Larva floating vertically

[keiko]

My first batch of axolotl larvae hatched a few days ago. I've been feeding them and changing the water once a day (tried feeding twice a day, but they weren't interested at all so I decided once a day was enough for now). Temperature is about 19-20 C. Everyone is doing great, but there is one larva that keeps floating vertically a little below surface. It can get to the bottom and can stay there at least for some time, but pretty much every time I go take a look it's floating again. There's nothing wrong that I can see, it just floats there staring up like "hey big head, how you doin'?". So is it normal, am I doing something wrong or is there something wrong with the larva?