What is "Jack's Magic"?

[GraceByDesign]

......... Lately I've noticed several small rust colored stains randomly scattered around the walls and floor of the pool. The stains are very small, around the size of a pin head or the tip of a pencil. They won't brush out.........

Waterbear, Aviendha mentioned there is already staining...

[waterbear]

If there are stains try holding a vitamin C tablet on them ..If they disappear let us know and we can help you get rid of them and keep them from coming back. New plaster is prone to staining but the Jack's Magic letter IS a form letter and seqesterant is NOT normally needed on a routine basis.