Good idea unless you like scraping you glass and scubbing rocks. Some people like the algae look on rocks. For glass, I've had good luck with young Chinese Algae eaters (both yellow and normal which is a grayish color). I would wait for the tank to build up a nice amount of algae and then drop them in. Two CAE's can clean a 75 Gallon up in two days. They are tough and can handle agressive africans (haps and mbuna). The problem is when they get big (5 or 6 inches) they get really mean and territorial. They can torture smaller africans and will interupt breeding acitivies.. You'll probably want to get rid of them after a while and pick up a some younger ones.
A better choice might be a good Algae eating Pleco. Do your research before buying one. Make sure it's a algae grazer. I have a med sized Golden Nugget (L001 in think) it is doing a great job on the glass. They get big though so you would need a 55 gallon minumum (which you probably have if you are keeping haps). I have dwarf clown plecos and bristlenose but they do not clean the glass too well.
If you have plants, then Siamese Algae eaters are the best to keep plants looking clean (ie jungle val and anubias which do well with african setups). You would need adult sized ones for your setup and they are not cheap.
As far as Ideal PH for these guys, I never worry about that. I keep them all in 7.8 (straight from my well) and they do fine.
Otos are great glass cleaners to if your haps are still small (they can be wimpy). If not they might be lunch. I have 4 or 5 in with my mbuna with no problems. An old established tank is always best for these guys (otos). In newer setups casualties are normal but survivors will thrive and do a great job of cleaning glass.