I've been following and reading for quite some time. I've had issues with algae you've guided me through and now I'm ready to tackle stains. I have 3 different kinds. Two just appeared in the last 3 weeks.
As I've read through much of your site I'd pretty much concluded I had an iron issue. These only started to appear in the last 6 months and they would lighten and darken. The previous owners used Phos Free regularly in the pool which definitely makes me feel that there was an iron issue.
(Within the last few weeks the pesticide crews came through and sprayed lawns. I live on a lake and they are treating the lake for various overgrowth issues.)
Majority of my stains are brownish and are more prominent when my PH is higher. They respond to a vitamin tablet.
Recently I had these skinny copper and curly looking stains appear on the steps. They look similar to a photo I saw you identified as tannin stains. I don't have any oaks. These stains didn't respond to an over the counter vitamin C.
The third stain that's appeared in the last couple of weeks is round rust copper looking. This doesn't respond to vitamin C.
Here are my present levels:
My borates have been running around 30.
I had purchased a bottle of Pink Stuff but had not used it yet.