Light green stains on walls?

Ok so two months ago i had back to back green algae breakouts, my cya was very low so the pool could not hold any bleach. now my cya is @ 60 and i keep the chlorine constant @ 4ppm. but ever since the algae there has been a light green tint to my diamondbrite walls no matter how much i scrub them it doesnt go away. Is there any advice? In the pool shop i did see this small stone for taking away stains but it was very rough and i figured it would destroy my diamondbrite also it was tiny so it would take me hours to scrub the walls by hand. Thanks

Also i tried shocking the pool to 20ppm and scrubbing the walls but it didnt help.

Give us a complete set of current water testing results, please. You probably just need to shock your pool and hold it there for a few days and that will take care of it. Try to sustain the high reading without letting it yo-yo up and down. Also run your pump 24/7 and continue brushing the pool daily.