A dishwasher is intended to make housework easier, but when it doesn't work properly it can result in even more work than washing dishes by hand. Dishwasher detergent that doesn't dissolve can leave the dishes dirty and get stuck all over the inside of the machine. Detergent might not dissolve for several reasons, such as water temperature and how the detergent is stored.
Powdered dishwasher detergent dissolves much better in hot water than in cool or warm water. If the water is not hot as it enters the dishwasher, or if the heating element is not working well, the water may not be hot enough to dissolve the detergent completely. Run the water in the kitchen sink until it is hot before starting the dishwasher. Have a professional test the heating element to see if it is working properly if the water is still not hot enough.
If the detergent cup is not opening at the right time during the wash cycle, the detergent may not be released when there is enough water in the dishwasher to dissolve it completely. The cover may also not be opening completely, keeping part of the detergent inside for the entire cycle or for too long during the cycle. Check around the cover and its hinge for build-up, debris or anything that would block it from opening normally. Use white vinegar to clean the cover and the hinge.
Dishwasher detergent absorbs moisture quickly. If it absorbs too much moisture, it will begin to clump together. Those clumps can harden and make it difficult for the detergent to dissolve during the wash cycle. Even if the detergent does not clump, it can also become more difficult to dissolve because the granules have hardened from the excess moisture absorption. Keep the lid tightly closed. Store the detergent in a cool, dry place.
Hard water does not dissolve dishwasher detergent as readily as soft water. If the water is too hard, it may not dissolve all of the detergent. A water softening system can solve this problem, but can be expensive. Another option is to increase the water temperature through the water heater. Also, fill both detergent cups, rather than just one to give some extra cleaning power.