Discus Fish are not cheap and you want to make sure that you have a healthy fish when you leave the pet store. Here are some things that you want to look at before you even purchase them. The first thing is the obvious and that is picking a fish that looks healthy. It is a good idea to watch them swim around for a while to see if they are showing any signs that they may indicate that they are not healthy. It is also a good practice to look at any labels on the fish tank that might indicate that there has been sick fish in the tank. The label would have DNS on it and that means that the fish could have been quarantined at one time. Discus fish has a round shape body in nature and when buying discus fish you want to make sure that you take a look at their shape. This could show that they have an illness. Over the years I have learned that by looking at discus eyes can tell whether they are healthy or not. Their eyes should be clear and small. If you are looking at a discus and their eyes look dark, huge, or cloudy that could be a sign that they are stressed or have an illness.