We have lived 4 years in Phoenix area and own an Inground spa. I just drained it today and notice a whitish cast to the pebble tec coating. Since the spa is empty, what can I use to remove this calcium(?) buildup before refilling the spa? Also, I scraped the waterline calcium buildup away, but still have a whitish shadow where it was. Tried pumice stone to no avail. This is our first time owning a pool or spa! Thanks for any help/suggestions!