Just found a super easy way to take the black streaks off

Scrubbing Bubbles and other harsh bathroom cleaners also strip the finish. if you are going to wax again anyway, use Maguires or any quality wax, the the black marks come right off.

I like the lemon pledge idea for between waxings. I'll try that in a couple of weeks when I pull the cover off and start prepping for our June vacation.