Mothers Chrome Cleaner! I use that on my tips and they come out looking brand NEW. I hadnt cleaned my tips in months and with a new O/R H, my tips were dead black inside and the outside edges were full of black spots. I used a cloth with the mothers and worked at the tough spots and everything came right off. They look super clean now, I def recommend it!
Try using Eagle One Never Dull. Its a chrome and aluminum cleaning polish. I use it on my stainless tips(stock) and it works great.It comes as a rubbing cloth. You polish to a haze and then wipe off excess and BAM!