Why is my cory catfish swimming at the top of the tank?

[Why is my cory catfish swimming at the top of the tank?](https://aquariumgravel.com/species/fish/corydora/why-is-my-cory-catfish-swimming-at-the-top-of-the-tank/)There are actually 2 reasons they do this. The first is common healthy behavior, where they see something they potentially want to eat and just