Discus — Tank Size, Adult Size, Lifespan & Full Care Guide
Symphysodon aequifasciatus
Care requirements at a glance
| Scientific name | Symphysodon aequifasciatus |
|---|---|
| Group | Cichlid |
| Adult size | 8 in (20.3 cm) |
| Minimum tank | 55 gallons |
| Temperature | 82-88°F |
| pH | 5.5-7 |
| Hardness | 1-8 dGH |
| Temperament | Peaceful |
| Social | Group (5+) |
| Diet | Carnivore |
| Swim level | Mid |
| Care level | Hard |
| Lifespan | ~10 years |
How big do Discus get? Adult size explained
Discus are a large species and the single most common stocking mistake in this hobby is underestimating that. The fish sold at 2 inches in a cup will not stay that size. Adult discus reach 8.0 inches (20.3 cm). Fish you buy are almost always juveniles at roughly 3.6″, so plan the tank around the adult number, never the size in the bag.
| Stage | Typical length |
|---|---|
| Size sold in stores | about 3.6″ (9.1 cm) |
| Half-grown | 6.0″ (15.2 cm) at roughly 12 months |
| Full adult size | 8.0″ (20.3 cm) by 24 months |
| Sexual maturity | usually before full size, around 10–12 months |
Growth rate depends mostly on feeding quality and water changes in the first six months. Stunted growth from poor water does not make the fish 'stay small' safely — internal organs keep growing, which shortens lifespan considerably.
Discus tank size: minimum vs recommended
The 55-gallon figure is a floor, not a target. It assumes a cycled, filtered, planted tank and an owner who does weekly water changes.
Remember that the minimum tank and the minimum group interact. Discus need at least 5 individuals, so the real question is not “will one fit in 55 gallons” but “will 5 of them fit”. That is why we recommend 110 gallons as the practical starting point.
| Tank size | Discus it supports | Verdict |
|---|---|---|
| 5 gallons | — | Too small |
| 10 gallons | — | Too small |
| 20 gallons | — | Too small |
| 29 gallons | — | Too small |
| 40 gallons | — | Too small |
| 55 gallons | 6 in one group | Workable minimum |
| 75 gallons | 8 in one group | Workable minimum |
Numbers assume discus are the main occupants with light additional stocking, a filter rated for the tank, and weekly 25–30% water changes. Use the stocking calculator to model a mixed community.
Discus group size: how many should you keep together?
Discus are a shoaling species. In groups below 5 they show measurable stress behaviour: faded colour, hiding, refusing food and darting at the glass. This is not a preference — it is how the species regulates its own sense of safety.
Minimum: 5. Better: 7–10. Colour and natural behaviour improve noticeably once the group passes about 9. If your budget forces a choice between more species and bigger groups, always choose bigger groups — a tank with two well-sized shoals looks far better than one with six lonely singletons.
Discus water parameters
| Parameter | Range | Notes |
|---|---|---|
| Temperature | 82–88°F (28–31°C) | aim for 85°F and keep it stable |
| pH | 5.5–7 | target 6.2; stability beats the exact number |
| Hardness (GH) | 1–8 dGH | soft to moderate |
| Ammonia (NH₃) | 0 ppm | any reading means the tank is not cycled |
| Nitrite (NO₂) | 0 ppm | any reading is an emergency — water change now |
| Nitrate (NO₃) | under 20–40 ppm | controlled by water changes and live plants |
This is a soft-water species. If your tap runs above about 12 dGH you will do better with a different fish than with constant chemical adjustment — chasing parameters causes more deaths than the wrong parameters do.
Stability matters more than perfection. A tank sitting steadily at pH 7.2 is healthier than one swinging between 5.5 and 7 every week. Test your tap water first, then choose fish that match it, rather than buying the fish and fighting the water afterwards.
Ideal discus tank setup
Need warm (82-88°F), soft, acidic water and a spacious tank (55+ gallon). Keep in a group of 5+. Minimal decoration for easy cleaning. Frequent water changes are essential. Best for experienced aquarists.
| Substrate | Dark substrate brings out colour; the choice is otherwise up to you. |
|---|---|
| Planting | Plant the back and sides, leave open swimming space down the middle. |
| Flow | Moderate flow suits this species well. |
| Lighting | Moderate. Floating plants diffuse the light and make shy fish bolder. |
| Lid | Recommended — it also reduces evaporation and heat loss. |
What do Discus eat? Diet and feeding
Require a high-protein diet — beefheart mix, frozen bloodworms, brine shrimp, and quality discus pellets. Feed 2-3 times daily in small amounts. They are sensitive to water quality.
