Since none of the two reactors I use work flawlessly I am thinking of two other ways of getting the gas into the water: 1) by using an air diffusor, 2) by letting the gas bubbles enter the intake for the external filter. I will probably try this soon and then get back here with the results.
The diffusor will probably waste a lot of gas, but the gas is cheap. Letting the gas into the external filter will probably mean that all of it is used, but what happens to the "false gases"? And does none of the gas trickle its way up through the filter medium and then just flow out? Will the filter be filled with the non-CO2 gases?