Well I have a horror story for all those who inject co2. Sometime in the middle of last night my co2 diffuser popped off the co2 tubing. Which then let the full pressure of the co2 pump unhindered into my tank. Well the ph dropped from 6.8 to somewhere under 5.0 and all my fish were dead! 2 discus, some 20ish tetras, twig cat, 3 blue rams and 1 bamboo shrimp. DEAD!!!!!
I know it takes a long time to saturate the water with co2 but its not worth the risk to let it run 24/7.
Well I guess you live and you learn.