JBL ProAquaTest KH Carbonate Hardness RefillSimple and safe control of water parameters in aquariums and ponds. Determination of the optimal carbonate hardness for freshwater and seawater.Color test: fill the plastic test tube with water to be tested, add reagent dropwise until the color changes from blue to yellow. Use: When using water for the first time: once a day for the first week, then once a week.On the JBL website/Topics/Aquarium or Pond, you will find detailed information on water analysis and troubleshootingContents: 1 Quick KH Test, 1 reagent, plastic test tube. Reagent refills available separately.