Many people like to think that it is easy to find compatible fish to go with their discus. However, this is not the case. Discus fish can be quite particular about the other kinds of fish they let into their inner sanctum, if they do at all.
Many discus keepers, who keep their discus for show, argue that having other fish is crucial for having a breathtakingly spectacular show tank. The fish of choice amongst these discus keepers is some cardinal tetras. These fish only grow to be about 3 centimeters, so they are not a threatening presence for the discus. Much like the discus, cardinal tetras prefer the water warmer, but not too warm. It can be quite a trick keeping the temperature suitable for both your discus and the cardinal tetra. What’s slipping into the lower ranges of being comfortable for a discus, is slipping into the higher ranges of what is comfortable for a cardinal tetra. The cardinal tetra is a very social fish as well, so if you do decide to have some swimming around, you will want to make sure you have at least six of them as well.
One of the reasons it is difficult to keep other species of fish, even the cardinal tetra, in conjunction with discus is that they are a rather gentle species and can be intimidated easily.
Another reason it is difficult is that some species of fish can carry parasites their entire lives without having a problem, however those same parasites could be devastating to your discus population. It is always important to remember that you will want to have any fish you are planning to integrate into your discus aquarium stay for at least two to three weeks in quarantine, just to make sure they don’t have any health issues that could potentially be harmful for your discus.
Some other fish which are compatible in the discus environment are; Congo, Lemon, Glowlight, Neon, Emperor, and Penguin tetras; apistogramma dwarf cichlids; and ancistrus, corydoras, and otinculus catfish. The later are especially useful when it comes to helping to control any algae which may manifest itself in your discus aquarium.
A couple of examples of fish that are not compatible with discus are angelfish and any nocturnal fish.
Angelfish are not a good idea to have coexisting with discus as they are a rather aggressive fish, and if left to their own devices, they will bully the discus and beat them back, and basically take over the tank.
Nocturnal fish are not a good mix for discus as these nocturnal fish will swim around and disturb the sleeping patterns of the discus, and this could cause them great stress, which could result in some serious health problems for them.
If you are just a beginner and really have not done your research it is not advisable to add other fish to the discus’ environment, as even seasoned hobbyists have trouble integrating other fish into a discus society.
The best thing to do if you are going to be raising discus, is to just keep discus in the tank, as throwing other fish into the mix can be quite troublesome.
As you can see show tanks require much more maintenance than breeding tanks or growout tanks, so it is important to take that into consideration before you decide if you want a show tank or not.