Oscars with Hole In Head

#1
I have 3 oscars, one dempsey, 2 plecos in a 220 tank...my 2 elder oscars (about 6 years old) have pits in their head, and the younger 3 year old albino has newly developed pits...I have heard of HIH but the elder oscars dont have character changes and have had it for 2-3 years...can anyone tell me if I need to worry about HIH or if these pits are just age pits? If I do need to treat for HIH, how do I treat with such a big tank....aggressively with medicaton or just water changes?