Originally Posted by hoppycalif
In a fish only tank there is no CO2 injection to make the pH change. In fact the pH should remain virtually constant unless something generated in the tank makes it change.
What do you think fish do? They inject CO2 into the system.
If you are saying that CO2 is removed from your tank by aeration, this is true. But the rate is very slow compared with the rate consumed by plants (at least in my aquarium).
Here is the point. You can make up any story you like, but have you used a pH controller? I have. Now it may go on at night without me knowing about it but whenever I've looked it was not working and the pH was constant.
During the day it is basically on all the time.