top-off water

[mark]

If you are using ro/di you'll find the pH right from the output is less than 7.0 (think I measured 6.8). If it's aerated it will become more neutral, so ideally one would aerate for a day before adding to lessen the pH swing.

That being said, I'm not and my pH is steady but then I don't have much in the tank nor evap'ing much either .