Co2: Can I do this?

What's your current setup? Canister filter? Sump? Do you have power heads in the tank currently? The more info you can give about what you have to work with the better suggestions we can give you.

My first thought is that you'll waste CO2 with the bubbles not completly desolving, and its fairly expensive. I have an inline reactor based off of Tom's venturi reactor design posted in the CO2 section (less than $20 in materails to make). This way I still have a great reactor without adding anything extra to my tank.

 

I am having trouble figuring out how this works. Does one just use this pump to circulate water, but takes the gas-out tube from the CO2 canister and connect it to the venturi intake of this pump? And because it's a closed loop, and I assume fairly airtight, the CO2 gets dissolved "better" and circulated into the tank more efficiently?

How does a "needle wheel" differ from other impellers? (I can see the visual difference, but how does it affect water flow in reality?)

Also, is this an external pump?