Need help asap. Brown stains on side of pool(pictures)

So i have a 20,000 gallon pool and there is many brown stains on the side of the pool. The water is as clear as can be. I have tried using a wire brush, the power washer, a lemon peal and even a rubbed a chlorine tab to see if it was algae, but no luck. Just wondering how to get rid of it.

Here are a few underwater pictures for reference
https://imageshack.com/i/nc39e2j
https://imageshack.com/i/n6ve6fxj
https://imageshack.com/i/np65d2p

Thank you

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