Sorry to hog this space mate, I have some wierd residue appear on my alloy wheels not sure if its traps water stain or if the laquer is coming of but only in certain places, would clay bar sort this? I accidently used polish instead of wax but it was this:
http://www.cleanyourcar.co.uk/shop/engi ... p_106.html
Wheels are only 5 weeks old
As for sandpaper I would not use, normally white spirit worked wonders but not sure if will damage your wheels I would test on a small area and if ok, then goes for it