Even seemingly minor pH swings can be very stressful for discus, especially if those swings are rapid. Since a pH change of 1 is a change to the power of 10 (i.e., 1 until is 10x different, 2 units is 100x different), then your tank jumping from as low as 7.0 to as high as 8.0 is a significant swing. If that swing is happening as rapidly as a water change, then that could be quite a shock for discus. Some fish might be able to endure that kind of shock, but I would worry about its effects on discus.
Have you considered an RO unit? They aren't practical for everyone, but they can definitely solve water quality issues in source water. I know some people filter through peat to lower pH. I haven't tried that method so I can't speak to any potential pitfalls of that method.