So, unfortunately, at some point in the daytime yesterday while I was at work, our F8 died. So sad. Thanks everyone for all of your posts. His belly had darkened a bit Thursday night...and I did a water change Friday morning before going to work (even though the ammonia/ nitrite/ nitrate was 0/0/5)...figured it couldn't hurt. But he was gone when I came home from work...
SO, my fiance and I were so sad, we went to the local aquarium store to see if they had any F8's...and they did. We wound up picking up a tiny guy

Totally cheered us up last night. He is definitely much smaller than the other two that we had in our 29... but we only got one. So he will have the entire huge tank to himself!!

He's only about maybe a little over an inch...his poor fins are torn up, so I'm dosing the tank w/ melafix.
The store had him in such a tiny tank with two big GSPs...poor little F8!! He also has a visible bite mark on his underbelly (looks almost like a ring mark...guessing it is a bite mark)...but his belly looks decently healthy and rounded. He ate up a shrimp tail like a little piggy last night... I tested the tank water he was in before introducing him into the tank, and it was at 1.002 salinity...Our tank was at 1.006, and I wanted to do a large water change anyway (since our F8 had died), so I brought down the salinity to 1.004-1.005. He seems to be adjusting just fine.
My question is, does anyone treat for IPs right away? His belly isn't sunken. But he's so tiny, it's kind of hard to tell... I don't want to hurt him any by treating him, but I have seen people on this forum talk about treating without seeing any visible signs..any advice?? And also, what do you treat with... With the original F8 we had about 4 months ago (who prompted us to get the 'pufffer only' tank b/c my fiance bought him and put the poor guy into our 55 gallon freswater tank...he got some bad advice at the pet store, and when he started to go off food, that's when I found the puffer forum to look for help...and learned A LOT about how to care for these little guys!)...in anycase, once we got him into his own tank, I think his immunity was so low b/c of being in the wrong conditions for so long, he definitely had IPs b/c he was pooping that 'string of pearls' type poo. We tried to treat him with the Jungle Tabs parasite clear...but he died about 2 days into treatment. I think he was just to ill to get better with treatment...but any advice on whether I should treat right away and what I should treat with would be great. The only stuff I've seen in our local pet stores is the parasite clear...but I can always order something else online. Thanks everyone again!