Aggressive Goldfish

[HooKooDooKu]

I started my first fish tank about 4 months ago with a common and a rosy red minnow in a 10 gallon tank. As the common grew, I decided it was time to upgrade to a larger tank, so they got moved up to some 20 gallon digs. About that same time, I learned that rosys are schooling fish and that you should keep at least three or more of them, so I purchased another pair, kept them in the 10 gallon for a brief quarantine.

Well I've had all four in the 20 gallon for a few weeks, and one of the new minnows is turing into a bully... even chasing the much larger common. He's become enough of a bully that even DW who doesn't care much about the fish has even noticed. She's already put forth the suggestion that I find someone in the "family business" and get a replacement.

I've wondered if I just need to give him some more time, bully him myself a little bit at feeding time, or add a few more rosys to help spread out the aggression.

Suggestions?

the bullying and
I have a 20 gallon tank with one common goldfish and three rosy red minnows. We started with just the common and a

 

[peaceablegarden]

I had a bullying problem with a Neon Tetra. I broke it up by adding a couple new ones. I understand sometimes it works and sometimes it doesn't. In this case it did, but the bully died a couple of weeks later for reasons unknown.

 

[jsoong]

Maybe that rosy is a male? The safest is to exchange the fish if possible. Getting a large school (like a dozen) might help, but that might be more fish than your tank can handle.

 

[HooKooDooKu]

Maybe that rosy is a male?

How would I know (and what difference would it matter in terms of what to do next).

He came from the local PetSmart. Given some of the stupid "Corporation" mentality they have (for example, they sell 29 gallon tanks... but only with a cheap $20+ hood that does you no good if you wanted a planted tank), I would likely expect that they have a policy of not taking fish back.

In other words, if I take the fish back to PetSmart... I get the feeling that won't be any different than if I hand him off to someone "in the family business".

 

[HooKooDooKu]

And if I did get more fish... I thinking along the lines of adding two more (three max). That would make for a total of one common and 5-6 rosy minnows, two ghost shrimp, 6 amano shrimp, and an unknown number of MTS in a 20 gallon tank.