After two years of trying, I still found it impossible to maintain the Co2 level in my 100g tank. Although I tried turning the Co2 on 4 hours prior to lights on, I still wouldn't reach any target consistently several hours after lights on. Only after installing a Ph controller more recently have I been able to maintain the tank without turning it into a BBA zoo.
So I then set the needle valve to maintain my target Ph (6.15) throughout the day running open (so as not to turn off the Ph controller). This worked really well except in the morning I discovered that as before, I couldn't arrive at the desired Co2 saturation level at lights on unless I started many hours prior. For whatever reasons that I can't discern, the tank requires a Co2 boost initially to bring it up to speed. Once there, it can be maintained with a much smaller amount of Co2 being injected quite readily.
If I am to be able to break from the Ph controller dependency, my solution (which I hate because these things always cost more money) is to install two solenoids, and two valves each running on a separate timer. One to be run more open for one hour to achieve the desired level, and another to take over and run open throughout the remainder of the day to maintain it.
I guess my question is this how it's done for large tanks, or am I injecting too much Co2 or? The fish are fine and things are really growing like mad and I couldn't be more pleased. No reason really to mess with it other than to lose the Ph controller. I could always dose less Co2, I just don't want to deal with the algae again now that things are going so well.
I've got good flow running around 10x overall and good mixing etc. Running Eheim 1103 NW w/venturi through Nu-Clear canister. Separate 300g pump pulling through internal trickle filter (sealed)