If your dishwasher detergent already includes rinse aid, you do not need to add an additional rinse aid separately. Dishwasher detergents that include rinse aid are designed to provide a complete cleaning and drying solution for your dishes.
Rinse aid is a chemical additive that helps improve the drying process by reducing water spots and promoting faster evaporation of water from the dishes. It also helps prevent water from forming droplets on the dishes, which can lead to spots and streaks during the drying cycle.
When using a dishwasher detergent with built-in rinse aid, follow the manufacturer's instructions for the correct amount of detergent to use in each wash cycle. Using the detergent as directed should provide you with clean and dry dishes without the need for additional rinse aid.
However, if you find that your dishes are not drying as well as you'd like or if you notice water spots and streaks, you can experiment with adjusting the amount of detergent used or try a different brand of detergent to see if it improves the results.