Cory cat schooling

[GreenTerror7]

So I picked up 3 panda cories and 3 sterbai cories to see how they do in my tank. They seem to be doing well and it seems like the two different species are schooling together. Is this because I haven't added enough of the same species yet or will they always do this? I would either want to make two schools of 6 or keep this one mixed school.

Side note, I don't have very much experience with Cory cats and I was wondering if it is normal for them to swim vertically against the glass, they don't come all the way to the too but they just go up and down the sides sometimes, is this normal?

 

[Coryloach]

When they are moved to new tanks, they tend to be a bit restless and swim upside down for a few days. It's stress related and typical for them. It's nothing to worry about it, sometimes the move even triggers them to spawn.
They'll settle eventually. That's not schooling though so even though you see all of them running around now, once they get adjusted to the tank, they will most likely keep to their own species so I'd up each school to 6 as you suggested. I have 3 sterbai cory with 30 aeneus corys and the 3 are always together except for feeding time. Also, half of the aeneus are albino, the other ones green and they too segregate themselves by colour and each group occupies the opposite side of the tank. But like all corys, they do get on well together otherwise.

 

[Wailua Boy]

I think in the wild, you will find mixed species of Corydoras schooling or at least shoaling together on occasion.....

 

[Coryloach]

In the wild otocinclus school with corys for protection, yet I wouldn't be adding otocinclus as part of a school of corys.
Some species of corys are very closely related and will mix together but these can also hybridize hence you don't want them in the same tank. Other species of corys are so distantly related that they don't recognize themselves as the same type of fish. But I agree, if one doesn't have a choice, better keep corys with corys. But since we have the choice what to place in our tanks, better keep a sizeable group of each cory species and don't make your tank like a Christmas tree.
Corys are social fish, not a schooling type of fish, so they are happier when in a good group of their own species.