This may be old news but for anyone having a Hydor Koralia #4 powerhead I recommend this product, it is a Sure Flow 1600. It's a Maxi-Jet upgrade kit for about $25. It comes with 2 proplellers, I tried the white propeller and the PH just started backwards. I than tried the black propeller and it works great. I seen somewhere that it boosts the Hydor#4 from 1250gph to 3000gph and I have to back it up 100%. I have two of the #4's in my 144G tank and have only did this to one of them, I'm too afraid to do it to the other one as I think it will be way too much flow. Pretty cheap upgrade for the money.
