I have really soft water. I really, really hoped I wouldn't have an issue with pH, but in the past week, my pH was at 7.2 before and after a water change, was at 6.8 two days later, then between 7.0-7.2 two days later, between 7.4 and 8.0 two days later, and after a little water change and new decoration(s) is down to 6.6. I'd blame the new decoration or water change, but the pH went down earlier in the week, and not after the water change... My tap water's pH is between 7.2 and 7.6.
This in a 10 gal. filtered, heated, cycled. Ammonia and nitrites are zero. Nitrates were always 0-5ppm. There's a few floating plants (wisteria, java fern, mondo grass), gravel substrate, and one wee betta fish.
So far, Iv seems his usually self. I know maintaining a constant pH is important--versus what that pH is.
I added one Jungle Correct pH only because I kinda freaked at the 1.0 swing, and it says it buffers
the water... and I had some on hand...