What Size Tank Do Discus Need?
Short answer: Discus need at least a 55-gallon tank for a group of 5-6. The median discus tank in our 315-tank dataset is 75 gallons, with most keepers running 55-110 gallons.
Discus at a glance
- Scientific name
- Symphysodon aequifasciatus
- Adult size
- ~5.5″
- Temperature
- 82–86°F
- pH
- 5–7.5
- Minimum tank
- 55 gal
- Temperament
- semi aggressive
- Social
- schooling — keep 5+
- Reference
- Wikipedia
Discus need at least a 55-gallon tank. The median discus keeper in our 315-tank dataset (July 2026 snapshot) runs a 75-gallon tank, and 97% use tanks of 10 gallons or larger. Discus (Symphysodon aequifasciatus) are large, round cichlids that reach 5.5 inches and must be kept in groups of at least 5-6, which rules out anything under 55 gallons for a healthy setup.1
What real keepers actually use
We pulled every discus setup from the AquaGauge dataset where the keeper reported tank size. That gave us 315 tanks from r/discus.
| Stat | Value |
|---|---|
| Median tank size | 75 gal |
| Mean tank size | 86.7 gal |
| 25th percentile (Q1) | 55 gal |
| 75th percentile (Q3) | 110 gal |
| Range | 3-500 gal |
| Tanks of 10 gal or more | 97% |
The middle half of discus keepers use tanks between 55 and 110 gallons. The 75-gallon sweet spot makes sense: it gives a group of 5-6 adults enough horizontal and vertical space, handles the bioload, and is still common enough to find affordable equipment for.
Why discus need big tanks
Three factors drive the minimum up:
Group fish. Discus are social cichlids that form loose hierarchies. Keeping fewer than 5 concentrates aggression on subordinate fish, leading to stress, darkened colors, and refusal to eat. A 55-gallon fits 5 adults; a 75-gallon fits 6-8 comfortably.
High bioload. Each adult discus carries 8.0 bioload units in the stocking calculator. Five discus alone account for 40 units, leaving little room for tankmates in a 55-gallon. A 75-gallon (75 units) gives breathing room for a school of cardinal tetras or corydoras.
Warm water = less oxygen. Discus run hot: the median keeper temperature in our dataset is 84 F (Q1 83, Q3 86). Water at 84 F holds less dissolved oxygen than a typical community tank at 76 F. A larger water volume and strong filtration compensate for that.
Tank size by group size
Here is what each common tank size handles, using the 8.0 bioload-per-discus figure:
- 55 gallon: 55 units total. Fits 5 discus (40 units) with a small cleanup crew. Tight but workable for adults.
- 75 gallon: 75 units. Fits 6-8 discus (48-64 units) with a school of dither fish. The median size in our data.
- 125 gallon: 125 units. Fits 10-12 discus with multiple tankmate schools. For serious hobbyists and breeders.
Use the stocking calculator to model your exact combination before buying.
Water parameters in real discus tanks
Discus keepers run warmer and softer water than most freshwater community tanks. See the full discus water parameters breakdown for temperature, pH, and nitrogen data. From our dataset:
| Parameter | Median | Q1-Q3 range |
|---|---|---|
| Temperature | 84 F | 83-86 F |
| pH | 7.0 | 6.5-7.6 |
FishBase lists the species’ natural range as 26-30 C (79-86 F) and pH 5.0-8.0.1 Real keepers cluster at the warm end. The ideal pH guide covers how to read and adjust pH for sensitive species like discus.
Tankmate considerations
Discus are not aggressive predators like angelfish, but their high temperature requirement limits compatible tankmates. Most community fish prefer 74-78 F and will stress at 84 F. Safe options include cardinal tetras, rummy-nose tetras, corydoras (some species tolerate warmer water), and ram cichlids.2
Seriously Fish notes that discus are “very shy, skittish fish” that need substantial cover to feel secure.2 Heavily planted setups with tall Amazon swords and driftwood reduce stress and bring out brighter colors.
How we counted
We analyzed 315 discus setups from the AquaGauge dataset of freshwater community tanks compiled from public Reddit fishkeeping posts (r/discus). Keepers self-reported tank size. Temperature and pH data come from a smaller subset (n=27 for temp, n=43 for pH) where keepers reported parameters. Full methodology at /methodology/. Figures are from the July 2026 snapshot (6,414 tanks total).
Example setups from the dataset: 280-gallon community, 125-gallon planted.
Check your exact stocking
Add your fish below to see stocking %, filtration load and compatibility for your setup — live.
Planning a Discus tank. We start with your discus and filter the list to compatible tankmates — untick to see every species (incompatible ones get flagged).
Stocking — under 85% comfortable · 85–100% full · over 100% overstocked
Show the math
Gear for this setup
As an Amazon Associate AquaGauge earns from qualifying purchases. Some links below are affiliate links, at no extra cost to you. Current price and availability are shown on Amazon. Disclosure.
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HITOP 300W Adjustable Aquarium Heater Holds 82-86 F in a 55-75 gallon tank, the warm range discus need year-round. Check price on Amazon → -
Fluval 407 Performance Canister Filter Rated for up to 100 gallons with gentle flow that suits tall discus tanks. Check price on Amazon → -
Seachem Prime Water Conditioner (500 ml) Detoxifies chlorine and ammonia during the frequent water changes discus tanks require. Check price on Amazon → -
API Freshwater Master Test Kit Liquid tests for ammonia, nitrite, and nitrate confirm the tank is cycled before adding discus. Check price on Amazon →
FAQ
- Can discus live in a 40-gallon tank?
- A 40-gallon is too small for discus kept properly. Discus are group fish that need at least 5-6 together, and each carries 8.0 bioload units. A 40-gallon tank cannot handle that load. In our 315-tank dataset the 25th-percentile discus tank is 55 gallons, so a 40-gallon sits in the bottom quarter of real setups.
- Is a 75-gallon tank good for discus?
- A 75-gallon is the median discus tank size in our dataset. It fits 5-6 adult discus (40-48 bioload units) with room for a small school of dither fish like cardinal tetras or corydoras.
- How many discus can I keep in a 55-gallon?
- About 5-6. A 55-gallon handles roughly 55 bioload units, and each discus adds 8.0. That gives you room for 5-6 discus with minimal tankmates. Keep at least 5 to spread aggression.
- Do discus need a tall tank?
- Yes. Adult discus reach 5-6 inches in diameter and need vertical swimming space. A standard 75-gallon (21 inches tall) or 55-gallon (21 inches tall) works. Avoid long, shallow tanks like 40-gallon breeders (16 inches tall).
Sources
- Symphysodon aequifasciatus summary, FishBase. View source ↗
- Symphysodon aequifasciatus, Seriously Fish. View source ↗
Freshwater aquarist of 8+ years.