use either water softener salt (rated for being used in a potable water situation) or rock salt.
Aquarium salt is BS, NaCl is NaCl.
you should assume they have all been exposed
a white spot disappears, it means the spot has exploded into up to 100 new ick parasites,
raising the temp, the ick spots mature faster, and this warmth hastens the ick life cycle,
it can take weeks
Hello; All of the above. I would add - do not use salt with any other meds at the same time. -Do not combine meds with each other. (some of these meds do a similar thing to salt)
I will also suggest setting up a quarantine tank (QT) for new fish