Sorry to hear about your puffer.
This could be stress related and maybe caused by a drastic change in salinity from one side to the other. You did say the salt water level was too high from the LFS
? So, how high was it in your tank? Most importantly, if it was very high and you adjusted the salinity back down to an acceptable level too quickly, this would surely stress him out or possibly put him in shock.
the best way to put him out of his misery is to place him in a bag half full of water from the tank. Use one of those bags from the LFS
if you got one, and seal it up just like they do. Then place him in the freezer. As he starts to become cold, he will fall asleep, and then drift off into unconsciousness.
I have had to do this a couple of times and it is hard to lose a loved one like this. But it's for the better. If he's not eating, just drifting if you move him, then help him along. You will both feel better.
29gal BB | 42+ lbs LR
| 143watts PC
| Asst. Leathers, Frogspawn, Hammer, XLG Open Brain, Zoanthids, Mushrooms, Diploastrea heliopora | Blue Mandarin | Atrosalarias Fuscus | Pair Captive Bred Ocellaris Clowns | Peppermint Shrimp | 6 Astrea's |