With that title, I am not complaining...but want to post this for comment: So, for the last two years I have noticed a "charcoal grey...dark stain" in the deep end, on only one side of the drain, on the order of 3 feet by 2 feet, sort of a kidney bean shape. If I search, I can probably find a photo taken after SLAM on a calm day....with still water. Clearly evident. Would not brush off, was not dirt or organic in nature. Assumed but cannot prove it was Iron, but prior to opening this season, I had bought some VIT C tabs was planning to use them on the "Iron Stain" in a weighted sock this week. So, I opened my pool within the last 7 days and after SLAM and all the grubby organic matter has lifted off the bottom, I am happy to report I noticed the stain is gone. No complaints, but I also assumed naturally the iron had gone into solution with the water...Since I needed to test for Salt content at the Pool store (and get needed muriatic acid)....and their standard water tests for Iron and Copper.... To my surprise....both were 0 ppm. Not 0.0001 ppm, but 0.000. Now, last year when I closed the pool (October) I know for sure I have non-zero Iron and Copper. I just assumed the number for Iron when I opened would be a bit higher due to the stain being gone. But, no!!! It's Zero. So, I am at a bit of a loss to account for BOTH the (assumed) Iron stain having vanished over the winter and B) having the pool store reading at completely nothing for the Fe/Cu Metal content...Ideas? Now, what to do with the VIT C? I guess I can consume it... LOL>