Ca reactor question

[gudgreef]

In Baencsh's Marine Atlas on page 101 there is a 'ca reactor' that consists of introducing CO2 prior to a canister filter that has crushed dolomite in it.  Am I missing something. Doesn't the CO2 + H20 have to recirculate and be metred out. Would this require a 'pH controller'? Would love any input if anyone has seen this plan.

Thanks

Tom