If you’ve ever stood in front of your aquarium, watching those adorable little Corydoras dart and sift through the gravel, you’ve probably wondered — how many Corydoras in a 20 gallon?
It’s a question almost every fish keeper asks at some point, and for good reason.
Corydoras are social, playful, and thrive best in groups — but getting the right number is key to keeping them happy and healthy.
In this article, you’ll discover how many Corydoras you can safely keep in a 20-gallon tank, what factors affect their comfort and space needs, and how to create the perfect environment for them to flourish.
Whether you’re new to fishkeeping or a seasoned aquarist, you’re in the right place. Let’s dive in and find out!
🐠 What Are Corydoras?
Before diving into numbers, let’s get to know these charming little fish.
- Corydoras, often called Cory catfish, are small freshwater fish native to South America.
- They belong to the Callichthyidae family and are known for their gentle nature and armored bodies.
- Most Corydoras species grow to about 2 to 3 inches long.
- They thrive in groups and love to scavenge leftover food at the tank’s bottom.
These playful fish are often compared to the “clean-up crew” of your aquarium — always busy and endlessly entertaining!
📏 Direct Answer | How Many Corydoras in a 20 Gallon Tank?
The ideal number of Corydoras for a 20-gallon tank is 6 to 8 small-sized Corydoras, such as Panda, Pygmy, or Salt and Pepper Corys.
If you choose larger species like Bronze or Emerald Corys, limit it to 4 to 5 to maintain water quality and comfort.
Quick Rule of Thumb:
➡️ 1 inch of fish per gallon of water (but always account for activity level and tank mates).
📊 Recommended Stocking Chart
| Corydoras Type | Average Size | Ideal Number (20 Gallon) | Notes |
| Pygmy Corydoras | 1 inch | 8–10 | Very small, best for nano setups |
| Panda Corydoras | 2 inches | 6–8 | Active and social |
| Bronze Corydoras | 2.5 inches | 4–5 | Larger, need more space |
| Sterbai Corydoras | 2.5 inches | 4–5 | Prefer warmer temps |
| Julii Corydoras | 2 inches | 6–7 | Peaceful and adaptable |
🌿 Why Tank Size and Fish Count Matter
Overstocking is one of the most common beginner mistakes. Here’s why balance is key:
- Water Quality: More fish means more waste, which can quickly spike ammonia and nitrate levels.
- Oxygen Levels: Corys are bottom dwellers — too many can lead to oxygen competition.
- Behavior: They’re social but need personal space to swim and forage.
- Health: Crowded tanks stress fish, making them more prone to disease.
A properly stocked 20-gallon tank keeps your Corys active, healthy, and playful.
💡 How to Remember the Ideal Stock Ratio
A fun trick:
“20 gallons, 20 fins.”
Most Corydoras have a small dorsal fin and tail fin — 6 to 8 fish give you about 20 little fins swimming around! Easy, right?
Or simply think:
➡️ 1 Cory per 2–3 gallons of tank water.
⚠️ Common Mistakes to Avoid
Even experienced aquarists make these errors — but you don’t have to!
- ❌ Mixing large and tiny species in small tanks
- ❌ Skipping the group rule (Corys must be in groups of at least 5+)
- ❌ Ignoring filtration strength — Corys need clean, well-oxygenated water
- ❌ Using rough gravel — always go for smooth sand substrate to protect their barbels
- ❌ Forgetting tank mates — don’t add aggressive or fin-nipping fish
⚖️ Are All Corydoras the Same Size?
Nope! That’s where many people get confused.
- Pygmy Corys are tiny — barely an inch.
- Bronze and Emerald Corys can grow over 3 inches.
This size difference means you must adjust the count based on species. Smaller Corys = more per gallon. Larger Corys = fewer per gallon.
🌍 Real Life Examples
- Example 1: You have a 20-gallon community tank with guppies and tetras. → Go for 5 small Corys to maintain balance.
- Example 2: A 20-gallon tank dedicated only to Pygmy Corys. → You can safely keep up to 10.
- Example 3: A planted tank with caves and hiding spots. → 6 to 8 medium-sized Corys will thrive beautifully.
❓ FAQ | How Many Corydoras in a 20 Gallon?
Q1: Can I keep just two Corydoras in my 20-gallon tank?
A: It’s not recommended. Corydoras are schooling fish and feel stressed when kept in pairs. Aim for at least 5–6.
Q2: What’s the best Corydoras species for a 20-gallon tank?
A: Panda, Pygmy, or Julii Corydoras are perfect — small, peaceful, and very social.
Q3: Can I mix different types of Corydoras?
A: Yes, but keep at least 4–5 of each type so they can shoal comfortably.
Q4: Do Corydoras need a heater?
A: Most species prefer temperatures between 72–78°F (22–26°C). A heater helps keep it consistent.
Q5: Can I keep Corydoras with shrimp or snails?
A: Absolutely! They’re peaceful and won’t harm shrimp or snails.
Q6: How often should I clean a 20-gallon Corydoras tank?
A: Perform 20–25% water changes weekly and vacuum the substrate gently.
🐡 Conclusion
A 20-gallon tank is a wonderful home for a small school of Corydoras — just make sure you balance size, species, and filtration. With 6 to 8 small Corys, smooth sand, and clean water, you’ll enjoy a lively, happy, and thriving little aquarium community.
Jordan Foster is a modern American author whose stories blend heartfelt emotion with fresh imagination. Known for his simple yet powerful writing style, he explores themes of love, hope, and resilience in ways that touch readers deeply.
His works include Ashes and Aurora, The Last Ember, and Beneath the Quiet Stars—each offering a unique journey that stays with readers long after the final page.