Okay, so I decided to make a reactor given that the ones you buy are either cheaply made or made for higher flow than my canister. I know the normal design is with 2" pipe, but since my canister filter (Fluval 204) only puts out 150gph max, I thought it would be better to use narrower tubing. I used 1 1/4", since I already had that and thought it would work. I have it connected and to my surprise it doesn't the flow much at all. I used the biggest fittings that I could find that would work.
So here's my observation, and looking for advice on what size to use on my next attempt. Bubbles are coming out of my outlet and floating to the top immediately, so I did get rid of the "fizz" created by the diffuser, but at the expense of actually absorbing the CO2. It seems to actually be absorbing LESS than with the diffuser. I kept the bubble count the same and kept an eye on it.
So what should I try next, go with the standard 15" of 2" pipe like the design calls for? I was afraid of buildup at the top, given that my output is only 150gph, but it looks like the 1 1/4" has kept the flow too high. Another option would be to add a valve to increase the backpressure?
I should also note that my tank is 29 gallons, fairly heavily planted.
I could also try using this connector at the bottom to add backpressure to the reactor. See pics, much smaller opening.