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.
If you're going to change your PH level, I'd change the base and not chase the drop. The 2HR aquarist spread sheet on what PH level drops are needed vs PH/KH levels. You can find it HERE
Tbh with you, I myself have stopped chasing KH and PH levels. I run tap water on my 2 tanks currently. I used to remineralize RO water and eventually gave up. Also Sodium bicarbonate (baking soda) will raise KH/PH on the cheap.