I fell in to the same trap when I first did diy co2, about how certain things were called. Do a google search for diy co2 reactor and most likely you come up with how to do a diy co2 generator. I guess when you google things google it by what you want it to do. If you want to make co2 search diy co2 generator. If you want to diffuse the co2 I search diy diffuser which then results in a diy reactor!! There are several different diffusers out there. I believe it is passive, which is just putting an airstone on the end of the line and letting the current move the co2 around. Then I believe there is also mechanical, which is more like a reactor where you are purposly breaking down the co2 and trying to get 100% dissolution.
As cobfreak mentioned above, I did build the dual venturi reactor and personally it does a great job, but I dont like it. Tank is filled with co2 bubbles. IT need tweaking. I am working on it. The bubbles are too large. I believe I read on tom barr's website you want more of like a vapor. Where the bubble is so small it cant fight current. I havent been able to work on mine yet, work and soon overtime and school will make it harder, but ill keep plugging away at it.
cob whats your ph at today?