We are limited to a 55 gallon tank due to living in an apartment, space etc. etc. etc. I know that you are only supposed to have 1 fish per gallon of water. Does that include like fresh water crabs and such? Because my daughter likes the cichlids and tetras, and me and the fiance like the crabs and sucker fish. Would these fish do well with each other and is my thinking on the tank right?