Proper maintenance of your tank and fish includes keeping a healthy and clean environment. You need to do regular water changes,, cleaning the gravel, rinsing/cleaning the filter media, removing any dead/decaying material (fish, plants, food), and monitoring the water temp and chemistry. It is vital you know at least the pH, ammonia, nitrite, and nitrate levels. Keeping your water in proper balance can help to avoid disease and fish loss. You may be able to detect a problem and correct it before your fish become ill or die. Invest in a water testing kit.