Ian, K4s sound like a lot of gph.. 1200 x 2 = 2400pgh
The tank I have is a 3ft 50 gal tank, with the sand and live rock, I think volume is more like 40-45gal. So,
30 turns x 45 = 1350gph < 2400gph
I am not counting the flow from the canister/sump. The price difference between K3 vs K4 is...