Introduction

The discus is a schooling fish that should never be kept alone.
One of the most common questions among aquarists is:

👉 How many discus can you keep in an aquarium?

The answer depends on several factors: tank size, filtration, water changes, and fish size.

In this complete guide, you will learn:

• the ideal number of discus based on tank size
• common mistakes to avoid
• how to optimize stocking
• breeder tips for successful discus keeping

Discus Are Schooling Fish

Discus naturally live in groups.
In an aquarium, this behavior must be respected.

👉 Minimum recommended: 5 to 6 discus

Why?

• reduced aggression
• more stable hierarchy
• lower stress levels
• natural behavior

⚠️ Keeping only 2 or 3 discus often leads to:

• excessive dominance
• chronic stress
• weakened fish

How Many Discus per Tank Size?

Here is a reliable starting point:

👉 These values apply to adult discus (12–15 cm).

Adjust Based on Filtration and Maintenance

Tank size is not the only factor.

Two identical tanks can support different stocking levels depending on:

1. Filtration

• minimum 5x tank volume per hour
• ideally clean, well-oxygenated water

2. Water Changes

• at least 20–30% per week
• more frequent changes = higher stocking possible

3. Bioload

• feeding intensity
• presence of other fish

👉 The better your maintenance routine, the more discus you can safely keep.

Special Case: Juvenile Discus

Young discus (5–10 cm) can be kept at higher density.

👉 Why?

• rapid growth
• higher feeding needs
• less territorial behavior

Example:

• 300 L → 8 to 10 juvenile discus possible

⚠️ But:

• frequent water changes required
• multiple feedings per day

Common Mistakes to Avoid

❌ Too few discus

→ stress and dominance issues

❌ Tank too small

→ stunted growth and conflicts

❌ Poor water quality

→ disease and color loss

❌ Mixing sizes

→ smaller fish get outcompeted

Can You Keep Other Fish with Discus?

Yes, but carefully.

Compatible species:

• Cardinal tetras
• Corydoras
• Ancistrus

⚠️ Watch out for:

• food competition
• increased bioload

LB Discus Breeder Tip

👉 It is always better to keep fewer fish in excellent conditions than too many in a borderline setup.

In my breeding setup, the key is simple:

• clean water
• stability
• proper feeding
• daily observation

This is how you get:

• round discus
• vibrant colors
• optimal growth

Conclusion

The number of discus depends on tank size, but above all on maintenance quality.

👉 Simple rule:

• minimum 5 to 6 discus
• at least 300 L to start
• more volume = more stability

Following these basics helps avoid most common problems.

Article written by Franck Le Bozec – Discus Breeder in Brittany

Founder of LB Discus, a breeding facility specialized in French-bred discus reproduction.