Dude you got a 640g do it right make youself a good sump If you don't have the cash or cant find a used tank look up rubbermaid stock tanks. Sumps are very simple to build and there are some great threads on this site. For the money you would spend on to big canister filters, you can build a sump for less and the canisters you will end up ditching in the long run. Is the 640 drilled or does it have a built in overflow box?