Salt helps cure ich, but I`m not sure if it can fix it all on its own. It`s also recommended you raise the temperature of the tank, and use malachite green for 1 week. Don`t stop treatment early just because it seems to be gone. Because of the life-cycle of the ich parasite you need to treat for a full week to be sure you got it all. Raising the temperature in the tank speeds up ich`s life cycle, which helps make sure you got it all in that week. I was lucky and all 10 fish survived. Though I wonder why I was treating feeder fish, anyways... Since then Lloyd has eaten two.
To the best of my knowledge, turtles can`t get ich. Lloyd was unaffected by it. I removed him from the tank and put him in a pitifully small tank for a week, though, while I treated the fish. I`d heard that malachite green can be used to treat fungal infections in turtles, but I wasn`t sure if the concentration of malachite green in the tank was safe for Lloyd or not.
I also recommend removing any plants from the tank before treating fish with malachite green. If the plants absorb the medicine, that might not be the healthiest thing for your turtle to munch on.
Good luck.
~Rachael