pH Levels.

Jaden wrote in :

Hard water area, pH from tap 7.1 - 7.2
....
My tank pH seems to settle at about 7.5 - 7.7. I have treated it
previously with a pH down (Aquafin) solution - making it 7.2 or so, but
the next day, it will climb again. I don't think this is the end of the

I wouldn't concern yourself with your pH too much.

But since you asked, your water likely contains high quantities of
carbonate, probably calcium carbonate, as hard water sources often do.
Carbonate is an alkali and will neutralize acids such as pH down leading to
pH rebound after dosing.

If you want to lower your pH (again, I wouldn't worry about it in most
circumstances) you will have to use an acidifier that will neutralize your
carbonate levels. Seachem makes a product called Acid Buffer which will
convert carbonates into carbon dioxide. It is one of the easiest way to
lower pH in hard water environments without resorting to something like
reverse osmosis water.