Measure and control alkalinity with the KH Director®. This device is designed to work with a GHL Doser 2 (2.1) Standalone (NOT INCLUDED) or a ProfiLux® Aquarium Controller 3 or 4 with a Doser 2 (2.1) Slave (NOT INCLUDED). Three dosing pumps are needed for it to function properly. If you do not have 3 unused pumps, consider buying the KHD/Doser 2.1 Set. *This item is for the KH Director ONLY.