From your picture the white appears to me to be a white pigmented curing compound the contractor did a very poor job of uniformly spraying on the finished surface. I would show the picture to your contractor and ask him if this is the case. If so point out that when applied properly the curing compound should appear uniform “like a white sheet of paper”. Some issues to look out for going forward from improper cure are shrinkage cracks, dusting (a fine white dust on the surface that you can never seem to get rid of) and scaling (flaking of of the surface). Improper cure can also negatively affect strength but in your case that isn’t as important unless you plan on driving on your pool deck. I would avoid using any de-icing chemicals on the surface as these can exacerbate the problems.