I am reviving this old thread because I just had my stamped concrete deck sealed again. I had major drips down the top of my fiberglass pool above the water line. I used acetone, (the kind you get at the hardware store, not fingernail polish remover), and it worked great. I used a cottonball pad, it removed really easy. Some of the acetone got into the water, I just brought it up to shock level, brushed above the waterline, then backwashed. I had a problem years ago with this and questioned using xylene, I cant remember what I used back then. From my research acetone was okay on fiberglass. Hope this helps anyone with a fiberglass pool!