I have a person I work for as a personal assistant. She has a 25,000 gal chlorine pool with some dark stains that popped up about a year ago. She says she has had pool people come out and they just say they don't know what it is. We performed one of those Jack's Stain ID kits and got no results from any of it. So we are working to try and identify what this is. We are open to suggestions on how to figure out what stain this is. Located in Dallas, TX.