Cal Aqua Labs

Cal Aqua Labs Double Check Drop 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, the bottom chamber holds 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.

This innovative drop checker is designed to be efficient and accurate, implementing a simple visual comparison of the CO2 level in one's aquarium with an optimal CO2 level, indicated by the standard reference solution. The Double Check drop checker eliminates the guesswork normally involved in determining which shade of green is considered optimal, and reduces the need for color comparison references. The precise and prime CO2 level is achieved when the colors in the two compartments are identical.

The Double Check is hand-crafted using only the highest quality, laboratory-grade, borosilicate glass for maximum strength, durability, and visual clarity. Each piece is unique.

  • Top Compartment - "Indicator" solution
  • Bottom Compartment - "Reference" solution
  • No solution preparation required. 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
  • Approximate size without suction cup: 2"x1.5" (HxW)


  • One (1) Suction Cup
  • One (1) Bottle of CO2 "Indicator" Solution (15 mL)
  • One (1) Bottle of CO2 "Reference" Solution calibrated to 30ppm CO2 (15 mL)
  • 2 Reference chamber plugs
  • Instructions for use

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