plastic parts are kinda yellow

[engrav]

Hi
Had an algae fun time Aug 2013 one year ago when I departed for 3 days and left the back wash valve up.

Yes, I did that. You guys helped me fix it. Was a mess.

Anyway
Various white plastic parts turned yellow, like skimmer floats.

Now pool is clear and all is fine but the previously white plastic remains kinda yellow. Some of it wipes off with a rag but hard to get out of small spaces.

What is this stuff?
How to remove?

 

[JasonLion]

That could be pollen related, or possibly iron staining.

 

[engrav]

That could be pollen related, or possibly iron staining.

Thank you
Had well water tested long ago so dug out old results, no iron
but we have tons of pollen so that likely solves that

and in another thread you said
"Many kinds of plastic will yellow over time. After a long enough time some kinds of plastic will turn a dark yellow that many people will call brown."

so I guess I will just ignore it

thank you