I wouldn't adjust anything. PH is a fairly good indicator of how much CO2 you're injecting. Many hobbyists here , including myself, have had no problems with a PH drop of 1-1.5 from our base PH due to CO2 injection. My PH drops from around 8.1 to 6.9~7.0 during peak CO2 injection. I have Endlers/Guppies, ramshorns and cherry shrimp in the tank and they're doing good.
And yes if you have your CO2 on a timer. Once it turns off, your PH should rise back to your base PH due to degassing of CO2 out of your tank.
Thanks for the answer. It's hard to see how that kind of daily pH swing is good for plants and animals but clearly lots of people are doing it with no ill effects and no funky algae forming so who am I to argue!
My other question is, does the buffer (if I use one I'll be using Seachem Alkaline) just change the 'begin' and 'end' pH by the SAME amount or does it decrease the "spread"?
I have 7.4 pH nominal water that goes to 6.6 pH @30ppm (after CO2 injection). If I add a quantity of buffer to change my 30ppm pH to 6.9 will that make my nominal water pH 7.7? (both high and low offset by +.3 pH?). So with buffered water, I would go from 7.7 pH nominal (no CO2) to 6.9 pH @30 ppm? (assuming I target an amount of buffer to get to 6.9 pH @ 30ppm).
Is the buffer's action completely linear? Apologies that I don't know how to ask this clearly. Just some places I read state that a buffer will HOLD a specific pH until the buffer is fully utilized, and only then does the pH start moving. So they seem to imply for example, if you add buffer to a 7 pH water source, it will then stay at 7 "more resiliently" until you add enough acid to counteract the buffer, and only then does pH start to fall. I'm trying to understand how a buffer behaves.