Here is where I run the hose from my CO₂ bottles into my Eheim canister filter. The canister filter holds the CO₂ in the water for a lot longer than any other way I know of. This greatly helps getting the CO₂ to diffuse into the water. I used one of the nipples that come with the really thin air hose to splice it with the thicker hoses. I drilled a small hole in the center ot the green plastic sheild and stuck the nipple into the filter pickup. The canister filter pump breaks up the bubbles into tiny little bubbles that stay in the tank for a while even after they are pumped back into it.