I read somewhere that the scale that is brown is scale that formed over some dirt. This may have happened over the winter since there was such a calcium drop with high ph. I would do as Waterbear suggested. Take the ph down to 6.8 to 7.0, then brush the surface of the stain - even using a pumice stone. If the area of the stain isn't too big, this should do it, otherwise you will probably have to have the pool acid washed. Let us know how you do