Swimbladder again

Hi - I am new to groups, so here goes.

I have a Ryukin with swimbladder problems, I think.
My husband brought him inside from our pond on November 15th. He was
floating on top and my husband didn't want him to die as ice was
forming on the top of the pond.
(We have 3 koi outside that we pretty much ignore except to feed once a
day when they are interested and to do a 1/2 water change to the pond -
which is set up with 3 small waterfalls and gravel filter) This fish is
the only surviving goldfish and is a baby from the original Ryukins we
purchased along with the koi in 1999.

Anyway....So, we were suddenly into becoming indoor fish pet people.
I purchased a 29 gal tank - whisper power filter and
heater.

Tried a bacterial treatment initially. (Of course, I didn't realize
about the tank cycling and the ammonia shot right up).
But, he lived through that. SO, I purchased all of the necessary
bottles of 'stuff' for testing Ammonia/Nitrites/Nitrates/PH.
I also did many water changes and Ammonia is zero now and nitrites
then shot up and are now about a 2 on the test sheet.

I have tried giving him -
1) very small sinking pellets,
2) peas (coaxing him with it on a toothpick),then using an eye dropper
to get it into him. He spits most of it out!
3)I have tried using an eye dropper to get thawed shrimp brine into
him.
I have yet to see him go for ANY food on his own. For some reason, he
is still alive.!

Two weeks ago, I tried a fungal disease treatment for 4 days. He just
became very lethargic. I have tried moving him to a bucket and doing a
15min. epson salt bath.

He is still swimming upside down or lying on his side at the top of
the aquarium. He does get these spurts of activity and dashes about,
though. I don't want to give up on him.

FINALLY... to get to my question...
I recently read a post in this site from someone who
said to
- raise the water temp to 85 degrees and then
add 1 teaspoon of epsom salts to each gallon of water .
Do this for 48 hrs. or so.
Then, do large water changes for the next few weeks to get
rid of the epsom salts.

Why epsom salts? Why not use Aquarium salt? Will I have a better
chance with epsom salts?

Thank you.