Blister pack for the JBL PROAQUATEST CO2 Direct refill, two titration reagent bottles

Reagent refill for dissolved CO2 test

Name: Reagent refill for dissolved CO2 test
Brand: Hardy Dewerse
SKU: J2414100
Price: 7.9 EUR
Availability: InStock

7,90 €

2,63 € × 3 with no fees Klarna.

These two bottles are the reagents for the dissolved CO2 test. They are used to measure the free carbon dioxide in your water, not the carbonates measured by carbonate hardness.

The reading is taken by titration: each drop of the second reagent equals 2 mg/L, and the final pink colour must hold for 60 seconds. The test tube and the two-field colour chart from your kit remain in use.

Ref. J2414100·Reagent refill

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The summary

What it measures: free carbon dioxide, not the carbonates that make up hardness.
What's in the box: 2 bottles of titration reagents.
How to read the result: count the drops, each one representing 2 mg/L.
What to aim for: 15 to 30 mg/L, with the ideal range for plants between 20 and 25.

The two titration reagents on their own, one drop equals 2 mg/L of CO2

Dissolved carbon dioxide is the free CO2 in your water, which plants use for photosynthesis. It is not the same as the carbonates you measure via carbonate hardness. These two bottles are the titration reagents alone for the direct CO2 test, for fresh water.

🫧 One drop equals 2 mg/L

Draw 20 ml of water into the syringe, making sure there are no bubbles, and place the test tube on the white section of the colour chart. Add 5 drops of reagent 1, then add reagent 2 drop by drop, swirling after each drop, until a pink colour remains stable for 60 seconds and matches the pink section of the chart. The number of drops multiplied by 2 gives the concentration in mg/L, so 10 drops corresponds to 20 mg/L of CO2.

The blank value

Aerate 100 ml of the same water for 15 minutes, measure it, then subtract that result from your reading.

The pink that holds

A pink colour that fades back to colourless before 60 seconds means the titration is not complete.

An air pump for the blank value reading

The blank reading requires aerating 100 ml of water for 15 minutes using a pump and a diffuser. A single- or twin-outlet aquarium air pump is sufficient for this sample, and it can also be used to aerate your tank if the CO2 level exceeds the recommended range. Without this correction, other acids present in the water add a few milligrams to each reading.

A highly flammable reagent inside the box

Reagent 1 carries the H225 hazard statement, indicating a highly flammable liquid and vapour, and Reagent 2 causes severe skin burns and eye damage. Store the kit in a dry place at room temperature, away from any naked flame, heat source or lighting rail, and rinse thoroughly with water if any splashes into your eyes.

🍃 The plants' equilibrium point

In your tank, a level of 15 to 30 mg/L is safe for fish whilst ensuring good plant growth, with the ideal sitting between 20 and 25 mg/L, and some heavily planted tanks reaching up to 35 mg/L. This test is primarily used to calibrate a CO2 injection system, such as a pressurised CO2 kit. It does not monitor a so-called liquid carbon fertiliser, which contains no CO2. The pH depends on both this level and the carbonate hardness, and the guide on regulating pH explains this relationship.

🧪 Two titration bottles

With a titration test, the number of measurements per bottle depends on your water: water with a high gas content requires more drops of reagent 2, and the blank value doubles with every check. The reagent 2 bottle therefore empties faster than the first, and its level is what tells you when to restock. Keep the bottles upright, tip facing down and dry on the outside, then store them sealed in their original packaging.

Technical specifications

What the refill contains

Contents: 2 reagent bottlesReagents 1 and 2, with child-safety caps
Manufacturer's reference: JBL 2414100, PROAQUATEST rangeNot to be confused with 2414000, which is the complete kit

Counting the drops

No reading: 1 drop = 2 mg/L10 drops of reagent 2 therefore correspond to 20 mg/L of CO2
Water volume: 20 ml, bubble-freeDrawn up slowly with a syringe. A bubble carries off gas and brings the reading down

Reference points and safety

Target values: 15 to 30 mg/LThe ideal range is between 20 and 25 mg/L, up to 35 in a heavily planted tank. Freshwater only
Hazard classification: Warning, the 2 bottlesH225 and H319 on reagent 1, H314 and H318 on reagent 2

To budget for separately

Test tube and colour chart: Those from the CO2 testThe test tube takes 20 ml, and the colour chart has two panels, one white and one pink
Air pump and diffuser: For the blank value100 ml of the same water, aerated for 15 minutes before the reference measurement

In the box

2 reagent bottles with child-resistant caps

Reference, EAN code, contents, protocol, number of measurements, and hazard statements taken from the JBL data sheet and instructions on 07/10/2026. The benchmarks of 15 to 30 mg/L and the blank value come from the JBL instructions. With a titration, the number of measurements per bottle depends on the value being measured.

Estimate your
delivery time

0.08 kg parcel, dispatched within 48 hours by Colissimo or Chronopost home delivery, your choice at checkout. The two bottles are sent in their original packaging. The exact shipping cost is shown in the basket.

Frequently asked questions

6 questions

6 key questions

Does this test measure carbonate hardness?

Why collect the 20 ml sample without any bubbles?

What is the purpose of the blank value on aerated water?

Draw off 100 ml of your water into an open container.
Aerate it for 15 minutes with an air pump and a diffuser, long enough for it to lose its free carbon dioxide.
Take a normal reading from this aerated water.
Subtract this result from the reading taken from the tank water.

This blank measures what the protocol counts over and above the gas actually dissolved. Without it, you will consistently read a few milligrams too high.

Why must the pink colour hold for 60 seconds?

Does this test measure a liquid carbon fertiliser?

One reagent is highly flammable — where should you store the box?

Reagent 1 carries the H225 hazard statement — highly flammable liquid and vapour — as well as H319. This is the point that governs storage.

Keep the box up high, dry, at room temperature, and away from any flame or heat source — not on top of a lighting unit and not near a heater.

Reagent 2 carries the H314 and H318 statements, for severe burns and eye damage: rinse the eye thoroughly for a prolonged period if splashing occurs. Empty bottles should be taken to a recycling centre with other household chemicals.

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Reagent refill for dissolved CO2 test

The summary