100% brand new and high quality Features: 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. A CO2 checker is an essential tool for monitoring CO2 levels in the aquarium. The CO2 checker is a reservoir designed to contain an indicator solution and an airspace. When the drop checker is submerged in the aquarium, the carbon dioxide will out-gas from the aquarium water into the airspace of the drop checker and will eventually be absorbed into the indicator solution. The carbon dioxide gas will seek a point of equilibrium between the indicator solution and the aquarium water. As equilibrium is achieved, the color of the indicator solution inside of the drop checker will change based on the concentration of CO2 in the aquarium water. Used for aquarium, fish tank How to use: 1.Will test agent about 15(or according to the actual amount) drops into the monitor, need not to add water 2.Change again every 30 days, airtight preservation at room temperature. Note: 1.Simply add couple drops of test solution and water into the checker. 2.Stick the checker on the edge of the aquarium. 3.Ensure water level cover the opening of the checker. 4.C02 indicator reagent not included! Specification: Material: Glass Height: app.5.5cm/2.17in Diameter: app.3cm/1.18in Color: Transparent Quantity: 1 Pc Note: 1.Please allow 1-3cm error due to manual measurement. pls make sure you do not mind before you bid. 2.Due to the difference between different monitors, the picture may not reflect the actual color of the item. Thank you! Package includes: 1 x Glass drop checker (with suction cup,C02 indicator reagent not included)