First, a thank you.....I have been a pool fool for years, blindly doing whatever the local pool store told us to do. I discovered your site last Fall and am a total convert! Just finished our first ever SLAM with $50 worth of liquid chlorine as compared to the $2-300 we usually spent on chemicals recommended by the pool store each Spring. So a BIG thank you. If we manage to keep our jobs during the pandemic, we will be sending in a donation later this month. Now my question. For several years we have been plagued with brownish reddish staining of our steps and liner. Based on some research last year, we learned it could be copper, so we disconnected our heater and went through a successful polyquat/ascorbic acid/Jack’s Magic/C-U-lator process to clean it up. But, the staining is now back again this year. Tested water for copper (LaMotte Copper test kit) and results are zero copper in the water. However, testing with Vitamin C tablets shows complete removal of the stain in just 60 seconds which I thought means it is copper. I have attached some pictures taken during the Vitamin C testing. Any thoughts on what the stain could be? We have a massive oak tree and many pine trees around our pool. i know these can cause staining, but would Vitamin C clear it up?