Corydoras not one of the cool kids?

[Sublimer]

I have 3 peppered corys in a 20 gallon long with 5 platies and a small clown pleco. They all get along and everything looks good but I've been noticing some behavior that I'm unsure of from one of my little guys. Every now and then 2 of my corys will stick together and one will be the oddball out chilling on his own. Sometimes I think he doesn't appreciate being a third wheel. I know corys feel more comfortable in larger numbers but I don't want to overstock the tank. Would it be okay for me to add one more? And does it strictly have to be peppered or can I try a julii?

 

[Rivercats]

While cory's enjoy shoaling with their own species they will shoaling with other cory species. But remember shoaling isn't schooling. Shoaling fish are fish that swim closely together and in a similar direction but individuals may go out and scavenge alone.

 

[Coyne]

Is it possible the two that are going of together are spawning?

As far as adding another goes... Im not sure what kind of filtration you have, but if you have the bare minimum you could probably stand to add another cory.

 

[Sublimer]

I'm assuming this means he's okay. It's just I notice the pair is more active with their environment while the loner will often just gaze into the distance. As I type this though he's rummaging through the sand with them. I'm worried that he isn't getting a sense of community like he should

 

[Coursair]

If you have room add more of the same species. I don't add a second species unless I have room for at least 5-6 of each kind.

Most C julii btw are actually C trilineatus. Often mislabeled.