You need to add 1.67 grams of Sodium Tetraborate Decahydrate (10 Mule Team Borax) to 1 gallon of water to produce 50 ppm. So with your accuracy of +/- 1 gram, you could add 17 grams to 10 gallons of water and be pretty close to 50 ppm.

The trick in the calculations isn't the 381 g/mole of the Borax, but the fact that the ppm of Borates on the test strip is in ppm of Boron at 10.8 g/mole. It took Evan and I a while to figure that one out.

Richard