Rainbowfish Terror

Hello, I've got a fully cycled 120gal planted tank which has recently been terrorized by a turquoise rainbowfish.

In my tank I have:

2 pearl gouramis (female)
1 blue ram (male) (he thinks he's a pearl gourami and schools with them)
1 Betta (male) (don't crucify me, he's been a part of the community for 6 months with zero issues)
6 black kuhlI loaches
6 black neon tetras
6 turquoise rainbowfish
3 Armano shrimp

Everything was peaceful and great. I had the 6 juvinile rainbowfish in quarantine after getting them from the LFS, but unfortunately my qt tank is only 20 gallon so things got tight and they started getting agitated so I decided to put them in the community tank after ~2 weeks.

In the community tank, the biggest of the rainbowfish has developed deep beautiful colors, but also a nasty attitude. He is constantly chasing the other rainbowfish and tetras, breaking up any schools that form. He especially seems to be picking on one rainbowfish in particular, who is developing white marks from bites I'm assuming. They have been in the 120gal for two days now.

So I have two questions.
1) is the mean rainbowfish just trying to stake out his territory in the new tank and will calm down?
2) if I need to separate the hurt rainbowfish to treat the wounds in qt, will being alone in the tank cause more stress in this fish?

 

Hello, I've got a fully cycled 120gal planted tank which has recently been terrorized by a turquoise rainbowfish.

In my tank I have:

2 pearl gouramis (female)
1 blue ram (male) (he thinks he's a pearl gourami and schools with them)
1 Betta (male) (don't crucify me, he's been a part of the community for 6 months with zero issues)
6 black kuhlI loaches
6 black neon tetras
6 turquoise rainbowfish
3 Armano shrimp

Everything was peaceful and great. I had the 6 juvinile rainbowfish in quarantine after getting them from the LFS, but unfortunately my qt tank is only 20 gallon so things got tight and they started getting agitated so I decided to put them in the community tank after ~2 weeks.

In the community tank, the biggest of the rainbowfish has developed deep beautiful colors, but also a nasty attitude. He is constantly chasing the other rainbowfish and tetras, breaking up any schools that form. He especially seems to be picking on one rainbowfish in particular, who is developing white marks from bites I'm assuming. They have been in the 120gal for two days now.

So I have two questions.
1) is the mean rainbowfish just trying to stake out his territory in the new tank and will calm down?
2) if I need to separate the hurt rainbowfish to treat the wounds in qt, will being alone in the tank cause more stress in this fish?

Rainbows are great fish, but they are definitely territorial. They are also not natural schoolers in the wild. Normally the fish that's getting picked on would swim away, but he can't...he's in a tank. Go ahead and quarantine him so he can heal. The aggressive one has already developed his instinct to establish dominance, so he'll probably just find another one to pick on. Putting an aggressive fish in quarantine for 2 weeks by itself has worked for some people to calm the aggressor down. But with rainbows, another dominator could take its place. My opinion is that you have too many rainbows for a peaceful tank. My suggestion is to find new homes for all the rainbows except for 1 male and 1 female.

 

Rainbows are great fish, but they are definitely territorial. They are also not natural schoolers in the wild. Normally the fish that's getting picked on would swim away, but he can't...he's in a tank. Go ahead and quarantine him so he can heal. The aggressive one has already developed his instinct to establish dominance, so he'll probably just find another one to pick on. Putting an aggressive fish in quarantine for 2 weeks by itself has worked for some people to calm the aggressor down. But with rainbows, another dominator could take its place. My opinion is that you have too many rainbows for a peaceful tank. My suggestion is to find new homes for all the rainbows except for 1 male and 1 female.

Everything I had read before getting the rainbows said to get at least 6 because of their strong schooling instinct. So this isn't accurate and everything would hopefully get better if I had fewer?

 

Everything I had read before getting the rainbows said to get at least 6 because of their strong schooling instinct. So this isn't accurate and everything would hopefully get better if I had fewer?

They school in nature by somehow choosing who to keep in their schools and who to chase away. There are many fish that school in nature well, but in tank conditions, they many times develop a dominant member. The other choice I could suggest you try is quarantine the aggressor and see how the rest of the rainbows react. You may only have to rehome him or even see if he calms down after being quarantined for awhile.

 

They school in nature by somehow choosing who to keep in their schools and who to chase away. There are many fish that school in nature well, but in tank conditions, they many times develop a dominant member. The other choice I could suggest you try is quarantine the aggressor and see how the rest of the rainbows react. You may only have to rehome him or even see if he calms down after being quarantined for awhile.

I understand, thanks so much for the help!

 

I've been keeping Rainbow fish for 10 years now and have found them to be peaceful fish. They are a schooling fish and should be in groups of at least three. That said, not all of my Rainbow fish species are in schools of at least 3, but they do seem to all school together. Also all eleven of my Rainbow are males.

It is possible that your aggressive Rainbow is just a bully. All fish have different personalities. So you may want to consider rehoming him and see if the tank settles down.

Best of luck.