Hi new to this but have been fighting stains forever. I have had my well water tested and have received no indications I have metal in the water. Now the problem. I have re occuring brown stains in my fiberglass pool. This year I have tried stain free and metal free with wonderful results. The problem is the stains came back after about 8 days. I have a heater on my pool and I do use soda ash. I have read posts stating both of these may be my problem. I also read on the label of stain free that I should use a non polymer filter agent with my sand filter. What is a non polymer filter agent. I would really appreciate any help. Thanks