"When I get my 55 gallon tank set up, should I still refrain from using the Aquarium salt? I was told at the pet store to use it with each complete water change in addition to the water conditioner."
See, the thing about aquarists is that they fall into different 'camps':
The "use salt always" camp
The "never use salt" camp
The "use salt judicously" camp (my camp)
The "kill everything with anti-biotics" camp
and so on.
You've come to this site because you really care about fish (thanks for coming!). You're going to hear a lot of different opinions about how best to care for fish. You'll learn a lot in the processes. And then you find what works best for you and your fish.
Ok, so I said no to aquarium salt use on a regular basis. I have many reasons for saying this, among them:
diminished medicinal value due to resistant bacteria surviving in salt water
other fish in your tank (like catfish and loaches) who don't have scales can be chemically burned
and I'm sure there are other reasons, but my brain cells are passing out for the night, lol...
"Ps. I have changed his water, left out the salt and I have taken out the plant, as recommended. I HOPE HE GETS BETTER! I Hate seeing him so upset."
I hope he is doing better soon. At least you know there is nothing in his tank or water now that can possibly hurt him, and the fresh water will do him a lot of good.
I have had a few betta illnesses to work through, and some nasty injuries (I had a betta girl whose anal fin was almost completely destroyed. She was in a 1 gallon QT for two weeks, with a water change every day. Not only did she survive... within three days clear tissue began to grown back on her fin... two weeks out, the clear tissue had replaced almost all that had been lost... a month out, the clear tissue start to recolor and at a month and a half, her anal fin is almost completely normal. She also has received a high protien diet, which helps to regenerate lost tissue.)
Again... clean, fresh conditioned water is always your fishy's best friend (next to you, of course)! :)