Honestly, I do not think 7.2 is a problem. Most fish are really good at adapting to a stable pH, so I think its fine. I belive peat moss should help lower it, but if I was you, I wouldn't be concerned. Gbr can be crazy sensitive, so if you are keeping them without a problems, thats a really good sign.
If you do want to try to lower it, you can put a bag of peat moss in the filter by the out-put so it lowers the pH and circulates it through the aquarium.
Yeah, that is pretty high ammo in the tap water, but you already know to use Prime, so I think you are ok. And the .25 reading isn't harmful to the fish.
, you are ready for discus.
Like I said, if you have been stable enough to keep neons and gbr, then discus should be ok.