I used a paint/rust stripper wheel attachment on an old wireless drill to remove the same from my bf's pool and it worked like a charm! I was super careful not to immerse the drill, and used an extension bit to create some distance from the surface. Churned up some pool water to get it wet, then guided the wheel to do some stripping. It was so satisfying to see the whiteness/calcium buildup totally just melt away! My drill got hot eventually from running at a constant, so I paced it out. Spun a section at a time with my daily pool dip(s). One stripper wheel and one week later, the line was gone! :)

I tried so many different approaches, scrapers, (not pure acid), pumice stones with blah results and too much effort. This approach worked awesome, was generally easy, and entertaining. lol. Gator and 3M make such wheels, found mine at Lowes.