what's up Chuck,
Just go buy some powder-form oxalic acid. I buy it at a chem. plant here in Nashville for about $35 per 55# bag. I mix it about 24oz. to a bucket. I buy about 5 bags at a time, and spend some time filling 1gal. freezer bags with the appropriate amount. I have a couple Rubbermaid plastic boxes in my trailer and I fill them with these packages. That way, you don't have to do any measuring on the job. It also helps out with those employees that are having trouble grasping directions. Using straight oxalic acid does not do as good of a job as, say, Readyseal's brightener, but it is close enough. No need to buy pricey pre-mixed chems, just buy them in bags at your local chem. house.
jon