Discus are large, disc-shaped cichlids from the slow, warm, soft blackwaters of the Amazon, and are among the most demanding aquarium fish.
Their calm appearance hides exacting requirements that frustrate beginners.
Reaching 15-20cm across and living over a decade, they need clean warm water, careful diet and the company of their own kind.
Discus reward dedicated keepers with strong colour but decline quickly under neglect, which places them firmly in advanced territory.
Housing
Discus need a tall, deep, fully matured tank of at least 250L for a group, kept very warm at 28-30C, soft and acidic (pH 6.0-7.0) with low nitrate.
They are intolerant of pollution and unstable parameters.
Use gentle filtration, subdued lighting, driftwood and tall plants to mimic flooded forest.
Frequent large water changes, often several times weekly, are needed to keep nitrate minimal.
Quarantine and stability are critical; even small swings in temperature or chemistry cause stress and disease.
Diet
Discus are protein-hungry omnivores fed a varied menu of frozen bloodworm, brine shrimp, specialised discus pellets and traditional beefheart-based mixes.
Young, growing fish need feeding several times daily, which adds to the water-change burden.
Varied, quality feeding supports colour and growth, but heavy protein loads the water, so feeding and water management go hand in hand.
Avoid overfeeding and remove uneaten food promptly.
Feed measured portions to keep the warm, sensitive water clean.
Health
Discus are delicate and stress-prone, vulnerable to discus plague, hexamita and hole-in-the-head, gill flukes and bacterial infections, almost always linked to water quality or imported-stock disease.
Darkening colour, clamped fins and stringy white faeces signal trouble.
Strict quarantine of new fish, clean warm water and a low-stress group setting prevent most problems.
Sudden hiding, refusal to eat and rapid breathing call for immediate investigation.
Sourcing captive-bred fish from reputable breeders substantially reduces disease risk.
Temperament
Discus are peaceful, shy and intensely social, and suffer if kept alone or in too small a group; six or more lets them form a stable hierarchy and feel secure.
Lone or paired discus often become withdrawn and stressed.
Keep them only with calm, warm-water tankmates such as cardinal tetras and corydoras that tolerate high temperatures, avoiding boisterous or nippy fish.
Their timid nature means they are easily outcompeted at feeding time, so choose companions with care.
A good fit for
Experienced aquarists seeking a challenge
Keepers able to do frequent large water changes
Those wanting a striking centrepiece group
Hobbyists who source captive-bred stock
Common mistakes to avoid
Keeping too few, causing chronic stress
Unstable or cool water below 28C
Skipping quarantine and importing disease
Boisterous tankmates outcompeting timid discus
Is your enclosure big enough?
Minimum volume250 litres (66 US gallons)
CompanyCannot be kept alone. The minimum is 5, and the space above is for that group.
In a fish tank the patient is usually the water. Test before you treat — dosing a healthy tank for a disease it does not have makes things worse.
Go now
Any detectable ammonia or nitrite in a stocked tankLarge water change now with dechlorinated, temperature-matched water. Stop feeding. Test again in 12 hours. Both are directly toxic. How toxic the ammonia reading is depends on pH and temperature, so the same number can be harmless or lethal.
Now
Fish gasping at the surface, or crowding the filter outflowIncrease surface agitation immediately, then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems.
Now
Sudden deaths, more than one fish in a dayTest ammonia, nitrite, nitrate and temperature before doing anything else. Do not add medication yet. Multiple simultaneous deaths point at the water or the equipment, not at a pathogen.
Now
Today
Flashing — repeatedly scraping against decor or substrateTest the water, then look closely for parasites. Irritation is either chemical or parasitic; the test tells you which before you medicate.
Today
White salt-grain spots over the body and finsBegin the appropriate treatment today and check the temperature. The parasite's life cycle is temperature-driven, and it multiplies with every cycle you wait.
Today
Soon
Clamped fins, hiding, or refusing food for more than two daysTest the water and review recent changes. Usually the earliest visible sign of a parameter drifting.
A few days
Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.
This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.
What it really costs
Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.
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