With this cable you can plug into the APEX Dos DDr port and gain access to the optical sensors that the DDR would use. You can then hook 2 more optical sensors to your apex system. This cable will come with 2 opticals sensors. Optical are much better then float switches. You could also make your own dosing containers and put these optical sensors in them so you get a warning when your container is low. Comes with 2 optical sensors

Apex Dos DDR cable with 2 optical sensors