Re: when to turn co2 on
I can afford any pH device I want as well as for my clients, I do not use them and have had issues with them in the past.
pH is not the issue regarding fish health, the KH/GH is.
pH varies up to 2-4 units in heavily vegetated shallow lakes, every day.
Fish do well.
Adding CO2 is not the same as adding baking soda(this can kill fish) a full pH unit.
Here is the death blow regarding pH swings being bad for fish(any fish or plants or invert): what happens when you do a large water change every week?
My tap water pH is always much different than my tank water pH, most folks have a difference of 1 full pH unit, about the max amount CO2 will do at the levels we add it. I typically change 50-80% weekly.
Fish love it.
Been doing this with CO2 for 15 years.
You do not need CO2 at night, there is no use for it.
It might be conveinent (sat feeding it into the filter intake), but other than that, there is no use for adding CO2 at night.
pH swings have no impact on biota from CO2 differences.
Regards,
Tom Barr