So on this last Sunday night, I just hooked up a cerges reactor to my Fluval 404. I went with 5/8" ID / 7/8" OD braided vinyl tubing from Home Depot. I had to push with some decent force to get the tubing on the barb connectors, but it is working just great. For me, on the 404, that tubing was a perfect fit. It is thick enough that you won't need the plastic nut where it connects to the valve bracket. You could still use an "O" clamp if you want some extra safety.