Description: Maintaining proper Carbon Dioxide (CO2) levels in the planted aquarium is one of the most important factors in the health of the planted aquarium ecosystem. The use of Drop Checker is recommended as it makes it easy to figure out the CO2 level in an anqurium Long term monitor Co2 the color show :Blue - insufficient Co2,Green - sufficient Co2,Yellow - excess Co2 Best use in anqurium Material: Glass Specification: Material: Glass Diameter: Approx.2.5cm/0.98inch Size(L x W): Approx. 4.5x5cm/1.77x1.97inch Instructions: 1. Turn drop checker up-side-down and place 3 drops of test solution into the drop checker. 2. Use a pipette (not include) to inject tank water into the drop checker. You will see the color change on the solution according to Co2 content in the tank water. 3. Turn drop checker up-side-down again carefully, and place the drop checker inside the tank below water level. Package Includes: 1 Piece Drop Checker 1 Piece Suction Cups Note: Since the size above is measured by hand, the size of the actual item could be slightly different from the size above. Due to the lighting effects, monitor settings, etc. There could be some slight difference in the color of the pictures and the actual item.Customer satisfaction is our primary concern. If the product is somehow cracked or broken during shipping, please feel free to contact us. We will try our best to give you a satisfactory solution.