Rust Stain in Pool

I forgot to take the garden hose out of my pool and after about a week my pull had a orangish tint to it.  I told the pool guy and said to buy chewable Vitamin C tablets from Wal-mart and rub it on the stain.  If it works then it is a rust stain.  He was right!  I rubbed it on the stain and the first wipe it was clean as could be.  I dropped a tablets in the pool and they left 2ft clean circles.  I ended up buying 2lbs of some magic stuff to the whole pool instead of random spots.  I thought that was rather impressive.