had a 8, 14, 20, 28, 55, 75, 135 gallon. now im looking at a 185 or 210. they all have their pros and cons. all i can say is go as big as u can afford.
smaller does require a lil more time to make sure u dont have a lot of paramater swings. big will cost more in equipment and electricty. both are expensive. just go big