Sodium Bi-sulfate is what jewelry makers use to clean scale off metal. I just did an experiment. 1 gallon of White Vinegar was $2.99 at the supermarket. I mixed it with tap water 50/50. The tap water was 7 PH before I mixed. After mixing, it was 4.3 PH. So it seems like we need about 4 PH. So, that mix is $1.50 per gallon. I then went to Leslie's Pool Supply and bought 10 lbs of 'dry acid' (93% Sodium Bi-Sulfate). With tax it costs $25.49. I tried various amounts per 100 ml of water (in a graduated cylinder). I started with 21 grains, and the PH was under 3.5. I did it over and over, and in the end, found that 0.4 grains per 100 ml was 4 PH. So that means, we need 15 grains of powder per gallon to match the Vinegar mix. So 10 lbs makes 4667 gallons. $25.49/4667 = 0.55 cents per gallon (1/2 penny). So Vinegar mix is 271 times more expensive than this solution.