B.R.
Put about a cupful of baking soda into the wash. If you are a member of Sam's or Costco, you can buy baking soda in a large box or bag at a very low cost. I believe there is also a baking soda additive in the detergent aisle of most stores, but I don't think it would work any better than just the regular baking soda, and probably is more expensive.