From everyone i've spoken to on this subject say that once you go over a 100g tank, you should use a sump. They say that Canister's do not have enough oxygen to support enough beneficial bacteria for anything over a 100 g tank. So I'd say for that size tank, go with a sump. You can build one out of a plastic storage box from walmart fairly easy and inexpensive. However, a 600 gallon might take more than one of these sumps!