Fertilizer from wind in pool , need to be concerned ?

If there is iron in it I agree. If not, then it will be fine. Keep your FC well above minimum, maybe just raise it to shock level for a day or two to oxidize the nutrients.
 
+1 to everything above. If it were mine, I'd brush the bottom well, a few times, to hopefully dissolve the powder you can't see. Good chance there will be no problem, but getting spots of iron stain would peave me off too much to take a chance.
 
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