Silly cory cats?

[didierlampardcorycat]

'Ello everybody. I've got a question about the cory cats in my boyfriend's 29 gallon freshwater tank. First of all, some info about the tank. As I mentioned, it's a standard 29 gallon, it's been fully cycled, .5 ppms or less nitrAtes, nitrItes 0, no chlorine, pH 7.2., temp is 74 degrees, and it has 8 plants and a piece of driftwood. The current inhabitants are 2 fantail goldfish (under 2.5 inches), 5 albino cory cats and 4 green corys.
The question we have is why the cory cats (all of them) swim in the upper tank levels against the glass a large portion of the time. This has only been occuring since we added the green corys. We have tried both increasing and decreasing the aeration in case they were trying to get air. However they don't seem to be attempting to get oxygen from the top, just swimming along the glass frantically. The cory's in his smaller tank don't do this, they just explore the bottom. Can anyone provide a possible explanation?

 

[Teakwood]

My Cory's enjoy going all over the tank, a big portion of the time they are below but they go up and down a lot. I figure they're just exploring and playing.

 

[tomasm87]

Mine do the same thing. I have 5 peppered and 3 sterbai in my 29 gallon tank.

 

[LS240]

They're just playing. My panda cories do the same thing in my 16g bowfront.