Looks like I could skip the ascorbic acid and just use the citric acid.
Anyways 1.5 to 2 times more than a half to one pound of ascorbic acid per 10,000 gal seems excessive. According to the MSDS pdf for Metal Free, the product contains only 0.5 - 1.5 percent citric acid. And the instructions say to add 32oz (1L) of METALfree per 20,000 gallons. My calculator says .5% to 1.5% of 32 0z = .16 to .48 ounces of pure citric acid.
I am confused.