So if you plan on buying a smaller tank know and just upgrading to a bigger one later on, you may find that this would be futile. You would just be spending more in a short period of time. A small tank will just stunt their development and will stress them out. But also remember, if the tank is too big, the young discus fish can become overly skittish and can also stunt their growth. This is why larger fish tanks are recommended for discus fish. The smallest size for at least 6 discus fish would be a 40 gallon tank. When you get a new discus fish, you have to quarantine them before you place them on your main tank. This is to prevent them from introducing bacteria, parasites, as well as other types of diseases that can be transferred to other fishes inside the main tank. If you don t know anything about the nitrogen cycle, then you may want to cancel your plans on keeping a Discus Fish. You have to remember that Discus Fish will not tolerate ammonia or nitrite in any amount. They will only be able to tolerate the bare minimum nitrite. You also need to make sure that the detritus is removed on a daily basis along with any uneaten food as this will produce ammonia in the water, which will potentially make the Discus Fish ill or possibly kill it. If the keeper says that they just fed the fish, then you should look for another place to buy a Discus Fish. As much as possible, you should buy an adult Discus Fish. This is highly recommended for first time owners of Discus Fish as adult Discus Fish costs lesser to maintain than juvenile ones. You need to remember that juvenile Discus Fish are far more sensitive to water quality and food quality than adult Discus Fish. Discus fish are easily frightened and if they have nowhere to hide, they will get stressed easily and can possibly hurt themselves from dashing around the tank and hitting the glass. The water is also an important factor. Make sure that you keep the pH level of the water at 6 and also the temperature at a constant 82 to 86 degrees F. A partial change will also be good and it will require less handling of your fish. Changing at least a quarter to half the water in the tank will suffice as long as you have a good biological filtration system installed. In some cases, some aquarists would just add some medication to clear up the dirt.