Same water treatment but one fish is gone...

[locorosa]

I was treating my tank for Ick with the higher temps and salt (kosher). I have 4 goldfish in there and of course my favorite, was toe-up this morning.
Is it possible that the salt water "settled" in higher concentrations near the bottom of the tank, which is where he hung out, he was a huge bubble eye?
I am so bummed by this and I don't know why the other three who are good sized also are totally fine. The only thing I can figure out is that salt water is more dense than regualr fresh and perhaps it settled near the bottom?
I don't want to make the same mistake twice...there are no more bubble eye's but I want to get another one eventually.

 

[DepotFish]

Sorry to hear. It probably wasn't the salt. He could have been pretty well infested internally. He would have been the slower fish, he stayed toward the bottom where there is less oxygen, not to mention the recently deflated eye- so in all he would have been the weaker of your fish.