CO2 Checkers

Maintaining the appropriate CO2 level is critical in a planted aquarium. Too much CO2 may harm your fish, whereas too little CO2 decreases plant growth and allows algae to take over. Cal Aqua Labs’ CO2 checkers allow you to monitor the CO2 level inside your aquarium. Handmade from the highest quality borosilicate glass, the CO2 checkers are an elegant addition to your planted aquarium.

PEARL CO2 Checker

Product code: 11004

Cal Aqua Labs’ PEARL is the first dual-compartment CO2 checker that places the reference chamber right inside the indicator chamber. This results in an elegant, space-saving design that allows for a close and accurate color comparison.


CLIP CO2 Checker

Product code: 12007

Cal Aqua Labs’ CLIP is the first CO2 checker that can be mounted on either the left, right, or the back side of the aquarium. It can even be hung on the rim of rimless tanks! This allows greater flexibility in the device’s placement within the aquarium. Perfect for nano tanks


CLIP nano CO2 Checker

Product code: 12008

Cal Aqua Labs’ CLIP nano is the CLIP CO2 checker designed without the suction cup stub. It is suitable for hanging on rimless aquariums 20 gallons (60 cm) or smaller, giving a clean, elegant look. Perfect for nano tanks.



Product code: 11001

Cal Aqua Labs’ DOUBLE CHECK 2 is the first all-glass dual-compartment CO2 checker that allows the user to accurately compare the CO2 level in your aquarium side-by-side against a standard reference.


ORACLE CO2 Checker

Product code: 12001

Cal Aqua Labs’ ORACLE combines the elegance of a glass CO2 checker with a white background inside the solution chamber for increased contrast and easy reading.


NANO CO2 Checker

Product code: 12006

Cal Aqua Labs’ NANO is designed specially for small aquariums. Measuring approximately 3 cm x 3 cm, it is small enough to appear unobtrusive yet large enough to provide a clear and accurate reading


CO2 Checker Accessories

60 ml Indicator Refill Solution

Product code: 11002

60 ml. Indicator refill solution for use with CAL AQUA LABS’s CO2 checkers. It consists of a premade 4dKH solution containing the appropriate amount of indicator.  Easy to use, no mixing required. Simply open cap and fill CO2 checker.  It is also more accurate than starting off with a regular 4dKH solution and adding drops of indicator separately.  This is because the additional liquid contained in the indicator drops will further dilute your 4 dKH solution, resulting in a final solution that is less than 4 dKH.

60 ml Reference Refill Solution

Product code: 11003

60 ml. Reference refill solution for use with CAL AQUA LABS’s dual chamber CO2 checkers. The reference solution is calibrated to 30 ppm CO2. Easy to use, no mixing required. Simply open cap and fill CO2 checker.