Dr.Mj Coco: "Doses are very small! I use 1/8 tsp per 5 gallons. I recommend measuring 1/8 tsp and dividing it into 5 piles. Once you get this sense of how much you need you can just eyeball a pinch. The dose doesn't have to be super precise, but it should be reasonably close."
Test EC first - if it's too high, lower it by slowly adding purified water that's had a normal dose of CalMag added to it. THEN measure the PH - keep it in the higher range if possible. Don't trust the PH meter, use the strips.