Subject: chemical needed to remove contaminate ions from chrome plating bath?

occasional build-up of iron and copper ions in hexavalent chromium plating 
baths <100 to 1 ratio with sulfuric acid> cause a decrease in plating rate.
Using sodium hydroxide removes some of the iron and copper contaminate 
level but adds sodium as a contaminate which is less invasive to the 
process. Is there a better additive or method to remove such impurities?

Re: chemical needed to remove contaminate ions from chrome plating bath?