I kept 4 adult discus in a 55 planted with large gravel, an UG filter and 2 times a month water changes in the early 90s, the fish didn't grow large but they did pair off and I had multiple good batches of fry that I sold to fish stores. Of couse I had 3 20 gallon tanks in my kitchen and was doing 75% water changes daily................so I quit (too much work)
Now I have a 125 with sand, and eheim 2217, ac110, and do 40% water changes every other day.................so, there are different ways of keeping discus for sure....................I'm with everyone, read, read, and then read again.............I will say, there isn't a single breeder, nor a single picture of a tank full of full size, nonstunted discus that i've seen where it wasn't on a very very vigorous water change schedule.