Lulu,
Axies do have a swim bladder, there is a thread going on somewhere at the moment about this topic.
Im not sure what could have made him start floating, but axies do this from time to time. All 3 of my axies also 'blow' bubbles when sat on the floor or the tank.
It is very possible that he has air in him that is making him float.. your best idea to stop him from getting anymore stressed is to find a small container and fill it up so there is just enough water in there so he can stand up.. (make sure its tank water! If its shallow container though make sure it has a lid or you can cover it up, some axies may jump when startled.
Take him to the vet still though, he maybe able to help you out more.
As Claire said there is no need for the salt baths as he ha no infection that we know of.
The small gravel may be a problem, if they eat too much it can block them up, and some have been know to die.. You best best is to remove the small gravel and replace it with either sand (which ive had alot of sucess with) or large river stones or anything that CANT fit in there mouths.. anything that can they will eat!.. or if u cant take the small gravel out at the moment cover it with larger rocks/slate.. so they can eat it!
Good luck.. let us know how it goes!
(Message edited by jigglypuff on March 02, 2005)