I have read all of the posts regarding the use of Oxalic acid you have posted. Thanks to you all for the information. I have a simular problem and have been using OA to combat a brown stain in my pool as well. The OA works great in my 20k gal pool 4 lbs and it is perfect. Problem, even after adding the proper sequestrian agents to filter and backwash the metals. My stain occurs over again slowly after about a week or two. Perhaps Iron cannot be pulled out completely? Is it ok to treat with OA that often? I will check my steps and plumbing for any signs of corroding metal, other than that not sure where it comes from. Perhaps when I add water to the pool?
I use Bromine, and I keep it low and rise very slowly to stop from oxidation. I also have a heat pump, but I do not think the stain is copper. Would copper make this light brown stain?
PH, Akalinity, hardness all fine.
Any ideas or help here would be welcome.