Direct Info from Product Website : https://www.co2art.eu/products/aquarium-co2-drop-checker-set

Specially-designed to suit a professional’s needs.

Made of glass, for max reliability.

Supplied with 15ml Drop Checker Solution and Suction Cup

No mixing nor preparation required.

This is everything that you need to start monitoring CO2 levels in your aquarium.

Drop Checker is an original glassware product, designed to indicate the CO2 amount diluted within the aquarium water with color change of the pH reagent inside, in order to understand the proper amount of CO2 supply.

Drop Checker Size:

Outside diameter:3cm
Height:5.5cm