I know that lack of information is no excuse, but the fish store didn't tell me everything I needed to know about keeping these guys...as I'm sure they don't tell anyone anything, unless they ask specific questions. It's sad really, they just want to make a sale.
Anyways, after this incident, my wife "convinced" (more like forced) the fish store to replace the dead puffer for free because they did a horrible job of informing us of how to properly take care of it. So, they replaced it for free; however, I had setup a new tank in between all this. The new tank is 40 gallons and is using a Whisper filter rated for 30 to 60 gallon tanks (it'll do a little over 9 full water cycles per hour). I measured the pH, ammonia, nitrate, and nitrate before and 24 hours after I added the new fish, and all is well. I've also started the process of getting his salinity to 1.005ish since the fish store keeps them in freshwater.
It's only been a day, but I already notice that this one is acting different than the last one. I have a dozen guppies in the tank, and he loves chasing them.
Also, I was a bit more picky when I picked out the puffer at the fish store. I had them get the one that I could tell had recently eaten (man was he a fatty). He was also the biggest puffer in the tank...not to mention that I saw him eating food that was in the tank as well, so I know he'll eat.
This time, if anything happens, it will be completely my fault, but that's not gonna happen.

