Hello! I moved to a house in northern California 5 months ago with a pool that I think is at least 16 years old. I've been learning a lot thanks to TFP and the water looks great, I test it all the time and take it to the pool store weekly. But the pool has had these stains near the main drain since the day I took over. I'd love to get your thoughts on what you think this is and if it's a concern.
Thank you
Thank you