Ok.
Just to straighten out design details on how the Ca works:

Co2 and water can enter the chamber through the bottom through the media to the top of the chamber to the recirculation outlet.

A seperate output is then accomodated for the effluent water to the tank.
located somewhere in the return line to the pump. This being a small outlet only which can be controlled.

I am assuming that this water outlet can be the same source you use to get samples to measure the Ph of the Reactor.

Can there also be some type of accomodation made at the top of the device to accomodate any excess C02 to be bled off?

Also some type of controller should be provided to keep the Co2 in check.

Does it seem like I have it straight now?