I just wanted to follow up and say that the last thing I had tried was throwing one bag of shock in the pool, and it immediately turned brown again. I took a sample to the pool store, and they said just a tiny amount of copper again. I bought some intensive metal treatment, which I have added to the pool. My plan is to let the treatment filter through for 24 hours and then I will vacuum the pool and change the sand in the filter, since it is due to be changed anyway. Does this make sense? Also, if by some miracle this does work, what do I do about topping off with well water? Won't that just put the metals right back in?