My "new" house came with a hot tub. The POs didn't keep the "scale" from building up around the top where the water evaporated and left behind what I think is probably calcium scale. I have tried a number of things (including vinegar and baking soda), CLR and scrubbing with a green pad and Bartender's Friend - the latter seemed to help a little, all the others seemed to have no effect. I scrub and scrub and scrub, but at this rate it isn't doing much good. When the "scale" gets wet much of it fades and then when it dries it comes back (it isn't left over cleanser - just wetting it with pure water makes it fade). It is especially hard to clean where the tub surface is not smooth, which is where most of it is. I had hoped CLR would just dissolve it, but it didn't seem to do anything. Anything else I can try?