I usually add the metal magic before shocking - but sometimes I get stains anyway. That's why I think I will add double the dose this year. The sequesterant does get broken down by the chlorine over time - that's why you have to add a maintanence dose every week, or every other week. I did add it this year and didn't have stains. One year I tried the cya very low - 30, and had more problems with stains than I did last year when I kept the cya at 50. This year I had my cya between 50 and 70, and had no returning stains after the initial ascorbic acid treatment in the spring. I have not had any stains taking the chlorine up to 25 So I am still trying to find the best way to control the stains. This was the best year ever. I did have my calcium level at 150, and I did use the Metal Magic more often - adding some everytime I added water or had rain. The only thing I can do is to try to kkeep the same chemistry next year and see if it works again, then I will know the things I tried do work. I have tried many different permutations of chemistry over the last 6 years, so if you have any questions you want to ask, just let me know and I will tell you if I tried it, and if it worked - If you do the same we can learn from each other, and will be better able to help anyone else that has a fiberglass pool. One thing that I did notice is that after I did the ascorbic acid treatment, and added more Metal Magic than I had to, the water got cloudy. After the water cleared (there was a lot of chalky substance on the floor of the pool) I didn't seem to get any staining even if the chlorine went high. So a question I have for you is did your water cloud at all? It is just a theory that I have that maybe the stuff falling out with the calcium carbonate gets rid of the metals I am not sure, but I will keep trying to figure out the best way to keep a stain free pool thanks for keeping me informed!