Sick puffer, could be swim bladder?

[E249]

I have a hawaiian blue spotted puffer that had been acting strange. Last night he seemed fine, but today he started to lay around on the bottom. At first I thought he was dead, but when I stuck the net I'm he began to swim. Not fast and scared, but slowly. When I fed them I stuck food right next to him, but he wouldn't eat. I have had him for a couple of months and he's been doing fine until now. I have a lawnmower blenny, a percula Clown, a Diadema, a sail fin tang, and two damsels. None of the fish have been bothering him. When I introduced him to the tank I let him sit for 15 min to get used to the temp and then added a quarter cup of water every min for about 10 min. I recently tested the water and the ammonia was at zero, but the nitrate was slightly raised, but still low. I will test again tomorrow and post the exact numbers. Does anyone know what could be the problem? Could it be his swim bladder?

 

[Innovator]

If it was swim bladder related it wouldn't be able to properly stay bouyant/propel itself. Is it actually laying on its side? Notice any red marks, inflammation, ulcers, growths, white specks (like salt), or tattered fins?