The worst thing that can ever happen is that you purchase new discus fish, put them in the tank and they infect the entire tank. When you first purchase new discus from the pet store, you should have a quarantine tank setup for them. They should stay in the new tank for at least one month and you should observe them for any diseases. You will need a 10-20 gallon tank, filter, heater and light. You do not want to add any plants or gravel. You want to observe how they are eating and what color is their feces. Healthy discus fish will start to eat once food is introduced in the tank or if they don’t eat they should at least acknowledge that the food is there. Their waste should be black in color. White waste is an indication that they are infected with parasites or disease. You should also observe them to make sure that they look healthy.