Hi, I have a 75 gal. tank with 20 gal sump. Fish and reef. Up and running very well for about 3 yrs. Fish have out grown my tank. The buisness I bought it from set it up so I didn't question him. Yes, dumb move. Anyway, they are healthy and happy. (largest- blue tang, and dwarf lion) Want to give them more room but wondered which is harder on them. A new tank (tricky) or leave well enough alone. I do weekly changes and all my parameters are good. Thanks whoever gets some time to answer.