Features: 1. Glass drop checker with pre-mixed indicator solution, suction cup, and more 2. Dilution-free CO2 monitoring solution, no need to blend, 15ml large capacity, one bottle can be used 5-6 times. 3. To use simply fill the drop checker half way with the Co2 Indicator Solution. 4. Place suction cup on the drop checker and place in your planted tank. Wait 2 hours to read Co2 levels. 5. When your co2 is off the drop checker solution will be a deep blue color. After co2 has been on for around 2 hours you should notice the color change. Optimal co2 concentration will be at 30ppm which will be a green-light green color. If it remains blue your co2 is too low. If the color turns yellow then your levels are too high and may harm your fish. Specification: Material: glass Size: 4.6x4.2cm Notice: 1.Due to the different monitor and light effect, the actual color may be a slightly different from the picture color. 2.Please allow 1-3cm differs due to manual measurement. includes: Choice 1:1 x Aquarium CO2 Monitor includingSolution PH Indicator liquid) Choice 2: 1 x 15ml Solution PH Indicator (Liquid ONLY,CO2 Monitor NOT Included)