PH issues

Without knowing you KH, it's hard to say what's going on. On the surface, it sounds like possibly you don't do water changes quite as frequently as needed to maintain a stable KH, so the buffer gets burned through by the normal biological processes in the tank, allowing pH to dive...Then you do a water change, which replenishes KH temporarily and bounces the pH back up. Doing mroe frequent water changes would help, but if the KH of your source water is very low, you may need to supplement.

How long had the tank gone without water changes? I know I tested my pH one day and it was doen close to 6 but 7.4 out of the tap. I upped my water changes to 20% from 10% and it is now much more stable. My gh and kh are fairly low so biiger water changes are needed to keep that pH up.

If I were you and this happened again I woudl suggest small water changes over a longer period of time to get the ph up and stable. The sudden shift is far more harmful to the fish.

one time i had some tanginikans, i added proper ph 8.2, so the water went from around 7 to 8.5 in a day, they didnt seem to care hehe

some fish realyl really tuff, i put a guppy from a cold water bowl to a 82 degree saltwater tank, and its doing great i would not worry too much... i dont even know how a fish senses ph anyways

Funny you should be talking about this, cause just today I had a near disaster with pH.
I was doing my weekly 50% water change, with my Python no spill. and wasn't paying a lot of attention. When I got it filled again, I noticed the water was yellow.
What I DIDN'T know was that they were working on the water lines out in the street. I dont know what the hell was in the water to make it yellow, but my pH dropped from 6.9 to 6.0.
I very quickly added some baking soda and some Seachem Clarity (its supposed to clear out **** near anything). Anyway,
it seemed to work. This happed about 8 hours ago, and my pH is stabling out to 6.8, and the yellow is gone.
So far the fish seem fine. I've been watching pretty close, but I don't know if a pH change like that would show up right away or what.
Guess I'll know in a day or two.

See Ya

Sounds liek a bunch of iron or tannins got into the water. Probably wouldn't hurt the fish directly but the drastic change in pH could have. Good thing you watched the tank so closely.

Yeah, I was lucky. It's been about 24 hours now, and still everything seems AOK.