The single most common feeding error is quantity, not quality. Discus have a stomach roughly the size of their eye. Feed what disappears in about two minutes, once a day, and the tank stays clean.
Staple: meaty micro-pellet or frozen food.
- Frozen bloodworm or daphnia 2–3× per week
- Live brine shrimp as a conditioning food
- Freeze-dried tubifex sparingly
| Frequency | What to do |
|---|---|
| Daily | One small feeding of meaty micro-pellet or frozen food. Everything eaten within 2 minutes. |
| 2–3× weekly | Rotate in a second food type for variety and micronutrients. |
| Weekly | One fasting day gives the gut time to clear. Skip this for fry and for shrimp. |
Discus behaviour and temperament
Discus are peaceful and will not start trouble. Their weakness is the opposite — they are easily bullied or outcompeted for food by faster or bolder species. They spend most of their time in the middle of the tank.
Signs of a settled, healthy specimen: strong colour, fins held open, active foraging, and a normal reaction to your hand near the glass. Signs of a stressed one: clamped fins, faded colour, hovering in a corner, gasping at the surface, or hiding constantly during daylight hours.
How long do Discus live?
| Factor | Effect on lifespan |
|---|---|
| Stable, cycled water | Adds years. The most common cause of early death in discus is ammonia exposure in an uncycled tank. |
| Correct temperature | Running warmer than 88°F speeds metabolism and shortens life; running cold invites disease. |
| Varied diet | Single-food diets cause organ problems and colour loss over time. |
| Right group size | Chronic stress from wrong social setup measurably shortens lifespan. |
| Genetics | Mass-bred stock from large farms often lives noticeably shorter than quality or local stock. |
Discus tank mates: what works and what does not
Compatibility is decided by four things, in this order: water parameters (82–88°F, pH 5.5–7), adult size, temperament, and swimming level. A fish that matches on three and fails on one is not a match.
Good tank mates
Avoid these
Check any pairing in the compatibility tool →
Breeding discus
Pair-forming cichlids that lay eggs on vertical surfaces. Both parents produce "discus milk" (mucus) for the first week of fry. Pairs are devoted but can be picky about conditions.
If you want fry to survive, the practical route is a separate, gently filtered grow-out tank. In a community tank almost every egg or fry becomes food, which is normal and not a sign that anything is wrong.
Male vs female discus
Difficult to sex. Males are slightly larger with a pointed breeding tube. Females have a blunt tube. Pairs form naturally from a group — buy 5-6 juveniles and raise them together.
Discus health, diseases and prevention
| Problem | What you see | What to do |
|---|---|---|
| Ich (white spot) | Salt-grain white dots, flicking against decor | Raise temperature slowly to 82°F and treat; aquarium salt is usually tolerated. |
| Fin rot | Ragged, receding or blackened fin edges | Almost always water quality. Increase water changes before reaching for medication. |
| Bloat / constipation | Swollen belly, stringy white waste | Fast 2–3 days, then feed blanched deshelled pea or daphnia. |
| Bacterial infection | Red streaks, ulcers, lethargy | Quarantine and treat with a broad-spectrum antibacterial; review water quality. |
| Stress / chronic hiding | Faded colour, clamped fins | Check parameters, group size and tank mates before medicating. |
Prevention beats treatment every time: quarantine new arrivals for two weeks, keep the tank understocked rather than at maximum capacity, and do a consistent weekly water change instead of a large emergency one every month.
First 30 days with Discus: a practical checklist
Most losses happen in the first month, and almost all of them are avoidable. This is the schedule we recommend.
| Before you buy | Do not add fish yet. The tank must be fully cycled: ammonia 0, nitrite 0, nitrate present. A cycled tank is the single biggest predictor of whether these animals survive. |
|---|---|
| Day 1 — acclimation | Float the bag 20 minutes to match temperature, then drip acclimate over 45–60 minutes. Never pour store water into your tank. |
| Days 1–3 | Lights off or dimmed. Do not feed on day one. Expect hiding and pale colour; this is normal. |
| Days 4–14 | Test ammonia and nitrite every second day — new stock is the classic trigger of a mini-cycle. Feed lightly. Watch that every individual is eating. |
| Days 14–30 | Colour should be full and behaviour settled. This is the window where ich typically shows up — check body condition from above, not just from the side. |
| After day 30 | Now you can add the next species. Adding stock in stages rather than all at once is what keeps the filter ahead of the bioload. |
Common mistakes when keeping Discus
- Buying 2 instead of 5 — The most common mistake with this species. An under-sized group is a permanently stressed group, and stress is what makes fish susceptible to everything else.
