Removing sealant

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A customer of mine is convinced the patio portion of their pool deck has some kind of sealer on it. Their kids are constantly slipping if any water gets on it. In the picture, you can see its the whiter patio on the left.

Any suggestions on what can remove it? Thad, you mentioned it was “no fun”
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Could be hard water staining - we have it at a bunch of older shopping centers where water has pooled over the years from irrigation, rain and pressure washing.

Hard to tell from the picture, is the concrete stained?