Yes, you will need to closely watch it for cycle. However, there are things you can do to help. Add 100% water from your display, if the tank water quality is good. Add a few cups of sand from your display.
If you are willing to sacrafice a few pieces of LR, you can also add some LR. With hyposalinity, many of the worms, etc., within LR will die off, but the bacteria will remain and assist with tank cycle. You can't add meds, though, or it will kill the LR. If all you do is hyposalinate your QT with the LR, after all is clear the LR can be returned to the tank safely, as long as you have not used any medication. [Only after ich has been cured.]
