I would recommend the Aquatop CF500UV 5-Stage Canister Filter with 9W UV. It's rated at 525gph. I descided to get two of these instead of a FX5 since it was double the filtration with the UV as an added bonus. Company has been great and they have great products. My water has never been clearer.
http://www.amazon.com/Aquatop-CF500...e=UTF8&qid=1342993819&sr=8-1&keywords=aquatop
Actually the fx5 without media (running empty) is around 600gph. With media?????Actually no its not double as these filters have about 525 gallons per hour and the fluval has around 900
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