Hole-in-the-Head HITH is associated with the parasite Hexamita. This is an internal parasite that lives in gastro intestinal tract of the fish. As mentioned the best prevention is clean water ie 50% a week min and a healthy diet. If the fish gets HITH drugs like Metro work alonge with increased levels of vitemin C have been effective in helping the recovery process. The best prevention is a clean healthy environment and well balanced diet, which can be provided by a high quality pellet, NLS Thera +A is an excelent choice. Do not feed live fish that have been purchased as feeders from a LFS. Keep the nitrates as low as possibile, test your tap water so you have a base line to compare your tank water against. Use a declor such as Prime at each water change. If your diligent in your maintance you sould not have an issue.