My discus health book says that hole-in the-head is most often a
dietary disease. which shows up when discus are lacking calcium,
phosphorus, or vitamin D. However, the deficiency itself can be caused
by an intestinal flagellate infestation that makes it difficult to
absorb nutrients. Try feeding vitamin enriched food, good flakes or
pellets (just look at the ingredients label). I like new Life Spectrum
Discus Formula. If that doesn't help you can try treating for
parasites. Try medicated food instead of treating the whole tank,
either pre-made, or regular food soaked in medicine (you should look up
the correct procedure for this). I hope this helps.