10-50% water changes once a week with 2" in fish WILL result in stunted discus and you will probably experience disease and sickness JMO...
True, with some tank setups and methods of feeding, but otherwise-- not necessarily.
I've grown out a lot of discus from from 1-2 inches, wild and domestic, and for me they generally reached 7-9 inches, depending on gender, variety, and individual fish. Never had them getting sick on me, only sick ones I ever had were ones that were sick when I bought them that I tried to rescue (successfully, I might add, with all but two that were emaciated when I got them and didn't last more than a week or two). Two things I never did was keep them in bare tanks or feed beef heart. My discus tanks always had plants, some more than others. I've kept them in ph anywhere from 5.8 to 7.6. Only once did I keep them without other fish. I've done water changes anywhere from every other day (low ph tanks) to once every 4-7 days for young growouts.
The point is they do best with clean water, low dissolved organics (aside from plant based tannins, etc.), low-ish nitrates and good nutrition. But there is more than one way to get there (and I've done it more than one way). Doesn't always have to mean bare tanks, no plants, and lots of water changes. A lot depends on what and how much you feed them, like a lot of other fish. How
much you need to feed them to get good growth also depends on
what you're feeding and how efficiently they process it... and while beef heart has been debated to death, what I
know-- from experience
-- is they don't
need it to grow to a good size. There are other good growth foods, plain and simple, and my
opinion (and experience and research) is in reasonable amounts they can reduce tank maintenance.
In addition to the above references, here's another one relevant to this post:
Ideal protein.