I have a 11-year old fiberglass pool. I’ve periodically had stain issues, and had been successful with them in the past using Jack’s Magic Stain Solution #1 (“the iron, cobalt stuff”). But I had some areas of relatively minor discoloration that it didn’t successfully treat. I read on various forums including this one testimonials from people with fiberglass pools who had great success using ascorbic acid once a year at the beginning of the year – they said it made pool look brand new again.

SO I tried it – pool water pretty well balanced, and chlorine under 1PPM. Water pretty cold – about 58. I used 1.5lbs of Ascorbic Acid (using brand “Natural Chemistry Stain – Free”). Very quickly some yellow stain streaks appeared on steps and near edges of pool – seems that the acid caused something to come out and into pool sides. It does not brush out.

Thinking it might be iron, I tried some of the Jack’s Magic Stain Solution #1 at one spot – but no success.

Ideas as to what the acid caused to happen, and more importantly, how I can recover ? (MY pool looked much better BEFORE I tried the ascorbic acid. I of course wish I had just left well enough alone.)

Thank you.