andy, that is covered in the directions: you start with between 1/2 and 1 lb of AA per 10,000 gallons and then add that much again if the stains aren't completely gone in 30 minutes. In cases of very severe metal stains you could end up using several pounds per 10,000 gallons (though that is quite rare).

Thanks, I ordered a 5lb bag from PC Networx Inc so we'll see how it goes. I'll start with 1lb per 10,000gal.