I hang out with some discus breeders, the pH of the water for adults or growing juvies is fine out of the tap here, pH 7.7, harder water. The reason softer water with a lower pH is often needed for discus breeding has to do with the osmosis effect on the outside skin of the eggs. Harder water, having a higher mineral content, is actually better for growing healthy young discus.
Hardness stabilizes pH, most often water with a higher pH is also harder. Without knowing the hardness you may have luck with chemicals & tap water, it may come back to bite you.
Before even considering adjusting the pH of tap water you have to know as much as possible about your supply. Where does it originate from, what are the reasons for any changing of additives, do changes in seasons, agricultural practices, or weather have anything to do with these changes, a whole lot of questions. One of the best things you can do is contact your water supplier, get on a first name basis with someone knowledgeable who doesn't mind talking, and gather as much info as you can.