Terry, I have about 3 years experience caring for and breeding Discus.
I used to do small water changes daily on my display tank but I do believe in my case it was a waste of time (I had plenty of Filtration). I think a weekly water change of 10-20% is just fine even with a moderately stocked tank with plenty of Filtration.
During the Summer I would let the water sit in the Sun for a couple of days and during the Fall I would collect rain water. Wish I had used RO/DI
water back then.
Any other questions, fire away
.