Glad they're doing better. I (very successfully) kept discus for years and my observation is discus care is ultimately very subjective. What or what not to feed, plants or no, substrate or bare bottom, size and frequency of water changes, water conditions, compatible tankmates, preventive medication or no, the list goes on of debates over keeping discus. So, I hope you don't mind a few comments on water changes, as far as why you might get different recommendations. Not at all implying you don't know what you're doing, it's just my take on it.
Lot of people think you absolutely must do it this or that way, but the reality is there are different approaches and more than one way works. Water care with discus comes down to one general principle, which is they do best in very clean water with low nitrates and other organics. How you achieve that is where there is no single absolute rule you must follow. Bare tank, feed with beef heart, heavy feeding, and/or generally heavy to excessive protein levels and, yeah, you should probably do daily heavy water changes. Larger tank, biologically balanced (between substrate, periphyton on driftwood or other surfaces, plants, nutrients, etc.), more moderate feeding and protein levels, and other factors can mean healthy discus with fewer water changes. The result is you'll get varying recommendations and there are too many variables for there to be a single cosmic rule everyone must follow, just different philosophies and approaches and it can depend where you learned your discus care (which book, which forum) what you think is the 'right' way to do it.
Not going to write a book here or delve into all my personal philosophy on discus keeping, but here's one basic fact-- the approach of some people feeding them is unbalanced and can increase the need for water changes, which is basically that they overfeed and especially overestimate their need for and overfeed protein. Study finds discus fry grow fastest up to 50% protein levels, above which they grow slower. Growth difference between 45-50% is small. This is comparable with other omnivorous/carnivorous species; for example it's a little lower than some trout species. But some people go overboard on their protein requirements. The connection to water changes is excess protein means poorer assimilation and ultimately excess nitrogen waste, therefore more water changes needed.
I'm not at all saying everyone who does a lot of water changes is feeding wrong, etc. What I'm saying is the balance between feeding, protein levels, source of protein, tank ecology (including everything about the tank, size, filtration, plants, algae and periphyton, etc.) ultimately affects water quality and what you actually need in the way of water changes. So for one type of tank or approach you might really need daily, large water changes, but it's not some cosmic law that applies to all discus tanks or all discus growout tanks.
