Stains

[raiderron]

I have 3 year old pool, 18,000 gallons, salt water system with Chlorine generator, white plaster, in Northern California. 2nd summer noticed grey stains, last summer grey stains got bad, tried 2 bottles of stain remover, no luck. Sanded pool, removed most, not all of stains, but stains quickly returned. Last fall and this spring added 10 bottles (over a period of months) of stain remover. I used a PVC pipe to get stain remover right on worse stained areas, and this temporarily improves stains, but stains come right back. Over 2 years Pool builder, "leaves, not brushing enough, your city's water (I had the city test my water, the city's water company strongly, in no uncertain terms disputed this, I discussed with builder and never heard again about my city's water) "lawn fertilizer in pool", we even tried a phosphorus remover. Point is that contractor while verbally supportive, really doesn't seem to know what to do. I also have a worsening orange stain, looks like rust. I keep the pool very clean, chemical tests at builders store are always correct, never had an algae problem. Calcium levels OK, wore out brushes, tried a stainless steel brush, sanded to the point that the plaster feels as smooth as any pool I have been in. I came across an article from a Pool builders convention in Las Vegas that basically implies that stains are / maybe inevitable with salt and plaster. Next step is consulting an out of town professional, already invested lots of money and way to much time. Hoping someone has a solution.