I am a reseach junkie, but I have only a couple weeks of care until my belt, so take this with a grain of salt; I would just hate to see your question go unanswered
SO! From my research there are a few things that could be going on. The BIGGEST thing you can do to check is just touch him or blow on him to see if he CAN get down himself. If he can, then he is just CHOOSING to float. A lot of the younger ones like to. Additionally if he is super little it might just be that getting to the top for some (extra) air is a hard swim, so floating might just make it easier for him. You can try lowering the water levels, though you dont have to; if you have a HOB (Hang Over Back) filter, lowering the water level is likely to increase the current in the water and that's a no go. My new guy (5-6") would float quite often in the first few days and even now, two weeks later, he likes floating around some times, but is on the bottom\in his cave much more often.
Now if he CANT get down on his own or really has to struggle, then you have an issue. Sometimes the little ones enjoy gulping air and will get an air bubble in their tummy, causing them to float. He could be constipated (watch for a lack of poops\decreased appetite). Both of these things will require fridging with the water level just covering them, so their wee feets can touch the bottom which will reduce stress.
Is there any bloating, floating side ways or upside down?
I expect it is likely the first thing and wont be much of a concern, but let me know!