the picture that tom posted with his article is confusing to many. that photo showed the 2 options for the venturi feedback loop, either from the top or from the side. there are only two holes you need to drill, one for the co2 input and the other to connect the venturi. his recommendation to have the venturi 3" down from the top is about right. i drilled mine about 2" down and it started to draw excess co2 after being on for a couple of hours. didn't notice any difference in terms of plant growth plus didn't like the pzzzft of the impeller breaking up that vented gas so i disconnected it.
i really don't know how you'd connect the venturi on a canister. he used a powerhead that recirculated the vented gas before (not after) the impeller to create mist. you could feed it into your canister intake, but injecting co2 into a canister has issues.
Last edited by moke; 12-17-2020 at 06:50 PM.
Reason: add 2nd paragraph