One of the most popular and inexpensive ways to descale your dishwasher is running a hot cycle with distilled white vinegar (the best for cleaning) and then a cycle with baking soda sprinkled along ...
To test baking soda, drop half a teaspoon into a small amount of vinegar. If it fizzes, it's still active. If you don't get any sort of reaction, it's time to toss that box and buy some new baking ...