You might want to consider skipping the tablets and using the powdered Sodium Metabisulfite. It's a little cheaper, and easier to use for amounts of water that aren't in 5-gallon increments. I'm not near my bottle but, if recollection serves, I use 1/4 teaspoon per 5 gallons. I know that's not as accurate as weighing it out on a gram scale, but it's the closest approximation I can achieve without one.