Why Is My Neon Tetra Aggressive?

By Billy | Updated: June 27, 2022 | Neon Tetras

For my first planted aquarium, I went with neon tetras.

I bought the 5-gallon Marineland Portrait tank since it was beginner-friendly.

After a few weeks, I noticed some of my tetras acting aggressively.

Why are they acting aggressively and chasing each other?! I’m here to outline some of the common reasons I found. Hopefully, this will help you solve your aggressive Neon Tetra issue.

Quick Answer

The most common issue is getting enough Neon Tetras so they feel comfortable schooling. They’re a schooling fish, and they can act more aggressively when their numbers are under 6. Your tank might also be too small for the amount you have in there.

Here are a few common reasons why Neon Tetra acts aggressively.

1. Not Enough

Neon Tetras feel most comfortable in a school. In an ideal world, you should have a minimum of 6 together. Most chain pet stores will sell them to you without providing this information. For example, I naively went without researching Neon Tetras and got sold 5. Within the first day, one unfortunately died.

So then there were 4. This was a recipe for my Tetras to become aggressive.

2. Tank Size

Your tank size might not be big enough for them to school. I started with a 5-gallon Portrait, which wasn’t the best option for them. I should’ve got a betta fish instead and a larger one for my Neon Tetras.

3. Water Parameters

Neon Tetras are from a tropical environment, specifically the Amazon river. You must do your best to replicate the conditions of their native environment.

Ideal conditions include…

If you want to get a better idea of their native environment, check out this YouTube video. I’ve found it best to watch/read about their native environment before building your tank.

My Solution

Here’s what I did. Maybe not the solution for your situation, but still worth a share.

I bought a slightly bigger tank (UNS 60s – 10 gallon) and added a few more tetras.

There are now eight total Neon Tetras in my 10-gallon aquarium.

They don’t fight anymore and can properly school together.


I've had a fascination with aquariums since a young age. A few years ago, I started to build low-tech planted tanks. My goal is to share my experience to help make yours easier.