What You Should Know Before Adding a Cardinal Tetra to Your Aquarium

Thinking about adding Cardinal Tetras to your tank? These little beauties are a favorite for a reason — they’re peaceful, colorful, and pretty easy to care for once you get the hang of things. We've worked with tetras quite a bit over the years, and while they’re not completely effortless, they’re definitely beginner-friendly — especially if you’re not trying to breed them.

Here’s what you really need to know before bringing Cardinal Tetras home:

Cardinal Tetras 101: What Makes Them Great

Cardinal Tetras (Paracheirodon axelrodi), sometimes called Red Neon Tetras, are small freshwater fish known for their vibrant red and blue stripes. They top out at about 2 inches long and live around 4 years in a healthy tank.

They’re social fish that love to school, so you’ll want to keep at least six together. Honestly, the more the better — as long as your tank can handle it. A 10-gallon tank is the bare minimum, but if you can go bigger, do it. Overcrowding leads to stress and illness, so don’t push your luck with the “3 per gallon” rule some people throw around.

Easy to Keep, Not So Easy to Breed

Cardinals are low-maintenance when it comes to day-to-day care. They’ll thrive in stable water conditions, eat a mix of high-quality flakes and frozen or live food, and don’t need fancy upgrades in their tank.

However, breeding them is a whole different story. It requires a separate tank with exact conditions — soft, acidic water, dim lighting, and a lot of patience. Even if you get them to spawn (usually at night), raising the fry is tricky. We don’t recommend trying this until you’ve gotten really comfortable with your tank setup and fishkeeping basics.

Tankmates That Work (and Ones That Don’t)

Cardinal Tetras are peaceful and play well with others — as long as those others aren’t big enough to eat them. Good companions include:

• Other small tetras (like Neons)
• Corydoras
• Rasboras
• Dwarf Gouramis
• Cherry shrimp
• Kuhli loaches

Avoid aggressive or much larger fish who might see them as snacks.

And yes, they can live with Angelfish… but only if the Angelfish are raised with them and aren’t large enough to view Cardinals as prey. Always keep an eye on behavior if you’re mixing species.

Feeding and Care Tips

These fish are omnivores, so they’re not picky — but they do best on a diet that’s mostly high-quality flakes with the occasional treat of frozen or live food (like brine shrimp or daphnia). They should be fed 2–4 times a day in small amounts they can finish in a few minutes.

One thing we’ve learned the hard way: overfeeding can mess up your water quality fast. Always err on the side of underfeeding and clean up uneaten food quickly.

Water Conditions They Need

Coming from the Amazon, Cardinal Tetras are used to soft, acidic water. Here’s the sweet spot for them:

• Temperature: 73–81°F (23–27°C)
• pH: 4.5–6.2
• Hardness: Under 4 dGH (very soft)

If your tap water is hard or alkaline, consider using peat filtration or reverse osmosis water to bring the levels down. Stability is key — sudden changes can be deadly.

Common Issues to Watch Out For

If your Cardinals are dying off, the most common causes are:

• Poor or inconsistent water quality
• Overcrowding
• Overfeeding
• Stress from aggressive tankmates
• Disease (look for color loss, curved spines, or erratic swimming)

A good habit is to test your water weekly and do regular partial water changes — it makes a bigger difference than you might think.

A Note on Conservation

Cardinal Tetras aren’t endangered, but they come from sensitive ecosystems in the Amazon. Wild habitats are at risk due to deforestation and fires, so if you want to be mindful, look for captive-bred fish whenever possible. It supports sustainable practices and reduces pressure on wild populations.

Final Thoughts

If you’re just starting out or looking to add a splash of color to your tank, Cardinal Tetras are a solid choice. They’re peaceful, beautiful, and surprisingly hardy — as long as you give them stable water conditions and a proper group to school with.

They may not be the easiest fish to breed, but for everyday aquarium life? They’re a joy to keep. Just be prepared to feed them regularly and keep an eye on your water quality, and you’ll have a happy, shimmering school in no time.