Aggressive WCMM

[Maxi]

So one of my WCMM is crazy aggressive. He relentlessly chases down all of the others, more so during feeding time but also throughout the day too. It's got to the stage where I'm finding all of the others with nips taken out of their fins and other injuries to the point where three have died already. This guy came in a new batch I bought - beforehand they all got along fine.

At first I thought they were just establishing the order - but it has been clear for weeks that he is by far the most aggressive and nobody fights back, they all just try and swim away from him. He's not happy just being the alpha though, and it doesn't look like he's about to settle down. It's been about a month now.

Any suggestions on what I should do? I'm sure the LFS won't take him back because he's so aggressive will they?

Tank is a 55g with 10 WCMM (about 50/50 male to female) and 4 goldfish (2 black moors and 2 ranchus). Tank has been cycled for over 2 years and readings are 0 Ammonia, 0 Nitrite and 20 Nitrate.

Goldfish and WCMM's get on fine and never bother each other. No heater and temp hovers between 22 and 24 degrees Celsius.

 

[Toad]

I'd still try to take it back, the worst they can say is no. Sometimes you just get a jerk fish :/

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[SherLar]

I don't know anything about Whiteclouds, but when I have issues with cichlid aggression, sometimes rearranging the decor works. You could also try removing it to another tank, or even a bucket for a few days. That may allow another fish to claim top spot in the tank, and change the hierarchy.

 

[TMaier]

Last time I had a jerk I gave it to a friend with fish 4x his size. He tried some stuff and got his butt kicked. Then he settled in with them.

 

[nirbhao]

You don't have to tell them why you're returning the fish. Say it wasn't fitting in or, you know, nothing. "I'd like to return this fish. You have that 14 day policy, right?"

You can't train a fish to change its behavior.