I have 2 hagen canisters supplying one ladder in my tank, to minimize the fluctuation of co2 during replenishing. Each canister has a valve controlling its output. The sequence of replenisment is such that when one get refilled the other is at the max reaction rate. I would shut off the valve of the one being refilled so as not to disturb the flow.
I am thinking of adding one more canister to boost the output.