Discus / King of the aquarium (Symphysodon aequifasciatus) care guide

Quick facts

Adult size: 20 cm
Lifespan: can live up to 15 years
Tank zone: mid
Temperament: peaceful
Difficulty: advanced

Water parameters

Temperature: 28–32°C
pH: 5.5 to 7.0
Hardness: 1 to 8 dGH

Tank requirements

Minimum volume: 300 L
Minimum length: 120 cm
Flow: low
Lighting: dim preferred
Substrate: any
Driftwood: preferred
Hiding spots: needed
Open swimming room: needed

Feeding

Diet: omnivore, feeds primarily at the mid.

Discus-specific pellets, frozen bloodworms, beef heart mix (controversial but widely used). Picky eaters; new fish often refuse food for days. Multiple small feedings per day work better than one large one.

Compatibility

The most demanding common freshwater fish. Temperature requirement (28–32°C) limits compatible tankmates to species that tolerate sustained heat: cardinal tetras, rummy-nose tetras, corydoras sterbai, bristlenose plecos
Keep in groups of 5+. Discus establish a hierarchy; fewer than 5 means the bottom fish gets bullied relentlessly
Water quality must be pristine. Large water changes (50%+) multiple times per week is standard practice for serious discus keepers. Bare-bottom tanks are common because they're easier to keep clean
Discus fry feed on a mucus coating the parents secrete from their skin. This is why breeding discus is a different hobby from keeping discus
Modern captive-bred strains (pigeon blood, marlboro red, blue diamond) are more forgiving than wild-caught; wild discus are expert-only

Habitat

Native to the Amazon basin in Brazil, Peru, and Colombia. Found in slow blackwater tributaries with fallen trees and submerged root tangles. Three species are recognized: S. aequifasciatus (green/brown), S. discus (Heckel), and S. tarzoo (sometimes lumped with aequifasciatus). The aquarium trade has produced dozens of line-bred color strains that don't resemble any wild fish.

Breeding

Pair-forming substrate spawner. A bonded pair cleans a vertical surface and lays 100-300 eggs. Both parents guard and fan the eggs. Unique among aquarium fish: fry feed on a mucus secretion produced on the parents' skin for the first 1-2 weeks (called "discus milk"). This parental feeding is essential; fry raised without parents have much lower survival rates. Breeding requires extremely clean, soft, acidic water (pH 5.5-6.5, TDS below 100), high temperature (28–30°C), and a stress-free environment. Discus breeding is a serious commitment.

Common problems

Discus are demanding fish. They require warm water (28–30°C), pristine water quality, and frequent water changes (many serious keepers do 50% daily). Internal parasites (hexamita, intestinal worms) are extremely common, especially in imported fish. Deworming with praziquantel and treating with metronidazole is standard practice for new discus. Stress shows immediately as darkened body color, clamped fins, and hiding. They are not community fish in the usual sense; tankmates must tolerate high temperatures and not outcompete discus for food.

Bioload

Bioload coefficient: 6.0 (large cichlid kept at high temperatures which accelerates metabolism and waste production).

Bioload coefficients are calibrated against the neon tetra as the anchor (1.0). See the methodology page for the formula and how each value was derived.