I have 2 juveniles that do this too. Whenever I glance in on them, they're resting inside the floating plant, with their nostrils sticking out. They eat fine, act fine. I chalk it up to more axolotl weird-ness.
I clean my sand with a regular siphon. Just stir it up a little bit at the surface, suck up the really fine sand and the poo. If you keep ontop of poo-cleaning with the turkey baster, then you don't have to siphon too often.