Yeah, Freshwater fish just drink a little water and extrete whatever they need in urine. They have more salt in their bodies than their environment does so their kidneys are designed to move more water than salt. Seawater fish have less salt in their bodies than their environment. As such, their kidneys are more specialized to remove salt and retain water. So if you put a saltwater fish in freshwater, it can last for a little while, but eventually it'll drink more water than it's kidneys can
Questionprocess, will become hypOsaline too much water and can kill itself. And of course the opposite is true as freshwater fish put in salt will drink too much salt and not be able to extrete it, becoming hypERsaline and leading to the fishes demise.
Brackish fish however often have more "flex" in their kidneys for lack of a better term and can tolerate varying conditions. It's still not a great idea to push them too far towards the freshwater scale for too long. Now that the ich is gone, I'd start raising it back up to 1.007 if you can and see what happens there., you don't have any sand in your QT tank and only minimal rock right?
