Long Fin Danio's Aggression?

[rpgmomma8404]

I bought five long fin danio's for my 15 gallon. Two leopards and three zebras. They were doing pretty good but now I think one of the leopards are picking on the other ones. One fish has most of his caudal fin almost gone and seems to be missing scales near that area. Then I noticed another fish whose tail was perfectly fine starting to show the same problem. The two leopard danio's seem to be doing fine but all three zebra's just seem to be kind of loosing their caudal fin. Although one was missing half of his when we got him but he was getting around perfectly. Did I not get enough of them? I know they are a schooling fish but I figured five would be fine for that tank. I tested the water yesterday and the only thing I got from it was between 10-20 ppm nitrate. 

 

[rpgmomma8404]

Never mind, we took them all back. 

 

[Ninjouzata]

I'm sorry not really sure on the agression..I wonder if it was maybe too many males to females? 
But they're not meant for that size tank anyway as they are so very active, most would like to see them in a minimum of a 4 foot tank, so I suppose it's good you took them back!

 

[rpgmomma8404]

I'm sorry not really sure on the agression..I wonder if it was maybe too many males to females? 
But they're not meant for that size tank anyway as they are so very active, most would like to see them in a minimum of a 4 foot tank, so I suppose it's good you took them back!

 
Yeah, I'm not even 100% positive after everything I've read. Probably right on the lack of space. One ended up dying and the two other zebra's were starting to look pretty beat up. Looks like it was the two leopards that were bullying. That's okay. I rather have them out of the tank then all of them end up dying or bullying any other fish.