Just purchased a house in Vegas that has a 7500 gal fiberglass Renaissance pool. The house was a foreclosure and the pool water got very low and very disgusting. It was purchased by a 'flipper' who got the house/yard/pool into good shape and I bought it.

When I purchased, the pool was full of clean water but there are some brown stains on the bottom and sides of the pool. On the sides, the stains have a definite line where I assume the waterline was at the low-water mark. There are no stains above that line. I haven't gotten into the pool yet but a brush on a pole doesn't affect the stains at all. I assume they are stains on the gelcoat from the yucky water, but how do I remove them? Wet sanding?

Also, there is a chalky white substance at the waterline all around the pool. The water here in Vegas is VERY hard so I assume this is deposited calcium/minerals/what-have-you. I tried scrubbing it off with a sponge to no avail. I purchased a product from the local pool supply dealer (Descale-It with glycolic acid) which helped a little but has not eliminated the scale even after 3 applications and scrubbing with a Magic Eraser. And I mean SCRUBBING, as in 80 passes per square inch. Any advice?

P.S. The water chemistry has been maintained properly (to my limited understanding) and is still clean and sparkling.

Thanx!