"staining" on bottom of pool

[ddag]

I have an in ground saltwater pool with a bluish pebbletec. I have what appears to be a brownish staining on the pool bottom. It does not feel slimy but cant seem to brush it away.
Any idea what this may be?

 

[zea3]

Welcome to TFP! Could be tannin stains from leaves if they have been there a while, or could be iron stains. Do you use well water to fill your pool? Could you post a complete set of test results?