The Eshopps IV-300 Slave Unit will not operate without the Eshopps IV-200 Master Unit. You can upgrade the Eshopps IV-200 Dosing Pump Master Unit by adding an Eshopps IV-300 Dosing Pump Slave Unit (sold separately).
One master unit can control two slave units giving you up to eight independently controllable dosing channels. When dosing liquids to your aquarium each successive pump activates in 5-minute intervals when pump channels are set to dose at the same time. This prevents different additives from interfering with each other.