I have a Reefer 250 but had a trigger custom sump made which is about 14 gallons. So I have a great amount of space in my first chamber and can fit either unit there. The price difference isn’t that much and the 500 is actually shorter so I’d have better clearance on the top. Width isn’t an issue for me. At the moment I just have 3 fish and about 10 corals. I don’t want overkill per se but thoughts ?
