Dark Spots on Ice Skating rinks?

Why are there always dark spots in the ice at skating rinks? Sometimes this occurs right where the line is and the line is completley gone at the part.

Dark Spots on Ice Skating rinks?
I believe that the reason for the dark spots is because the sheet that is beneath the ice that makes it look white is damaged, so the ice in that one spot looks dark.
Reply:The concrete underneath the ice is painted. The owners need to melt the surface and repaint. It also may be some piping that has come through.



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