Just wanted to update on the culator. I have not gotten any stains back since I have it in my skimmer. This is the longest I have gone without stains. I have not put any sequestering agent in since then either. So far for me it works. I have not had to really shock the pool, because the water has been clear all summer, so I don't know what will happen if I do. The ph has drifted up, and still no stains. My fingers are crossed - it will save a lot of money in the long run if this really works.