Young Corydoras With Strange Behavior Help

hello. I have been breeding corydoras the past few years, owned hundreds of corydoras, and have never seen this before. I have a free week old fish who has been swimming at the very top of the tank, upside down, or poking at the water's surface. It won't do this all the time, but only every 10-20 mins. There are other corydoras and BN plecos in the tank as well, which do not show any symptoms. Tank is 60 gallon. Ammonia and nitrite are testing zero, with nitrate testing very low. Parent fishes in the tank together are showing breeding behaviour at the moment, so I am doubtful this is water quality issues. Anyone seen this type of thing before?

 

I had a fish do the same thing and it’s because it had a damaged fin. That one could’ve even been born with a deformed fin. They’ll look like they’re swimming fine but when they go to take a break their one fin won’t allow them to hover and they will turn upside down and float while they take a break from swimming. My guess is the lil guy probably won’t make it.

 

Fins all look and seem to be acting normal. Since the fish is so small, could it have been something that it ate? maybe it was eating one of the sinking pellets the adults usually eat, and maybe the piece of pellet is drawing moisture and getting bigger? I have no clue how to even start with this, because the fish's only constant symptom is heavy breathing