First off, I swear I'm not stalking you, I just post in a few places.
I didn't notice the biowheel over on thebarreport.com. Usually you want high diffusion and dwell time, with small bubble to offer just enough mass to rapidly break the dead water barrier around the leaves. Pumping the CO2 through an intake that operates on pouring the water over a wheel then splashing/laying it out over the surface of the water is a little detrimental to the process.
Want a cheap fix? Get a small submersible pump like the Rio series (I use a Rio 180 in a 20g). This should cost maybe $12-$40 depending on the size you choose. It'll run along side your HOB.
Pull out the impeller, cut each fin in half horizontally then bend the top fins in one direction and the bottom in another. I prefer a hobby knife for this; even good tissue or fly tying micro tip scisors won't do the job.
From there, drill a hole in the intake cover the same size as the CO2 line. Push the CO2 line in, face the cover downwards. There should be no need for adhesive to keep the line in place. From there, work at getting the distribution right; look for low horizontal or downwards angled flow. It might take a little tweaking.
This works for DIY or compressed, and I prefer it over diffusers by far. This system is easier to maintain, way better efficiency and distribution of CO2.
Good luck with the system.
-Philosophos