Ph is effected by many things...if your test shows it is at a bad level or does huge swings in then dont try to change it or fix it with out testing for the things that effect it....
Best to learn/research how temps, oxygen, alkalinity, calcium and other water hardners/minerals, ect. effect pH and test the levels of those things and only fix the ones that need fixing and in most cases this will keep the pH at a proper amount....Never try to buffer the pH directly without testing the things that can effect it first.
Reef buffer is primarly a Alkalinity buffer and if thats not the problem and you add it then it could cause parcipitation of other elements that can cling to glass like you are saying...Im not saying that is whats on the glass but......
IMO, best to just do regular well mixed and tested water changes with a quality salt mix and have good circulation in the tank and in most cases this will keep most levels at good levels....most cases.
If your goal is to have a reef, then knowledge about water chemestry is important.