Freshwater Fish · Cichlids

Discus

Symphysodon aequifasciatus

Demanding, disc-shaped Amazon cichlidsAdvanced

Lifespan: 10-15 years
Size: 6-8 in diameter
Social needs: Strongly social; keep 6+ together
Time: High (warm water, frequent large changes)
Cost: High
Diet: Omnivore (frozen foods, discus pellets, beefheart-based mixes, some plant matter)

Overview

What is this animal?

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 6-8 in 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.

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Lone or paired discus often become withdrawn and stressed.

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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 82°F
Skipping quarantine and importing disease
Boisterous tankmates outcompeting timid discus

Enclosure

Minimum 75 gallons, for a group of 6

Cannot be kept alone. The minimum is 6, and the space above is for that group.

Discus need a tall, deep, fully matured tank of at least 75 US gallons and 4 ft long for a group of six, kept very warm at 82-86°F, 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.

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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.

Check your enclosure

Supplies

Setup

Tank and stand, 75 US gallons or more
Filter
Heater and thermometer
Substrate, plants and decor
Liquid test kit
Dechlorinator and starter supplies

Ongoing

Quality cichlid pellet sized to your species
Tropical flake as a secondary staple
Frozen bloodworm, brine shrimp and daphnia
Spirulina or vegetable flake
Live blackworms for conditioning (optional)

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Small thawing cup
Turkey baster for target-feeding shy fish
Fine net for removing leftovers

Safe substrate: Fine, smooth sand · Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras) · Bare bottom (quarantine and grow-out only)

Work out the cost

Care routine

Daily

Check temperature and equipment
Feed
Head-count and look everyone over

Every few days

Top up evaporationevery 3 days

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Weekly

Check territories and pairing
Partial water change, 25-30% weekly (discus: several changes a week)
Test the water
Wipe the front glass only

Every few weeks

Trim and thin the plantsevery 2 weeks

Monthly

Check supplies and reagent dates
Replace or recharge chemical media, if you use any (skip it in a blackwater tank)
Rinse the filter media

Health review: Quarterly water and territory review, every 3 months

Tools

Is your enclosure big enough?Check your measurements against the recommended size What will it cost?Setup, monthly and over its whole life, itemised Is this ammonia reading dangerous?Works out the toxic part from your pH and temperature

Care in depth

Diet

Omnivore (frozen foods, discus pellets, beefheart-based mixes, some plant matter)

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

Signs of good health, and the common problems

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.

Is this urgent?

6 warning signs and how fast to act, 3 of them right away

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 with fast gill movement, or crowding the filter outflowIncrease surface movement now, then test the water and check the temperature. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems, and water at discus temperatures holds less oxygen to begin with.

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 usually point at the water or the equipment rather than a pathogen, so rule those out first.

Now

Today

Clamped fins, darkening colour, hiding or refusing foodTest the water today, check the temperature, and look for white, stringy faeces. Discus decline fast once they stop eating, so sudden hiding or refusing food is a reason to investigate at once. Water quality is the usual cause, so test before you treat.

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

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.

Bedding and substrate

3 safe, 4 with a caveat, 2 to avoid

Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.

Safe

Fine, smooth sandCorrect for corydoras, kuhli loaches, eartheaters such as rams and acaras, and anything else that sifts or burrows. Barbels wear away on sharp gravel.

safe

Smooth, rounded fine gravel (not for loaches or sand-sifting cichlids; sand is better for corydoras)Rinse thoroughly before use. Grain size should be too large to swallow and too small to trap food. Kuhli loaches need sand to burrow into and rams and acaras sift mouthfuls of it; bronze and panda corydoras manage on smooth fine gravel, but sterbai corydoras need sand.

safe

Bare bottom (quarantine and grow-out only)Legitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration, and it is no long-term home for burrowing loaches or sand-sifters.

safe

With a caveat

Crushed coral or aragoniteDeliberately raises hardness and pH. Correct for rift-lake cichlids, wrong for soft-water species.

with a caveat

Aquasoil for planted tanksExcellent for plants, but most active soils soften the water and pull pH and KH down for months, and many leach ammonia for the first weeks. Right for soft-water species; wrong for hard-water animals (livebearers, rainbowfish, goldfish, and snails, whose shells erode in soft, acidic water) unless you test GH and KH and remineralise. Cycle around it; do not stock into it.

with a caveat

Very deep sand bedsAnaerobic pockets form below about 2 inches in still sand. Either keep it shallow or keep it stirred.

with a caveat

Painted or coated gravelUsually fine, but coatings chip. Test a handful in a jar for a week first.

with a caveat

Never

Sharp or angular gravel with bottom-dwellersWears down barbels and leads to infection in corydoras and loaches.

never

Anything containing metal, limestone of unknown origin, or shells in a soft-water tankSlowly alters chemistry in ways that are hard to diagnose later.

never

This is our general list for freshwater fish. We have not built one specific to Cichlids yet.

Top resources for more info

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