Serpae tetra behavior

[Catfish Lover]

I've got started with 22 serpaes in my 55g at the beginning of September . It's just them and 12 peppered cories. I know they can be nippy with one another but this is usually when the group is too small. Well a couple months ago I noticed one of the serpaes fins were shredded up and looked pale, he eventually passed. Well I noticed today another one looks pretty beat up and is off away from the group. I doubt he last much longer. Do they develop a pecking order and just eventually just keep picking on the weak one until they kill him? Is this going to continue? What can I do about this?

 

[Old Scales]

I've had Serpaes almost as long as I've kept fish (50+ yrs). Although they can be nippy at times I have never had them actually cause that kind of damage. Although when they go into their spawning frenzy I have lost a few at times because of the stress and injury from running into hardscape. The eggs are almost invisible they are so small, so look close. They just scatter them as they dart around. OS.

 

[Catfish Lover]

Any reason how their fins have become shredded then.. I haven't witnessed it but it's pretty obvious he's been bullied and the other that I lost was too.

 

[Old Scales]

NO I'm at a loss there. I've never had mine do fin damage like that. Sorry. OS.