Never tried S/W myself (yet) - but as I understand it - the larger the tank, the simpler it is to keep it stable. A 500 gal S/w tank would almost take care of itself, but a 5 gal would need watching carefully. If you know what you're doing then fine, but when someone says go with a 55, they're just trying to make it easier for you. It's all about the water chemistry.