Slate lost its color & has white chalky look to it

I have a slate floor.  This room flooded about a year ago and what appear to be water marks/stains are left.  A white outline around where a rug was remains, underneath where the rug was still looks glossy and bright and where the carpet was not has lost its color and has a white, chalky look to it.  Is it possible to restore the color to this flooring and is there anything I can use to remove the white chalky look.  I have been told everything from strippers, to acid to paint thinners but do not want to do anything to further damage the slate.  Thank you. 

Is slate in general hard to upkeep?

I saw the perfect color of tile that I have been looking for on ebay.  It is called African Gold Slate Tile.  Can you give some advice on this type of product?  Is slate in general hard to upkeep?

Thanks for your help,

Penni