I run DIY CO2 in my 10 gal BioCUBE so have no flow controm other than setting the generator under the window where it is cooler to slow the reaction after a fresh charge and moving it away from the window when CO2 production falls off a week to 1 1/2 weeks later
My drop checker is yellow (too much CO2) right after a charge, turns green (right amount of CO2) for a while and then to blue (too little CO2) toward the end of the second week or in the third week when CO2 bubbles deminish
I can't see any change in fish behavior no matter what color the drop checker reads
I don't notice the color changing from yellow first thing in the morning to green after the lights have been on for a while
Whenever I calculate CO2 concentration based on hardness and pH (chart and formula somewhere on the Web) it is always in or below the recommended range
My plants directly under the lights are more likely to pearl just after the generator has been recharged
So I don't worry about suffocating my fish even though I have little control ofer my CO2 dozing
I would, however, like to have a pressurized system like the Fluval 88 that I could control