What kind of mineral stain is this? This is only the second time I've seen this in a pool. Acid gets rid of it quick and a sock with cal-hypo will actually darken the stain (see the pictures where I drew the letters O and T) I'm assuming the stains are from the frog system that is being used on the pool.
The link is for the photos
https://plus.google.com/u/0/102527211383561562154/posts/hrtkaaCKVRs
The link is for the photos
https://plus.google.com/u/0/102527211383561562154/posts/hrtkaaCKVRs