OK. Well I have some of that. I did try a 4;1 dilution as it was recommended by a pool supply store, but it didnt do anything. Straight w/no dilute........OK....well......ill have to very careful and give it a go on a test spot to see if it works first.
Ill let you know what happens. So far Ive gotten tips to use.
Bleach,
lithium hypolate in this thread,
4;1 muriatic (did not work),( But did an excellent job of cleaning a copper weather vane I just did.)
full strength muriatic
I can try 1 and 4 easily tonight and let you know.