Discus fish care guide: water parameters, tank size and tank mates

01

Discus fish care: what you are signing up for

Discus are round, flat South American cichlids, and the colorful strains in stores (Blue Diamond, Pigeon Blood, Red Turquoise, Leopard and many more) come from decades of selective breeding in Asia and Europe. Most discus sold in the US today are tank-raised, which makes them more tolerant than wild fish, but they still need far more consistent conditions than a typical community tank.

Three things define discus keeping: heat, clean water and a group. Discus are kept warmer than most tropical fish, they react badly to dissolved waste, and a single discus or a pair in a big tank is usually shy and stressed. Start only once the tank is fully cycled, and buy all your fish at once from the same source if you can.

• Group: 5–6 discus or more, of similar size
• Tank: 55 gallons minimum, 75 gallons or more recommended, at least 18–20 in (45–50 cm) tall
• Heat: 82–86 °F (28–30 °C), stable day and night
• Water changes: 30–50% at least weekly, more often for juveniles
• Quiet location: away from doors and heavy foot traffic

02

Origin and natural habitat

Wild discus come from the Amazon basin in Brazil, Peru and Colombia. Scientists currently recognize three species: Symphysodon discus (the Heckel discus, mainly in the Rio Negro area), S. aequifasciatus and S. tarzoo, though the taxonomy is still debated. Most aquarium strains descend from crosses of these forms.

In the wild, discus live in slow lakes and flooded forest connected to rivers, sheltering among fallen trees and roots. The water is warm, very soft, acidic and often stained brown by tannins, with very low mineral content. This is why wild discus need soft, acidic water, while tank-raised fish have adapted to a wider but still soft-leaning range.

03

Adult size and lifespan

Adult discus reach 6–8 inches (15–20 cm) in diameter, and large, well-grown fish can exceed that. Size depends heavily on how the fish was raised: stunted juveniles kept in poor conditions never reach full size, which is one reason to buy from a reputable breeder.

With good care, discus live 10–15 years. Like the angelfish, they are a long-term commitment, and the effort put into their first year (growth phase) shapes the rest of their life.

04

Discus tank size

Plan about 10 gallons (38 L) per adult discus as a rough rule. A group of 5–6 adults needs at least 55 gallons (208 L), and 75 gallons (284 L) or more is easier to keep stable and leaves space for a few tank mates. Height matters because discus are tall: aim for at least 18–20 inches (45–50 cm) of water. If you are choosing a tank, see our guide to the best 55-gallon aquarium.

Many breeders keep discus in bare-bottom tanks because they are easier to clean. In a display tank, a thin layer of sand, driftwood and heat-tolerant plants such as Amazon swords, java fern and anubias look natural and work well, as long as you keep up with siphoning.

05

Discus water parameters

Tank-raised discus do well in soft to moderately soft water with a pH between 6.0 and 7.0. Wild discus and breeding pairs need softer, more acidic water, often prepared with a reverse osmosis unit. Stability is the real priority: a constant pH of 7.0 is better than a pH that swings between 6.0 and 7.0. Our guide on how to lower pH explains safe methods, and the aquarium water parameters guide covers how to test.

The most important parameter is nitrate, and dissolved organics in general. Discus are sensitive to accumulated waste, which is why serious keepers do large, frequent water changes with aged or conditioned water matched for temperature.

06

Diet and feeding

Wild discus graze on insect larvae, small crustaceans, worms and some plant matter. In captivity, a quality discus granule or pellet (for example Hikari Discus Bio-Gold, Tetra or Sera discus foods) makes a good staple. Add frozen bloodworms, brine shrimp and mysis several times a week. Homemade beef heart mixes are a traditional discus food that many breeders still use, but they foul water quickly, so use them sparingly in display tanks.

Feed adults 2–3 small meals a day, and juveniles 4–6 times a day to support growth. Remove leftovers after a few minutes. Discus are slow, deliberate eaters, so fast and greedy tank mates can leave them hungry; our guide on how often to feed aquarium fish has more on portioning.

07

Behavior and discus tank mates

Discus are peaceful, social fish that live in a pecking order. Some chasing at feeding time is normal; a fish that hides in a corner, darkens and stops eating is a warning sign. Sudden movement, loud tanks and bright, bare setups make them nervous, so give them cover and a calm spot in the room.

Tank mates must tolerate high temperatures, stay peaceful and not compete aggressively for food. The classic choices are a large school of cardinal tetras or rummy nose tetras, heat-tolerant corydoras such as Corydoras sterbai, and a bristlenose pleco. Our guide to discus tank mates goes through every option.

• Usually compatible: cardinal tetras, rummy nose tetras, Corydoras sterbai, bristlenose pleco, hatchetfish
• Risky: German blue rams and Apistogramma (need space and caves), angelfish (often discouraged for disease and competition)
• Avoid: fin nippers such as tiger barbs, boisterous fish, Chinese algae eaters, any species that needs cooler water

08

Breeding discus

Discus form pairs within a group. A pair cleans a vertical surface (often a breeding cone) and lays 100–400 eggs. Both parents fan the eggs, which hatch in about 2–3 days at breeding temperatures, and the fry become free-swimming a few days later.

What makes discus unique is parental feeding: for the first one to two weeks, the fry eat a protective mucus produced on the parents' skin. Breeders usually add baby brine shrimp after about a week. Successful breeding generally needs very soft, acidic water, a dedicated bare tank and excellent hygiene. It is a project for experienced keepers, not a beginner side effect.

09

Common discus diseases

Most discus illnesses are linked to stress, poor water quality or new fish introduced without quarantine. Quarantine every newcomer for 4–6 weeks and acclimate slowly. For any serious case, especially several sick fish at once, consult an aquatic veterinarian.

10

Recommended gear

Reliable heating is essential. A 75-gallon discus tank usually needs 250–300 W of heating, ideally split between two heaters so one failure does not crash the temperature; see our best aquarium heater picks and the guide to fish tank temperature. For filtration, a canister filter or large sponge filters with gentle return flow work well; compare models in our best canister filter guide.

Add a liquid test kit, a good gravel vacuum or siphon for frequent water changes, and a water conditioner. A TDS meter and a reverse osmosis unit become useful if your tap water is hard or if you plan to breed.