thats gonna depend on what you plan on keeping as far as corals go....and if you want your sand, if your running it, to stay put........ a good general rule is....softies and LPS, between 20- 40 times the tank volume and if you get into SPS higher then that.....I have about 10000 gph of turnover in my 110g....just an FYI, the magnum koralias are the size of a football
....if its within your budget, look at a vortech MP40 of one of the bigger tunzes
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260g mixed reef, 105g sump, water blaster 7000 return, Bubble King SM 300 skimmer, Aqua Controller Jr, 4 radions, 3 Tunze 6055s,1 tunze 6065, 2 Vortech MP40s, Vortech MP20, Tunze ATO, GHL SA2 doser, 2 TLF reactors (1 carbon, 1 rowa).
http://www.canreef.com/vbulletin/showthread.php?t=50034 . Tank Video here
http://www.vimeo.com/2304609 and here
http://www.vimeo.com/16591694