Tadpoles need calcium to thrive. Add liquid calcium, found in most pet stores, to the water every time you change it or add new water. The general rule of thumb is six drops per gallon of water, or two drops per liter. Do not feed tadpoles fish food, turtle food or any other meat-based food. Occasional small amounts of bloodworm can be given for a protein treat, but tadpoles require a vegetarian diet.