On tanks over 200g I say at least two canisters turning over 1000gph combined flo. That will give you an industry standard 5x approx. turnover. Remember, the FX5 advertises its flow at around 900gph, but that is an empty canister. Once full, the FX5 slows way down meriting the addition of another FX5. For the money, (I'm in about $350) I have an overflow, sump and return turning 1800gph through my 210. The nice thing I like about a sump is its ease of expandability. I have never regretted the change over from canister to sump. If I want more flow, add a return pump or increase the size of the single, provided of course that the overflow will handle the extra flo. If not, add another overflow. A sump lets you expand, it gives you options.
