Box for the CO2 drop water test, water analysis range, cardboard format for freshwater aquariums

Contents of the CO2 water test: two reagent bottles, graduated test tubes, sampling syringe and two-box colour chart

Two reading scales for dissolved CO2 in mg per litre: the manufacturer's scale for plants and the aquaculture literature scale for fish.

Curves of dissolved CO2 and pH over twenty-four hours in a planted tank, moving in opposite directions between day and night.

Dissolved CO2 water test in drops, direct measurement

Name: Dissolved CO2 water test in drops, direct measurement
Brand: JBL
Price: 1700.0 RSD
Availability: InStock

1,700.00 RSD

566.66 RSD × 3 with no fees Klarna.

Dissolved CO2 feeds your plants, but in excess it interferes with your fish's ability to breathe. This test gives you the result directly in mg/L: count the drops of the second reagent until the colour shifts to pink, and each drop represents 2 mg/L.

The alternative method, the table that cross-references pH and KH, assumes that the acidity of your water comes from carbon dioxide. A titration makes no such assumption.

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The summary

What you are measuring: the carbon dioxide actually dissolved, read directly in mg/L, without going through pH or KH.
What you receive: 2 bottles of reagents, a plastic test tube graduated up to 20 ml and a two-box colour chart.
What the figure means: aim for 15 to 30 mg/L, a range that is safe for your fish, and 20 to 25 mg/L for optimal growth.
Duration: 3 minutes, with no waiting time, since the colour is judged drop by drop.
How to choose: the two test kits deduce the CO2 from a table, whereas this test measures it in the water.
Two classified reagents: the first highly flammable, the second corrosive; the titration is carried out in the test tube, and they never go into the fish's water.

Drop titration test, 1 drop = 2 mg/L of CO2, for freshwater

This test measures dissolved carbon dioxide in freshwater by titration: each drop of the second reagent equals 2 mg/L, with no need for the pH or the KH. Between 15 and 30 mg/L, the water remains safe for fish. The two reagents, one highly flammable and the other corrosive, never go into the fish water.

Dissolved carbon dioxide is the primary nutrient for aquatic plants, and it is also a gas that, in excess, stops fish from expelling the CO2 produced by their own respiration. The range that suits both plants and fish is narrow, so it is best set from a measured figure rather than by eye.

📊 The pH and KH table

The most common method is indirect: you measure the pH, you measure the KH with a carbonate hardness test, you cross-reference the two on a chart and you read off the CO2. It rests on an assumption that is rarely spelled out, namely that all the acidity in your water comes from carbon dioxide. Add peat, catappa leaves, wood that releases its tannins or a commercial acidifier, and other acid-base pairs enter the calculation. Titration, by contrast, measures the carbonic acid actually present in the sample, and the blank value subtracts the share due to other acids.

Subtract the blank value from each measurement

Acids other than carbon dioxide can use up reagent and skew the titration. So aerate 100 ml of your water for 15 minutes with an air pump and a diffuser, do a complete measurement on this water, then subtract this result from your actual measurement. Without this subtraction, your figure is too high by the full blank value.

Amber water or peat-filtered water

The table shows a high CO2 level that the water does not actually contain, which leads you to wrongly reduce an injection that the plants need.

After a shop-bought acidifier

It lowers the pH without changing the carbon dioxide content, so the calculated value rises while the actual content stays the same.

Clear, mineral-rich water

The table and the titration agree. This is the case where the indirect method is legitimate.

In aquaponics

The foliage of your crops develops out of the water and takes its carbon from the air. The test is used here mainly to check that the CO2 given off by the fish does not build up.

🐟 Too much CO2 in fish

An excess of carbon dioxide does not change the appearance of the water, but it can be recognised by the behaviour of the fish: they come to the surface, open their gill covers wide and slow down, exactly as if they were short of oxygen, even though the water may contain enough. When CO2 builds up, the fish can no longer expel its own through the gills and its blood becomes acidic. Vigorous aeration drives off this excess CO2, and the dissolved oxygen test lets you decide between the two diagnoses.

Have the refill ready while adjusting an injection

Every serious check requires two titrations, one for your water and one for the blank value, so reagent 2 is used up faster than you might expect. If you are adjusting a gas injection, order the reagent refill together with the test. You will then be able to take the morning and evening readings throughout the whole adjustment period, without interrupting the series just as the flow rate stabilises.

