[Cougra]

I'm uncertain if it'll do the puffer any harm, but I would keep an eye on it. The main problem I can see this causing is if it constantly has air in it's system it will put extra strain on it's swim bladder to compensate for the added bouyancy of the fish. In a healthy fish with a strong swim bladder, this shouldn't be a problem, however if the fish gets weak or there is something wrong with the swimbladder, then you could have a problem with the puffer not being able to maintain nuetral bouyancy and it will need to struggle to be able to swim tothe bottom of the tank. This problem is known to occur in a few types of freshwater fish and I have seen some tank breed clownfish with similar problems, however this is associated more with constantly feeding them at the surface and they gulp too much air. If it does happen, the best thing to do would be to remove the airstone and feed the fish below the surface of the tank. Eventually the extra air will pass through the fish and it'll be able to maintain neutral bouyancy on it's own.