What are the chemical levels of your pool? If you post your numbers, maybe I can answer some of the questions. One of the only things I can think of is Acid takes metal stain out - that is why it is important to have your ph low when doing a stain treatment. If you had a lot of chlorine, and high alkalinity, then the amount of stain treatment you were putting on may not had a chance to work before it got eatten up. This is just a thought, but with all of us thinking we should come up with some help!