🌗 Two readings a day

In a planted tank, the CO2 level falls during the lighting period, because photosynthesis consumes it, and rises at night, when plants and bacteria release it without taking any up. Two readings on the same day, in the morning before the lights come on and in the late afternoon, therefore tell you far more than a weekly measurement taken at a random hour, and they explain the late-night fish losses seen in overdosed tanks. If you want the injection to follow this curve by itself, the CO2 controller opens and closes the solenoid valve according to the continuously measured pH, and this test is then used to check the actual level.

🥽 Ethanol and a corrosive reagent

The first reagent contains more than 50% ethanol: it is highly flammable and irritates the eyes. The second is classed as corrosive to the skin and eyes. The titration is done drop by drop in the test tube filled to 20 ml, shaking after each drop, so over a sink, away from any flame, heat lamp or cigarette. Once the pink colour change is reached, the sample goes down the sink; poured into a planted tank or an aquaponic system, it would introduce alcohol and a corrosive reagent to the fish and the roots alike. While you are adjusting an injection, when you measure morning and evening, the CO2 reagent refill saves you from running out of a bottle mid-week.

Technical specifications

Measuring CO2

Parameter measured: Dissolved CO2, in mg/LThe free carbon dioxide in the water, not the carbonates that carbonate hardness counts
Method: Titration, you count the dropsNo colour to compare against a scale: stop at the pink turn, which must hold for 60 seconds
No reading: 1 drop = 2 mg/LSo, 10 drops of reagent 2 correspond to 20 mg/L of CO2
Target values: 15 to 30 mg/LHarmless to fish. The target range for plants is 20 to 25 mg/L, up to 35 mg/L in a heavily planted tank
Shaded surroundings: Freshwater onlyThis test does not check fertilisers known as liquid carbon
Manufacturer's reference: JBL 2414000, PROAQUATEST rangeEAN code 4014162241405

The procedure

Water volume: 20 ml, no bubblesPoured down the side of the tube. A bubble carries off carbon dioxide and lowers the result
The steps: Rinse, fill, place, dose, titrate, countIn this order: 5 drops of reagent 1, then reagent 2 drop by drop until the colour changes
Waiting time: NoneJudge the colour drop by drop; only the final pink must hold for 60 seconds
Total time: About 3 minutesApart from the blank value, which requires 15 minutes of aeration
Reading: Seen from above, pink square on the colour chartThe test tube is viewed from above, over the white square and the pink square
Correction required: Blank reading on aerated waterAerate 100 ml for 15 minutes, measure, and subtract that result from your reading

Hazard labelling

Signal word: DangerOn both bottles
Pictograms: Flame, exclamation mark, corrosionGHS02 and GHS07 for reagent 1, GHS05 for reagent 2
Hazard statements: H225, H319, H314Highly flammable liquid and eye irritation (ethanol in reagent 1), burns to skin and eyes (reagent 2)
Precautionary statements: P101, P102, P303+P361+P353, P305+P351+P338, P501Label for the doctor, keep away from children, rinse skin and eyes, dispose of in accordance with regulations
Precautions: Sink, ventilated room, out of reachReagent 1 to be kept away from any flame, child-resistant caps
Titrated sample: Poured down the sinkNever put back in the tank or the system

To allow for in addition

A 20 ml syringe: For drawing a sample without bubblesThe protocol calls for 20 ml drawn off without any air bubbles
Reagent refills: Reagents only, ref. 2414100The test tube and colour chart can be kept

12 further specifications are available in the detailed view.

In the box

2 reagent bottles, closed with child-resistant safety caps
1 plastic test tube graduated up to 20 ml
1 colour chart with 2 squares, one white and one pink
1 multilingual instruction leaflet, French included

Manufacturer's values (instructions for use, colour chart and safety data sheets for the two reagents).

Manufacturer and product safety

Manufacturer: JBL GmbH & Co. KG
Postal address: Dieselstraße 3, 67141 Neuhofen, Allemagne
Contact: info@jbl.de
Website: www.jbl.de

Information provided under Regulation (EU) 2023/988 on general product safety.

