As others have said, a lot more information is needed here to be able to give a helpful answer.
In addition to answering the other questions asked above, what size are your discus, and what is your water change routine.
The number of discus you have, (and any other fish you have) how long you've had them, the size of your tank, what kind of set-up you have, and details of your feeding will all provide clues as to the problem.