The pH electrode must be purchased separately (not included in the set). This CO2 fertiliser system features automatic CO2/pH control for the optimum supply of all aquarium plants in freshwater aquariums ranging from 40 to 600 liters. A factory-fresh pH electrode is required for operation. The assembly is simple: screw the pressure reducer onto the bottle, connect the solenoid valve to the CO2 controller, attach the hose to the bubble counter/check valve and the reactor, and connect the pH electrode. The CO2/pH controller measures the pH value (CO2-dependent) via the pH electrode and automatically regulates the CO2 supply through the solenoid valve until the ideal pH value is reached with the correct amount of CO2. The system includes a 500g reusable CO2 cylinder with a wall bracket, a pressure reducer with a solenoid valve, a CO2/pH computer, a 3m hose, a bubble counter with a check valve, a TAIFUN CO2 reactor with an extension set, 2x plant fertiliser (100ml each), and 1x daily fertiliser (10ml).