Pictus Catfish glass surfing

One of my three pictures catfish I noticed is glass surfing but only when the lights go out. During the daytime they seem to act normal scavenging all about the tank looking for food and exploring. The tank is cycled I've had it for about a month now I've done my first water change the day I got to pick this catfish was about 3 days ago. Before I did the water change my levels were good ammonia was zero, nitrates were zero, and nitrates were also just about zero. I also cleaned out my fluval FX4 filter for the first time it was pretty gross. After all of that cleaning I then added to pick this catfish. A couple hours later one of the three Catfish ended up getting a bloated belly out of nowhere and I put it in my hospital tank with some Epsom salt for about 10 minutes then put them back in the main tank and then the next day the belly actually went away to my surprise. But now I am seeing one of the three glass surfing but only at night does anyone know what this means?
And I ment " Pictus Catfish"

 

Catfish typically gulp water for their intestine, not labyrinth (it can breathe air directly) and the air bubble is held just under their mouths, in the chest area. The bump goes down as the catfish uses the oxygen.

At night, they typically go wild and swim everywhere. This is normal for corydoras and nothing to stress about.

 

Pictus Catfish is a corydora ?

 

Ooo Pictus and Picture got messed up together… with you now!

I’m not too familiar with Pictus but reading online, it says that it will be skittish/energetic, if isn’t comfortable with its surroundings or stressed.

 

Catfish typically gulp water for their labyrinth (Organ that can breathe air directly) and the air bubble is held just under their mouths, in the chest area. The bump goes down as the catfish uses the oxygen.

Catfish that can breath air do not have a labyrinth organ, only gourami, bettas and their relatives have that. Corydoras and other catfish breath via specialised parts of their intestines.

Edit: Glassurfing is also normal for stressed or sick fish, especially catfish have a tendency for it. Please use the emergency template so people don't have to ask too many questions.