RODI systems are essential for producing high-quality water for aquariums. However, using them without a TDS meter is like driving a car without a speedometer and gas gauge; you may end up in trouble. Monitoring TDS helps assess performance and filter quality. A dual TDS meter is recommended to check TDS readings in two places. One probe should be placed before the DI stage to show the RO's water quality, while the other should be placed after the DI stage to show how well the DI removes all remaining TDS from the final product water. This way, you can ensure your RODI system is functioning properly and producing water of high quality for your aquarium.