I was thinking to drop the kh even more to 0,3 degree but at this level the ph would be stable at 5,7 with CO2 24/7. This is too acid to nitrifying bacteria survive, isn't it?
You are playing a balancing act. There is no doubt that bacterial activity decreases further away from pH 7.
https://www.epa.gov/sites/production/files/2015-09/documents/nitrification_1.pdf
But we need to question why. Enzymatic activity of things like Rubisco also doesn’t do as well at low 6s compared to 7 and 8.
The Effect of PH on the Rate of Photosynthesis
So why don’t we build a system to favor this? I’ve tried. It would have to mimic naturally entirely. Temp swings. pH swings up during the photoperiod - I’ve gone as far as run co2 only at night to favor Rubisco activity during the day. But you have to find a magical amount and that balance requires emotionally connecting with your aquarium in terms of fertilization, observation, pH fluctuations, temperature swings to force metabolism to skyrocket at those higher pHs - favouring bacterial activity ... fueling co2 ... fighting the urge to let that pH go up.
we are missing billions of years of evolution in our dirt. So we would need to lard so much co2 into the sacks of the tank and run enough light and temps to make enough sugar to fuel respiration at night. All this at the cost of potentially throwing the tank off balance.
the balance of what? The balance indicated by a feeing we get when we look at our tanks ... if we are happy, if is balanced.
why does co2 inject during lights on work? Because it’s a game of economics. Sure bacteria doesn’t work as well - but they still work. What works better? Lower KH. Better carbon assimilation at leaf interface? Soft water fish may favor the environment. Perhaps shrimp?
the larger picture is determine what is it that you are catering to in your tank. And will that cater destroy everything else so much so that you are unhappy - not the forum ... no one cares about what I think about your tank.
24/7 inject of course will work. It means that you have maximum capacity to your injection rate in those plants sacks at lights on and the pH is at this “level” that is sound for everything.
is pH stability that important? Why? Enzymatic function? Bacteria? If so, we know that at some point pH should be higher to favor those ... along with temperature. But then you have to futz around with another timer? Keep it simple. It’s a trade off.
Try things . No one is an authority over your hobby.
Josh