acid wash pool
You could wash your pool walls with pool acid.
What kind of stains? Magic Eraser takes off most stains.
try oops! or goof-off
It sounds like some sort of algae when you expose it to the pools water it brings it under controll.
Just scrub with a rough sponge
clean it with peroxide
Have you tried muriatic acid? be careful with the stuff though.
I would think you could use "Oops!" or "Goof Off", which are liquid emulsifiers and do a good job of dissolving various glues. You will most definitely need to wash the wall after you get the "sticker stains" off.
i only found this answer:Try a chealating agent -- a liquid stain remover. It may take two quarts to do the job. Follow the mfg's instructions.
Green stains (copper color) that cannot be removed indicate you might have a pH problem. K
A lot of scrubbing and some chlorine