betta fish floating up ?

Never been an advocate for Bettas. They are fish that a 5 year old can look into a bowl and say 'OOOoo, pretty fish'. And then Dad flushes him as junior did not take proper care of him. And I think that bettas are terminally abused-tiny bowl, no filtration, no air and food that just fouls the water in a few days. 

If you want to keep fish, there is a whole science to it. Do your homework and give your fish a good environment to live in. 

If you don't know what to look for almost any betta will "look healthy". It sounds like something is clearly wrong. Did you slowly acclimate him and use water conditioner? Properly acclimating means letting the fish bag float in the new aquarium to get the bag water to the same temp as the aquarium water. And also letting a tiny bit of aquarium water into the bag every 15 minutes or so to get the fish acclimated to the new water parameters.

Bloat or swim bladder disease can cause a fish to float to the top and not swim properly. But so can generally not feeling well, being too weak to swim. Look up common bett diseases and how to care for a new betta.

Your fish may be under some stress as it becomes acclimated to its new tank. Assuming that you treated and cycled the tank, and have suitable water parameters before introducing him this is likely the case (if this was done correctly).