I have several stains on my plaster. They come and go but really have been there for about 6 months or so.
I checked the forum and tried the vitamin c and trichlor test.
Both did not lighten the stain.
They become lighter during sunny day and more prominent earlier or later in day.
I do have an oak tree near the pool however I never let any leaves or other drift stay in pool very long.
I should also note that my PH did get above 8.0 on couple of occasions when I was out of town.
So, not sure if I should begin shock treatment or absorbic acid treatment?
Here are my numbers;
Here are a few pics.
Thanks for any help.