It shouldn't come back. What are you measuring your salinity with? There is a good chance that it's either that your salinity is still too high, which would explain the pods living, (not for sure whether they will die in hypo or not.) and why ich is coming back. Or and more likely, it's not ich and some other treatment may be required. First, and foremost. Make sure your salinity is really what it says it is, should be measured with a refractometer. And another thing I just thought of beings though there is rock, and sand in your tank, there is a chance that salinity is different in the holes and crevices of the rock rendering treatment ineffective.