Double Check CO2 Checker

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Cal Aqua Labs' "Double Check" series is the only 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. The top chamber holds the CO2 indicator solution, whereas the bottom chamber carries a CO2 reference solution. The reference solution color corresponds to 30 ppm of CO2 - a level that is widely accepted for good plant growth in most aquariums.

No more guessing on the shades of green. No more looking back-and-forth at color sheets to compare. You know the precise CO2 level simply by comparing the colors in the two compartments side-by-side. Don't guess, be sure! It's as simple as that.


  • Unique dual-compartment design. Top compartment holds the Indicator solution, while the bottom compartment holds the Reference solution
  • No solution preparation needed. Required solutions are premade and included
  • Improved durability and ease of use
  • Easy to fill and remove solutions from both chambers
  • Simple to use, simple to read, higher accuracy than other single-compartment checkers

Each set includes:

  • 1 Double-Check 2 CO2 checker
  • 1 x 15ml Reference solution, calibrated to 30ppm CO2
  • 1 x 15ml Indicator solution
  • 1 suction cup
  • 2 Reference chamber plugs
  • Use instructions

Approximate size without suction cup: 2"x1.5" (HxW)