Walls appear darker than floor, not sure the cause

[Antneye]

I have been using the Pool Math app for three years ever since I got my pool and am very anal about my water chemistry but lately I am wondering if there is an issue. Since last year I have noticed that my walls appear darker than the floor of the pool. I have always chalked it up to shadowing effects but now I am starting to wonder if this is a sign of another issue that is not showing up in my standard water testing. Any and all help or advice is appreciated. See attached pics.

 

[PoolStored]

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