I am observing that some of my 4 week old fry are swimming in a vertical direction...though not all the time, is there anything to worry about? They are in an unfiltered tank with some elodea and hornwort. I carry out a twice weekly water change. Some ramshorn snails are present. They are fed twice a day with BBS.

If they are not doing it all the time, when ARE they doing it?
Are they doing it within a couple hours after you feed them?
What is their behavior when they ARE doing it.
Are they stuck head up, tail down, and they RY to level out, but they can't..
Or are they laying on the bottom, belly flat, head down, and tail up?