study what you want to put in your tank. Some fish require a swim lane that your 30G will not provide. Some fish are aggressive towards others, so you should consult with a compatability chart. In many cases, you even have to look at gender of fish if your going to have over 2 of any one kind.No, too small for any tang. And the 4 clowns will not work long term.