You will be able to tell that which pair is the mating pair. Discus Fish will establish territory within the aquarium and you will see them defending it against the other fish in the tank. This means that they are getting ready to breed. You have to keep an eye on the mating pair as you will need to move them in to the breeding tank. However, before you start to attempt raising discus fish, it is important to know that discus fish can be quite hard to keep especially for people who are just starting out in this kind of hobby. You need to remember that discus fish are temperamental creatures that need special care. They are very sensitive when it comes to water quality as well as food quality. While they are still young, it is virtually impossible to determine its gender. Also, be warned that over handling the fish may result to its death. So you need to have a very keen observation so that you will be able to truly determine the sex. You will need to be very patient and to follow the fish well, for those who do not know the differences between the male and the female, it would be very hard to discover its gender. Also, you should observe their behavior. If your discus fish go on food strike, it s a clear sign that they are unwell. The color of their scales will also get darker, which is also an indication that the discus fish is sick. These are some of the things that you need to understand about discus fish. When they reach adulthood, you will soon observe that if there is indeed a pair, both of them will soon claim a space in the tank, and start protecting it. This pair will then be your breeding pair. Have a breeding tank ready as soon as you discover them. A breeding tank should be separate from the main tank so as to protect the spawn, at the least; your breeding tank should be 20 gallons. Aside from the flakes and granules, feed them blood worms or fresh or frozen brine shrimp as discus fish are carnivorous. Keep your aquarium in a quiet and solitary place. Too much noise and motion, like a door opening or heavy human traffic can cause them stress. Never overcrowd your tank. Discus fish are very protective of their space so they need an ample re to grow and breed.