Day or night for 2 part?

[BradB]

I've been dosing 2-part (Sodium Carbonate solution) evenly over 24-hours and switched to a Neptune DOS and programmed it to only dose when the lights are off. This stabilized my pH, which I assumed was a good thing.

Thinking through it more, pH only drops at night as there is more CO2 in the tank. When the lights come on, CO2 is photosynthesized which raises the pH. Logically, I'd assume Alkalinity rises and falls opposite pH - high pH and lower Alkalinity at the end of the day, low pH and high Alkalinity at night. So by dosing at night, am I increasing my Alkalinity swing? The opinion on the Internet seems to be that Acropora is more sensitive to Alkalinity than pH, so wouldn't it make more sense to dose during the day? I could switch to Sodium bicarbonate and dose during the day to level my pH as well, although that would give me lower pH overall.

 

[Randy Holmes-Farley Verified Community Expert]

If stabilizing alkalinity is the goal, dose during the day.

If stabilizing pH is the goal, dose at night.

I'm not sure there is convincing evidence that either is better than the other.

 

[bobnicaragua]

I dose kalk continuously and two part every 3 hours.

The best thing I did for PH was crack a window. It’s a tiny crack, barely visible, maybe you could slide a dime under it.

Alkalinity consumption increased and coloration improved.