White grey smooth layer on walls and bottom of pool

[JarekZ]

Hello we have 4th year pool that we started to see in 3rd year creating layer of smooth white grey on walls and bottom, all under the water (visible on pictures attached). This layer is not possible to clean by brush or finger. Some areas are more visible some not. Maitenance company said this is kind of "sediment" and on third picture they tried some kind of accid to clean that helped (because this method would be too harsh they did not use this for whole pool). Early this year they reduced pH to about 4 or so and then get it back to normal 7,2 which helped to clean pool. But this layer build again in few weeks early this year when we started session.
We have water treatment automat to keep pH, Algicide and create chlorine so these are controled and calibrated by the company.

Any idea what it is and why this is build again and again?

 

[mknauss]

Welcome to the forum!
Tell us about your pool. What test kit do you use to monitor pool water chemistry. What are your current pool water chemistry results. What chemicals do you use to manage the pool water chemistry.
I suggest you read through Pool Care Basics - Trouble Free Pool and even look at a few of our videos TFP-TV - Trouble Free Pool