I have a water softener, and I go after the softener, from the tap.
I found not having to worry about any chlorine/chloramines, or any bad stuff makes it heaven doing a water change.
I would much rather add epsom salt than worry about adding prime to detox the very water I'm adding to the tank.
My wife doesn't have discus, but she does have angels and while it hasn't been a perfect run (we've lost 2 in 6 months, but I think I scared one to death and I think the other was bullied), all 9 aquariums seem to be doing very well.
That being said, we don't have any live plants in our tanks. I tried raising anacharis (who can't do that?) but it kept dying off. Could have been the temp though; I heard it only likes colder water and it was in 80°F.