I had this exact problem! I used a little baking soda to gently clean the sides of my tub, gave a good rinse and then added fresh water. The next day, the whole tub felt like sandpaper, as mentioned above. Learning that it's scale makes so much sense, as how could just a little baking soda make such a mess?! What I'm hearing now is if I just lower the PH using my PH- powder (which will also bring down the alkalinity) the scale will "dissolve" back into the water. Nothing else needed? We did use soft cloths to gently rub some of the scale off, but I worry that it could do damage. Yikes.
