SteveJ, if the spots won't come off with Windex multi purpose( which Humminbird recommends ) then try this. Dampen a paper towel in white vinegar, lay it over the screen and pat it down where it is touching the screen all over. Let it set about 30 minutes then remove and rinse. Will take hard water spots right off and not harm screen. I have seen a few where it took a couple of applications but rarely.