Check ot the Aqua-Medic Reactor 1000. It will plumb inline with your 404 and will accept a standard air line for your CO2 supply. Best thing is...it's entirely external. No reason you couldn't build one if you were so inclined!
I've got one and it works great with my pressurized CO2. No bubbles in the tank and it's very efficient.
The way I understand thoe membrane reactors, they must be placed deep and in high current to be effective. I looked at them, but was concerned about algae growth and junk blocking the membranes.
If I read my chart correctly, to maintain high pH and high CO2, you would have to have to have EXTREMELY hard water. My calculator says you would have to have 200 degree of KH to achieve 19 ppm of CO2, but I don't know if that calculator can be trusted at such extremes. You'll just have to try it.