White area on grey hydrazzo pool floor.

Hello. My pool is seven years old with a grey hydrazzo finish. Pool company opened it this year and I have a white stained area in shallow end. I can't brush it off. I poured acid in and tried to brush but it's a couple feet deep. Water's too cold to get in right now.

Could cal hypo shock bleach the grey hydrazzo if it was sitting on bottom? Or is my hydrazzo already wearing thin?

Thanks