sorry to hear about your loss, unfortunately we all have to go through this at some stage.unfortunately, Oscars are very vulnerable to this disease. Has your other fish got it as well? anyway, the key to stopping fish developing hole in the head disease is regular tank maintenance. Oscars normally develop hole in the head disease when they are kept in poor water conditions for a period of time. Hole in the head is one of those diseases that may crop up even if you do keep your water in very good condition, it's one of those really annoying diseases that everybody fears. However, it is preventable to a certain extent, and more importantly, it is curable. There are various medications around that can be used. However, I would start off by regular tank maintenance, regular water testing and a healthy diet. If your fish has got this disease, it can often take a very long time to heal, it can also heal very slowly so you have to be very patient. if your fish has developed this disease, work out how many water changes you need to do so that your water is never above 20 ppm. This will depend on how many fish you've got, and how big your tank is.
just give it time, you may think that nothing is happening, then one day you notice that it is improving slightly, just keep doing what you're doing and keep your fingers crossed. Remember that severe cases of this disease can lead to very severe scarring so don't expect the area to heal completely over with no scarring.
