One reason why a detergent tablet may not dissolve completely during the wash cycle is simple placement. If the tablet is too close to the cover, it may end up sticking to the cover instead of dissolving. Set the tab flat inside the detergent cup, and then slide the lid over the dispenser until it clicks into place.
Other problems with the dispenser may cause the tablet to stick or clump as well, such as a damp dispenser cup. If the dispenser is wet, wipe it out with a dry cloth before placing the detergent inside. In addition, if there is already detergent residue in the cup, it may cause additional clumping or sticking. Clean it out with a damp sponge or cloth and then wipe dry before adding a new tablet.
Using hot water in a dishwasher is important as cold water generally cannot dissolve the soap as well or clean dishes as thoroughly. If the water temperature is below 120 degrees Fahrenheit, problems may result. Pour some hot water into a glass cup, and measure with a candy thermometer, and if the temperature is below 120 degrees, increase the setting at the home water heater.
Sometimes the reason that the soap does not dissolve is as simple as a dish that is blocking the water from entering the detergent dispenser. While large or tall items can be placed in the bottom rack for washing, set them along the sides and tilt them down instead of putting them in the front of the rack. Check the top rack for anything that might fall or hang and obstruct the dispenser as well.