This CO2 indicator allows you to monitor the CO2 levels in your tank from any angle. With a smart design to prevent any chance of spill from the indicator solution and a re-usable colour chart sticker. How to use: – Take apart the CO2 indicator – Add 1cc of indicator solution to the reservoir and then reattach the CO2 indicator firmly. – Submerse the CO2 indicator vertically and attach to the desired location in the tank by suction cup – Stick the colour chart on the glass wall of the tank to cover the suction cup to read CO2 levels in your tank. – Change solution every 2-4 weeks, solution change at water change is not necessary.