Ich and temp, and floating

What temperature should water be to keep ich back? I have a 90g tank which
isn't heated but stays around 74 to 75 degrees. I noticed a few grains on
one of my black telescopes. Is the water too cool? Is it better to
Quarantine the fish I see with spots? I would guess it is better to treat
the tank. Is 0.3% salt right, added 3x? Or is this too much? I have read
contradicting statements on this. Some say 1 tsp per 5 gallons, and others
say 1 tbsp per gallon. I assume the 1tsp/5gal is maintenance and 1tbsp/gal
is medicinal? There is a swordtail in this tank, too, which is only 4 months
old and he's never been in salt water. Will this hurt him? I have 2
smaller guppy tanks which I can put him in for now if I have to, but he
thinks he's a goldfish (long story, LOL). I'm not sure he'd be happy with
his own kind.

Also I noticed one of the ryukins starting to "float". Actually, she wasn't
floating yet but seemed to have a hard time swimming. I have isolated her
to a 10g Qtank, added 0.1% salt and fed her only peas tonight, and will give
same in the morning. She has actually calmed a bit but I still notice her
with her tail in the air, so to speak. If she relaxes, she still rises but
she doesn't seem to be struggling like she was before. And before anyone
comments, this fish is barely 2" long, so she's fine in 10gallons. I have
Medigold food. My plan was to feed a few meals of peas only to see if it's
just constipation, and then try the Medigold for a week or so if she doesn't
improve. Any thoughts?

--
} Tammy {
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