Yup thats a dolphin moori which I'm growing out to put into my 125. The tank its in now is full of south American tetras/zebra dainos. I guess since the fish are fine I'll just not worry about the pH.Usually pH does the opposite in tanks.
But since the blue fish in your pic, looks like a rift lake African, I'm not sure why you are worried about the pH.
The rift lakes can sometimes have pH to almost 9.
If you are worried about pH stability, you just may want to do more frequent, smaller water changes per week.
That makes a ton of sense. After a water change there are always a lot of water bubbles everywhere.+1. The rock look like basalt. Non-reactive. It's likely that your tap has some excess dissolved co2, which lowers ph. Once it goes in to the tank, the co2 gets gassed off and ph goes up.