Our pool had some residual staining when the flagstone coping (mortar) and concrete decking were poured. To remove the stains that ran-down from the edge to the waterline, we used various products readily available, but always started with the least aggressive. For example, you start with a 50/50 mixture of water and muriatic acid. Spray it on the area, rub gently with a Scotch-Brite pad, then rinse. If that doesn't work, you might try a Magic Eraser, then some 1,000 grit wet/dry sandpaper. If needed, you should be able to use 600 grit wet/dry. The wet/dry sandpaper was recommended by our installer as well. But be sure to speak to your installer first before using anything. For warranty purposes, they may chose to have the concrete sub-contractor take care of it first. If you do end-up doing it yourself, do a small test area first and let it dry to ensure you are happy with the results. Remember that over time, our FG gelcoats will look a bit faded above the waterline (normal), but since yours is so new you may chose to use a fiberglass polishing compound to give it a like-new shine if needed.