Originally Posted by SlabSided
The water out of my tap is 7. However, once it goes in the tank with the gravel and rocks, it goes up to 8 (not sure how long it takes to do so). So every time I change the water, even a partial change, there is going to be a fluctuation. Is that going to cause undo stress? Or will he get used to that too?
No, I wouldn't worry about that, either. When you do a full change, he gets re-acclimated. And for partial changes, the KH in your water will buffer fluctuations, as well. So, when you add more water with a slightly different pH, it'll be so diluted down between mixing with the other water and the KH buffer that it isn't going to cause a problem. And, because of the small concentration, he should adjust to it easily. Same as when you remove a bit of cup water and add some tank water while acclimating a fish.
And honestly, the most important thing to be stable in your tank, even above pH, is KH. For example, in some tanks with CO2 injection, pH can fluctuate between 6 and 8 over the course of a day, but as long as the KH stays stable, it does not cause a problem for fish. Your KH will remain stable with water changes, as long as you're always using the same source water.