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Green Leaf Aquariums is a leading planted aquarium brand with 20 years industry expertise in: professional lifetime aquarium CO2 systems, the finest quality aquarium plant fertilizers, thriving aquarium plants & tissue cultures, and specializing in custom hardscape design

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  • Green Leaf Aquariums
  • Green Leaf Aquariums, LLC
    5200 NW 43RD STREET
    SUITE 102-264
    text/SMS:(833) 679-0910
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Cal Aqua Labs Double Check CO2 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

4 Reviews Hide Reviews Show Reviews

  • 5
    Simple, Elegant, Fool-proof

    Posted by David on 1st Apr 2021

    Both required solutions are premade and included. Took a little patience to fill the top chamber. I love that it eliminates the ambiguity factor. My only complaint is that it is a bit expensive for what it is. My only suggestion is to offer a model that uses magnets instead of a suction cup. Staff Reply: Thank you! The reason these are so expensive is because these are hand made. Think of them as one off art pieces. Literally no other brand or type even compares to quality or design. The magnet idea is really cool!

  • 5
    Wicked good

    Posted by Todd L Rhodes on 15th Nov 2019

    Very nice piece. Could only find this in the UK. Chuffed I could get it in the USA. This thing is perfect. Best part if it is the fact that within 30 mins it will already be showing you what your levels are. Others take 1 or 2 hours which can be misleading.

  • 5
    Nice co2 checker

    Posted by Melinda on 5th Oct 2019

    Works like is says, it does change color in response to co2 that's dissolved in the water. It's not hard to refill.

  • 4
    Beautiful piece.

    Posted by Erich on 27th Feb 2019

    The drop checker really is a piece of art. It seems to work well and looks great in the tank. Only reason I didn't give it 5 stars is the bend into the upper chamber is too narrow and makes it a frustrating chore to get the liquid in and out of it, let alone cleaning.

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