Hagermanfd - When you see someone recommending changing 50% water a day for discus, more than likely it is because they are feeding raw beefheart mix. Leftover beefheart mix is highly recommended as a key food for growing young discus out. But leftover beefheart will foul your water in a blink! Think about it, not flakes, but rotting beef in 86 degree water. And discus breeders do this a couple of times a day. That is also why they recommend barebottom while you are growing them out. The staple for my discus is frozen bloodworms. My discus weren't nuts about beefheart, so I stopped feeding it. I do two 50-60% water changes a week on my planted 72G. I have a measure of about 7 nitrates coming out of the tap, higher in the summer when fertilizers are running off. I'm changing the water more to lower the nitrates after a couple of days, there's never any leftover food in the tank! Discus are very sensitive to nitrate levels. And it is true, you need to feed juvenile discus 4 to 6 times a day. Adults 1-2X. If you overfeed during those 4-6 feedings, your tank water quality is going to go down real fast.