allan a canister filter will really only work as a phosban reactor if the pump running the canister is around 200gph or less so make sure you dont have one thats pumping to quick. Phosban needs the water passing through at a slow pace, which is why its best to buy a actuall reactor with a very small pump. You do not want the water jetting by at a high rate of speed, you want it in contact with the phosban for as long as possible.