Keeping angelfish and discus together seems like a natural mix. Both are spectacular fish and the temptation to put them in the same tank is compelling. Both species come from the same area and live in a similar environment. Angelfish and discus are good candidates for blackwater aquariums. However, whether they can live together in an aquarium depends on several things and which aquarist you listen to.
Angelfish and discus are both cichlids. Cichlids have the deserved reputation of being aggressive and unable to live with other species. Discuses are shy and timid, angelfish are generally peaceful but can be territorial, nippy and an aggressive feeder. Both become territorial and aggressive when they are raising young. This should be enough to keep them apart, but some aquarists have kept them in the same tank.
Discuses do better in a big aquarium, and a 40 long is considered a minimum size tank for them, and bigger would be better. This is especially true if the aquarist plans to keep angelfish in the same tank. This gives room for them to grow and school. They like plants, so the tank should be well planted and have wood such as Mopani or Malaysian driftwood to provide places for them to hide.
Lore is that a discus can easily acquire a disease from other fish. Aquarists that have experience with the species say this is more the case with wild discus, and domesticated stock is somewhat more disease resistant. If mixing angels and discus that are captive bred disease might not be as much a problem. Captive bred angels don’t carry diseases like their wild relatives. If mixing the two, keeping an attentive eye on the tank for disease is required. Learn more about discus health with this book.
Water quality is important for any discus keeper. Discus like clean acid water and angelfish will adapt to discus water rather than the other way around.
The water should be slightly soft and slightly acid. Softness should range between 13 and 15 dH and the pH should be between 5 and 6.5. Peat is a good way to control pH and soften water.
Monitor the number of fish as they produce nitrates, phosphates, ammonia and hardness will kill a tankful of discus in short order. Frequent water changes will keep this under control. Keep the temperature steady between 82 and 86 degrees.
Using a large tank with lots of plants or other cover, frequent water changes, proper water temperature and condition are needed for discus to thrive. Those are the conditions where angelfish and discus may survive together. Even with perfect conditions, there is no guarantee they will live together successfully. Without perfect conditions the chances are less. Some aquarists have had success mixing the two cichlids, others not.
*Top photo by V.v, Flickr