- Buying juveniles for a small tank — Store specimens are a fraction of the 8.0″ adult size. The tank does not grow with them.
- Adding stock to an uncycled tank — Ammonia burns gills permanently. Cycle first, always — see our tank cycling guide.
- Overfeeding — Uneaten food becomes ammonia. Two minutes, once a day is the rule.
- Chasing pH with chemicals — pH adjusters cause swings that are far more dangerous than a stable pH slightly outside 5.5–7.
- Skipping quarantine — Two weeks in a separate tank prevents most disease outbreaks in an established display tank.
What does a discus setup cost?
| Item | Typical cost |
|---|---|
| Aquarium, 110 gal | $262 |
| Filter | $45 |
| Heater | $30 |
| Light | $55 |
| Substrate & decor | $109 |
| Liquid test kit | $32 |
| 5× discus | $100 |
| Estimated total | $633 |
Indicative US retail prices for a new setup. Running cost is modest: mostly electricity for the heater and filter, plus food and a water conditioner. Buying a larger tank up front is almost always cheaper than upgrading twice.
Discus compatibility: verdict per tank mate
Each pair below is a full comparison of temperature, pH, adult size and temperament. Green means compatible, amber means workable with conditions, red means avoid.
Open the full compatibility matrix
Discus FAQ
What size tank do discus need?
The minimum tank size for discus is 55 gallons (208 litres). Because they need a group of at least 5, we recommend 110 gallons or larger for a healthy long-term setup.
How big do discus get?
Adult discus reach 8.0 inches (20.3 cm). Store specimens are usually juveniles at around 3.6 inches, so always plan the tank around the adult size.
How long do discus live?
Discus typically live about 10 years in a well-maintained aquarium. Stable water quality and a varied diet are the two biggest factors in reaching the upper end of that range.
How many discus should I keep together?
Keep at least 5 together. Groups of 7 to 10 show noticeably better colour and more natural behaviour. Below 5 they become stressed, hide and lose colour.
What water parameters do discus need?
Keep discus at 82–88°F (28–31°C), pH 5.5–7, and hardness 1–8 dGH. Ammonia and nitrite must both read zero at all times.
Are discus good for beginners?
No. Discus are rated difficult and are best attempted after a year or so of experience with stable, well-maintained tanks.
What do discus eat?
Require a high-protein diet — beefheart mix, frozen bloodworms, brine shrimp, and quality discus pellets. Feed 2-3 times daily in small amounts. They are sensitive to water quality.
Do discus need a heater?
Yes. Discus need 82–88°F, which is above typical room temperature. An adjustable heater sized to the tank is essential — temperature swings cause more disease than a slightly wrong average.
Do discus need a filter?
Yes. A filter houses the bacteria that convert ammonia to nitrate. Choose a filter rated for at least your tank volume, ideally a size up.
Can discus live alone?
They can survive alone but should not be kept that way. Discus are a shoaling species and a lone individual is a chronically stressed one, which shortens its life.
What fish can live with discus?
Good tank mates include Guppy, Platy, Swordtail, Dwarf Gourami, Pearl Gourami, Honey Gourami. Match water parameters first, then temperament, then adult size — anything that can fit them in its mouth eventually will.
What should you not keep with discus?
Avoid Neon Tetra, Cardinal Tetra, Ember Tetra, Endler's Livebearer, Bolivian Ram, Bronze Corydoras. These are either large enough to eat them, aggressive enough to harass them, or need water parameters too far outside 82–88°F and pH 5.5–7.
Are discus aggressive?
No. Discus are peaceful and will not harass other fish. The risk runs the other way — they are easily bullied or outcompeted for food.
How do you tell male from female discus?
Difficult to sex. Males are slightly larger with a pointed breeding tube. Females have a blunt tube. Pairs form naturally from a group — buy 5-6 juveniles and raise them together.
Do discus breed in a home aquarium?
Pair-forming cichlids that lay eggs on vertical surfaces. Both parents produce "discus milk" (mucus) for the first week of fry. Pairs are devoted but can be picky about conditions.
Why are my discus hiding or losing colour?
In order of likelihood: the tank is not fully cycled (test ammonia and nitrite), the group is too small, the temperature is unstable, or a tank mate is harassing them. Fading colour is the earliest visible stress signal in this species — test the water before treating for anything.
How much does a discus setup cost?
Expect roughly $628 for a complete new 110-gallon setup including tank, filter, light, substrate, a test kit and the animals themselves. Buying the right size once is cheaper than upgrading twice.