How much electrolytes does your athlete need? Sodium is the one that counts — 3 to 4 grams a day at ages 10 to 18, and 2 to 3 grams at ages 6 to 9, spread across five blocks. Potassium, magnesium and calcium matter for health, but they are not what holds fluid in. Sweat carries roughly nine times more sodium than potassium. Food first, the salt shaker second, a product only where the schedule breaks