I think my tank has old tank syndrome, has been setup for ~4 yrs, 55 gal. I am trying to figure how to increase the pH. It's currently at 4.5-4.9. Added 4 - 6 cups of coral in wet/dry and over 48 hrs, has not changed. Ammonia, nitrate, nitrite all reading at 0. It's probably 50% covered with plants. When I noticed the low pH last month, tried vacuuming gravel when doing a WC, but then noticed the ammonia went up, so figured I must be getting rid of good bacteria, so this current time around, only removed water not via gravel, but pH did not increase. Fishes currently in there are 29 cardinals (1+ inches), 5 pristellas, 6 rasboras, 2 3" clown loaches, 5" bristlenose, newly added panda cories (did lose 3 out of 8). Healthiest are the tetras. Nothing is really listless, loaches were, but now have their colors back.
So, my questions are: do water change via vacuuming gravel or only water at mid-level? Add additional coral until I see start of increase in pH?
Thanks for inputs.