Cal Aqua Lab’s newest innovation, the Pearl CO2 drop checker. The ‘Pearl’ is a dual compartment CO2 checker that allows the user to accurately compare the CO2 level in your aquarium side-by-side against a standard reference. The unique space-saving design places the reference chamber right inside the indicator chamber. The inner chamber holds the CO2 reference solution, the outer chamber carries a CO2 indicator solution. The reference solution color corresponds to 30 ppm of CO2.