gs/aristo junction produce grille owners... help

i have a JP billet grille on my 2nd gen gs. it's a daily driver so it's outdoors a lot. i'm having a tough time with hard water spots on the black anodized portions of the horizontal bars. 

i'm wondering if i am an isolated case, or are others out there having the same problems i am? 

or can someone offer up a solution as to how i can get the spots out???

i've risked using both chrome and aluminum wheel polish to no effect, only to have the black anodizing come off my my polishing cloth (gasp!)...