I added 2# ascorbic acid and have been running filter for about 12 hours straight. The stains have not lightened at all. I'm sure it's iron because I used the vitamin c tablets to test and as they sat on the bottom they made wonderful bright clear spots! There is a blue liner in there after all. I have well water, very low ph, very soft. Perfect water for drinking and showering!
I've got a bottle of Metal Magic ready to go in, but don't know what to do if the stain isn't budging. Add more AA??