My reactor internally circulates at about that rate, but the actual flow in/out of the unit is very slow - just a rapid drip, really. Maybe this is what you mean, but if you are actually running 300 gph out of the units then you are not running it properly, and both burning through CO2 much faster than you need and releasing it to your tank. With my dual chamber MTC ProCal I measure effluent pH to about 6.5 or so which requires about one bubble every two seconds or so; maybe slightly faster.