Product Details : Allow you to monitor the CO2 level in your tank from any angle. With smart design to prevent any chance of pill of the indicator solution. Reusable color chart sticker provides convenience in location change of the sticker. USAGE INSTRUCTIONS : Take apart the CO2 indicator. Add 1cc of indicator solution to the reservoir until the mid line, then reattach the top half of the CO2 indicator firmly. Submerge the CO2 indicator vertically and attach it to the desired location inside the tank by use of the suction cup. Stick the color chart on the glass wall of the tank ( the position to cover the suction cup) to read the CO2 level in your tank. Change solution every 2-4 weeks.