How long have you had your tank set up? Most fish appear to be doing fine initially, but as the tank matures, you will see a lot of changes. Basic water test kits are not enough for Discus. You have to know parameters like conductivity, total dissolved solids, hardness, phosphate and trace element levels. Iron is fine, but Discus are sensitive to phosphates. Additionally, many prepared water conditioners like rightstart, start right, Amquel plus and prime contribute to conductivity and TDS. The only prepared formulation that does not significantly affect these parameters is Amquel basic....not the plus. A good place to go for the skinny on water quality and hand raised discus (not from he big box stores) is aquaresearchcenter.com. There is a lot to learn, but Joe Gargas taught me volumes about water quality and the dangerous overuse of chemicals. Since I adopted his methods paired with the additional knowledge I gained from Rivercats, my plants and fish are thriving. I have about 26 Discus babies and adolescents and have not lost even 1.