URGENT!

URGENT! help!! Save the one that's left!

OK, this morning I woke up and looked at my tank. The puffer with the weird spot seems ok, but the one that was fine yesterday is in trouble!
The only problems I've seen with this guy was that he puffed up for a long time when I let him in this tank and out of his bag. Other than that and the fact that he was climbing walls he seemed ok. I figured he was just stressed, I put some stress coat in the tank and left him alone. They've eaten like 2 baby shrimp and I think 3 of the baby mollies that were hiding in the tank as I can't find them. The other fish ate most of the shrimp though.
What's wrong with it?!
http://www.youtube.com/watch?v=rZoDr0d3fn0

ETA That one's dead. Help me figure out what's wrong and save the other.

This is the other puffer in the tank (the one with the spot I posted about). Yesterday he was chill and swimming around while the other seemed more stressed. Now he's freaking out.
http://www.youtube.com/watch?v=1OE7BEnNlU4

OK, now puffer that was floating is very very still on the bottom of the tank. Dead things float, right? I'm so upset, yall have no idea how long I've waited for these fish!

http://www.youtube.com/watch?v=5GtO9XurmIE
another video of the one with the bump. My cat jumped on the hand that was holding the camcorder so that's why it jerks at one point.

Yes, I've been reading on these guys in particular for nearly a year, since a friend gave me one not knowing anything about it as a gift (when they started selling them at walmart >.<)
After that I started reading all sorts of articles on these guys. I have had this empty tank for months all cycled and ready to go just waiting for my lfs to finally get some in for me.
Not sure on my water parameters atm, I lost the sheet where I last wrote everything down, but Im about to check again. I know my salinity is 1.018, but I was just about to pull out my test kit to check everything again.

eta:
Amonia is at 0
NO2 is <3.3
pH is somewhere between 7.4 and 7.7, closer to 7.7 though.
CO2 content...not sure. It took either 6 ot 7 drops, and if the pH is 7.7 that means it's 4, which is bad, but if the pH is 7.5 then its 6 ot 7 which is good. So that's a close call. I'm right at the edge there either way. So that's the worst of it I've found so far.

nevermind yall. i figured it out. thanks for trying.

The problem was my salinity. I was retarded and still had my tank set up for a gsp. I made a last minute decision to switch to f8, and assumed they needed the same parameters since they seemed so simmilar. As of now the surviving fish and the replacement seem ok. Surviving fish (Scooty Puff Jr.) is swimming around normally and has really come out of hiding. He's crunching away at some freeze dried shrimp right now. My snails aren't hatched yet, so that's going to be his main diet for the moment. He seems slender still, so I'm feeding him daily for a while.