Floating/Sick Cory Cat!!!! Help

[AceTecho]

I just noticed my Cory cat trying he’s hardest to stay down but keeps floating up. I don’t know what’s wrong as the tank is in good parameters. Does someone know what I could be to help him. He’s the only one that’s doing this as he’s in a group of six in a 17 gallon tank

 

[AceTecho]

 

[DoubleDutch]

How long is it in?

Sometimes Corys by mistake or in case of stress can take too much air in their intestials (second breathing system).
In most cases they release this in a certain time and act normal again.

The fish doesn't look ill to me.

 

[itiwhetu]

He looks fine to me.

 

[Colin_T]

How long have you had the fish?
How long has the tank been set up for?
How often do you do water changes and how much do you change?
What sort of filter is on the tank?
How often and how do you clean the filter?

Can you post a video of the fish?
Upload it to YouTube then copy & paste the link here.

Corydoras normally take in a bit of air throughout the day and night to help with their buoyancy and to get oxygen from the air. If the fish swallowed too much air (as suggested by @DoubleDutch), that might cause it to float. Dry food can also cause this.

Stop feeding dry food for a week and offer frozen or live foods instead. See if it fixes the problem. If it does, then just reduce the dry food and give them some frozen or live food each night after they have had dry food.