Glass drop checker is by far the most reliable way to have a visual representation of your CO2 levels without all the guesswork. This is the simplest and most direct way. CO2 indicator solution needs to be used with the glass drop checker. When the solution is blue you need more CO2. If the color is yellow the CO2 is excessive if the color is green the amount of CO2 is suitableFeatures:THE PACKAGE INCLUDE: 15ML solution PH indicator. This needs to be used with the glass drop checker.GOOD CO2 DETECTION TOOL: Color change to determine how much CO2 needs to be added to the aquarium to help novices determine the right amount of CO2 dosage.3 COLOR DISPLAY: Long term monitor CO2 chroma the test solution color show: blue - insufficient CO2 green - sufficient CO2 yellow - excess CO2.ENSURE PLANT AND FISH SAFETY: Monitoring CO2 levels in your planted aquarium is very important for the health of your plants and fish.WORRY FREE WARRANTY: Any problem please contact our store without hesitation. Honor to serve youSpecification:Name: CO2 indicator solutionCapacity: 15MLPackage Information:Package size: 8.8*2.8*2.8cmPackage weight: 24gGift Box PackagingNote:There could be a few deviation due to manual measurement or slightly color difference as the result of shooting scene.Package List:1* 15ML CO2 indicator solution