Q.: I want to use diammonium citrate to remove discoloration from newly placed concrete. I've called chemical-supply houses and pharmacies, but no one seems to recognize the term. How do I find this material, and how much is it likely to cost?

A.: The most generic term is ammonium citrate, dibasic. Try using this chemical name when calling local chemical-supply houses. To get a price, we called Aldridge Chemical Co., Milwaukee, at 800-558-9160 and found that this supplier calls the product ammonium hydrogen citrate. You can buy 2.5 kilograms (about 5.5 pounds) of the prepackaged material from Aldridge for $83.55. If you buy more than 20 pounds in bulk, the price per pound is lower.

Since the recommended solution concentration is 2 pounds of diammonium citrate dissolved in a gallon of water, a gallon of solution costs about $30.