You can use a product called HOLE-N-HEAD GUARD. But you have to be diligent about making sure you take better care of the water and living conditions or it will be all for nothing.
Also known as: Head and Lateral Line Erosion Disease (HLLD or HLLE), Lateral Line Erosion (LLE), Lateral Line Disease (LLD).
This disease is especially common in discus fish and Oscar fish and causes large cavities and soars on the head and along the lateral line of the fish. The open wounds caused by hole in the head disease are very distinctive and makes this disease easy to discover and diagnose. If your fish has growing wounds on its head it is likely suffering from hole in the head disease. Early signs of this disease are small pits on the head of the fish. This disease often appears simultaneous with a disease called Hexamita and this has lead to these two diseases being frequently confused with each other. Hexamita attacks the intestines of the fish and can often be the cause of the hole in the head disease which has been attributed to nutritional deficiency, The two diseases are however not one and the same.
Hole in the head disease is believed to be the result of a deficiency of one or several of the following nutrients: Phosphorus, Calium, Vitamin C and Vitamin D. This deficiency can as earlier mentioned be caused by Hexamita and its effect on the digestive system but it can also be a result of poor water quality, poor diet or over filtration using chemical filtration.
Hole in the head disease is often very hard to cure, especially in its later stages, but an improved diet with more vitamins and increasing the water quality by cleaning the tank and performing more frequent water changes might help. It is also recommended to remove any chemical filtration such as active carbon filtration. Improving the diet of the fish can include adding vitamins to the diet, introducing vitamin rich flake food to the diet and removing (or at least cut down on) nutrient poor feeder fish and beef heart from the diet.