Greenish stain in pool

[btolley]

Hello all,
This summer a streak of greenish/brownish stain developed in a line along my pool from the shallow end to the deep end. I assume it's algae, but it is different than other algae I have experienced. A few times over the years I let the chlorine lapse and got green algae, it has always been on the sunny side of the pool, was a green colored film that would produce a cloud when brushed. I was able to defeat it using a less then perfectly executed SLAM.
This new stain is different. Different color and brushing has no impact. I did go after it with a concerted effort of liquid chlorine, caly-hypo, brushing and 24-7 pump. I held the chlorine at about 15.
Is there anything else it might be than algae?
Just an FYI, I always lose .5 to 1 ppm overnight even when i do not see a problem, and yes there is about .5 ppm difference between FC and TC.
Any input is greatly appreciated. Right now I am keeping FC higher than normal to prevent it getting any worse and I intend to SLAM again when the season is over.
20,000 gallons
SWGC
Total alk 90
Ph 7.8
CYA 30

 

[Texas Splash]

Stains in a line huh? Won't budge with brushing? Maybe post a pic or two so we can see it?

 

[YippeeSkippy]

Any chance its copper stains from pouring cheap algaecides in the pool along the edge? Try some crushed up Vit C tablets in a thin sock rubbed on the stain and see if that alters it. Then in another stain area try some dry acid on the stain. Tell us the result.

Maddie