OK I've been wrestling with this on and off for years. I have some staining issues on my liner. In previous years, it affected the white stairs really badly as well. This year the stairs don't looks too bad. The deep end really isn't affected that much except on the corners of the liner, but the shallow end is badly stained. My numbers are as follows:
I'm doing straight BBB and haven't used algecides or any other pool store chemicals in two years. In the past, the pool store told me my copper was elevated. I have a Taylor kit, but no metal tests.
I did a quick 10 minute test of a puck and a sock filled with Vitamin C. The puck didn't clear it up, but it responds immediately to the Vitamin C. Here is a photo that shows the sock slid up off the test spot a bit.
So I assume this is inorganic (metals?) A year or two ago I came to the same conclusion and treated it with Natural Chemistry Stain Free/Metal Free combination. I followed the instructions to the T. It really didn't clear things up very much. I just went ahead and cleaned the stairs with the darn Vitamin C. So what's a better game plan here? For the moment I'm just moving that sock around.