Patrick Farrelly · Public domain — Wikimedia Commons (cropped)

Freshwater Fish · Cichlids

Discus

Symphysodon aequifasciatus

Demanding, disc-shaped Amazon cichlidsAdvanced

Lifespan: 10-15 years
Size: 15-20cm diameter
Social needs: Strongly social; keep 5-6+ together
Time: High (warm water, frequent large changes)
Cost: High
Diet: Carnivore-leaning omnivore (frozen, beefheart, pellets)

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 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.

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Lone or paired discus often become withdrawn and stressed.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

Enclosure

Minimum 250 litres (66 US gallons) — for a group of 5

Cannot be kept alone. The minimum is 5, and the space above is for that group.

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.

Check your enclosure

Supplies

Setup

Tank and stand
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)
Small thawing cup
Turkey baster for target-feeding shy fish
Fine net for removing leftovers

Safe substrate: Inert aquarium gravel · Fine, smooth sand · Aquasoil for planted tanks

Work out the cost

Care routine

Daily

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

Weekly

Frequent partial water changeevery 3 days
Top up evaporationevery 3 days
Check territories and pairing
Clean glass and clear algae
Test the water

Monthly

Trim and thin the plantsevery 2 weeks
Check supplies and reagent dates
Rinse the filter media

Less often

Replace chemical filter media (Carbon/Purigen)every 2 months

Vet: Quarterly water and territory review — every 3 months

Top resources for more info

Independent creators and organisations we would send a friend to. We have no affiliation with any of them, and nothing here is sponsored. Links checked 2026-09-19.

YouTubers

Girl Talks FishCare how-tos by fish type, tank setup and beginner mistakes Aquarium Co-OpSpecies care guides, filtration and fish health (run by a retailer)Prime Time AquaticsSpecies profiles, stocking and water chemistry explained plainly

Sites

American Cichlid AssociationThe cichlid keepers' society, with articles and species information Seriously FishSpecies profiles with tank size, water parameters and diet for 1,800+ fish Practical FishkeepingLong-running UK fishkeeping magazine with care and species articles

Go deeper

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.

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.

Length

Width

Height

Units

Or tank volume

Units

Is this urgent?

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.

Region

How many animals

Your electricity price, per kWh

Buying the setup

Bedding and substrate

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

Safe

Inert aquarium gravelRinse thoroughly before use. Grain size should be too large to swallow and too small to trap food.

safe

Fine, smooth sandCorrect for corydoras, kuhli loaches and anything that sifts. Their barbels wear away on sharp gravel.

safe

Aquasoil for planted tanksExcellent for plants, but it leaches ammonia for the first weeks. Cycle around it; do not stock into it.

safe

Bare bottomLegitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration.

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

Very deep sand bedsAnaerobic pockets form below about 5 cm 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.

My kit says 0.25 ppm. Is that dangerous?

A liquid kit measures total ammonia, but only the un-ionised fraction is really toxic, and that fraction is governed by pH and temperature — each whole pH unit multiplies it roughly tenfold. So the same reading can be nearly harmless in one tank and lethal in another; this works out which one you are in.

Total ammonia, ppm

Temperature, C