Persistent dirt above the waterline

Welcome to TFP.

I do not know what your pics are showing. Can you post some wider shots of the entire pool?

It may be mold or mildew. If a pressure washer has not cleaned it I am not sure youc an without damaging the liner.

Is that a vinyl liner? I assumed from the photos it was plaster and ‘polyester’ was an autocorrect for ‘plaster’. It would be good for @zoltym to clarify a few details about their pool.

zoltym said:

I try to clean it by soap and brush also Bayrol Bordnet and pressure washer.

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Also, I wouldn’t use a pressure washer on a vinyl pool, so plaster assumption seems appropriate.

I think picture is upside down and blue area is lower part of wall.

zoltym said:

Anybody can't help me?

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Sorry you're going through this but from here nobody can help you, but on your own try various products as we're not familiar with what's available as far as cleaning agents to give you a recommendation. Start with the least aggressive and step up your game until you find the product that works. Best of luck.

You may want to do some searching about polyester pools on the internet. I had never heard of a polyester pool so I did a quick search. Here’s one quote I found:

“Polyester pools are ephemeral pools because of all the disadvantages that we explained above. The exposure to the sun will contribute to have some parts discoloured. Is this what you want for your pool? Well, that over time (not too much) it will deteriorate and you will have to solve some aspects in which you may invest money.”

Like I said, I don't know anything about them and don’t know if that quote is true or not, but maybe if you could find other people who have that type of pool you could share your experiences. You’re the first I’ve seen on this forum with a polyester pool, so I don’t think you’re going to find anyone with experience here. Maybe I’m wrong and someone will chime in. In any case, sorry about your pool and I wish you the best of luck at sorting it out!