With its long-lasting usage, one bottle of the CO2 testing solution can be used multiple times, providing you with a cost-effective solution. You can this product to accurately measure the CO2 concentration in your aquarium for an extended period, without the need for frequent replacements. Features -Color:Multi -Material:methyl blue -Size:7.70X2.10X2.10cm/3.03X0.83X0.83in -Note: 15ml, no need to mix with tank water; Green: right balance of CO2; yellow: too much CO2; blue: too little CO2 -Ensure a healthy ecological environment with precise monitoring of carbon dioxide -Our co2 detection liquid provides precise readings to help you make informed decisions about your aquatic environment. -With just a small amount of liquid, you can monitor your aquarium's co2 levels for an extended period of time. -Whether you're a hobbyist or a professional, our co2 detection solution can help you maintain a healthy and thriving aquatic environment. -Just add of the liquid to your aquarium water and wait for the color change to indicate the co2 level. Package list: 1 x bottle of indicator solution