In my experience ph really doesnt matter with domestic discus. The only real parameter that you have to worry about is hardness. Discus will need softer water if you plan on breeding them. The harder water causes the eggs to calcify making it so the fry cant emerge from the egg. I keep my discus in a ph over 8 and all do great, I even get them to breed in that ph. The most important thing is to keep the water clean. With all the water changes that have to be done with discus it would be insane to try and change the ph and keep it constant. Another thing with discus and ph is that some of them can be sensative to the ph change with water changes. Almost all the time there is some fluctuation with ph when a water change is done, thats why you hear of people aging their water...to remove the chlorine and to stabalize the ph. The reason why the ph changes in the tank is because the natural CO2 in the water gets driven off and causes the ph to rise. Like with mine the water comes out of the tap at 7.4 but a few hours later it jumps up to roughly 8.1. Your discus will be happier with a stable ph no matter what it is.
I also agree that you should avoid LFS discus at all costs. You never know what you are introducing into your system when you do that, especially if you already have discus.