Measure the CO2, or work it out?

Both test cases count CO2 among their parameters, but they work it out from a table using pH and KH. This test measures it in the water. It is not the same information, and the two diverge as soon as the water is tannic or acidified.

The pH-KH chart becomes inaccurate in tannin-rich water It assumes that all the acidity comes from CO2. As soon as roots, peat or an acidifier come into play, it indicates CO2 that the water does not contain, whereas titration measures the dissolved gas directly.

	CO2 measured in the water, by titration	CO2 worked out from a pH and KH table	Still valid on tannin-rich or acidified water	Parameters covered	Drop test kits included	pH, KH, nitrite and nitrate	GH, iron, phosphates, copper, silicates, oxygen	Reagent bottles (bottles)	Glass test tubes	Laboratory comparator block	Thermometer	Reagent refill sold separately	Price
Recommended CO2 test on its own, direct measurementYour choice	Yes	No	Yes	1	1	No	No	2 bottles	0	No	No	Yes	1,700.00 RSD
6-in-1 Aquarium Water Testing KitYour choice	No	Yes	No	6	5	Yes	No	9 bottles	3	Yes	No	Yes	6,200.00 RSD
JBL ProAquaTest Lab water analysis case, 13 tests for aquarium and pondYour choice	No	Yes	No	12	13	Yes	Yes	23 bottles	12	Yes	Yes	Yes	12,000.00 RSD

CO2 test on its own, direct measurementRecommended

How the CO2 is produced

CO2 measured in the water, by titrationYes

CO2 worked out from a pH and KH tableNo

Still valid on tannin-rich or acidified waterYes

What you are measuring

Parameters covered1

Drop test kits included1

pH, KH, nitrite and nitrateNo

GH, iron, phosphates, copper, silicates, oxygenNo

Equipment supplied

Reagent bottles (bottles)2 bottles

Glass test tubes0

Laboratory comparator blockNo

ThermometerNo

Budget

Reagent refill sold separatelyYes

6-in-1 Aquarium Water Testing Kit

How the CO2 is produced

CO2 measured in the water, by titrationNo

CO2 worked out from a pH and KH tableYes

Still valid on tannin-rich or acidified waterNo

What you are measuring

Parameters covered6

Drop test kits included5

pH, KH, nitrite and nitrateYes

GH, iron, phosphates, copper, silicates, oxygenNo

Equipment supplied

Reagent bottles (bottles)9 bottles

Glass test tubes3

Laboratory comparator blockYes

ThermometerNo

Budget

Reagent refill sold separatelyYes

JBL ProAquaTest Lab water analysis case, 13 tests for aquarium and pond

How the CO2 is produced

CO2 measured in the water, by titrationNo

CO2 worked out from a pH and KH tableYes

Still valid on tannin-rich or acidified waterNo

What you are measuring

Parameters covered12

Drop test kits included13

pH, KH, nitrite and nitrateYes

GH, iron, phosphates, copper, silicates, oxygenYes

Equipment supplied

Reagent bottles (bottles)23 bottles

Glass test tubes12

Laboratory comparator blockYes

ThermometerYes

Budget

Reagent refill sold separatelyYes

Parameters and equipment of the two kits taken from their data sheets; both work out CO2 from a table.

Documents & manuals

Official manufacturer's instructions, in French

Full titration protocol, 20 ml reference volume, stable pink endpoint rule of 60 seconds, and blank value determination.

PDF · 1,6 Mo

Download

Estimate your
delivery time

Parcel of 0.13 kg, dispatched within 48 h by Colissimo or Chronopost to your home, as you choose during payment. The reagents are sent in their original box, with dropper caps screwed on. The exact amount is shown in your basket. Once unsealed, this product can no longer be returned under the right of withdrawal (article L221-28, 5° of the French Consumer Code), for reasons of hygiene and health protection.

Frequently asked questions

6 questions

6 key questions

Too much CO2, how can you tell from the fish?

They come up to breathe at the surface, open their gill covers wide and become sluggish, exactly as if they were short of oxygen. Vigorous aeration deals with both cases at once, since by agitating the surface it drives off the excess CO2 while also adding oxygen. Afterwards, measure the CO2 and the oxygen to find out which one was responsible, and reduce the injection if it was the gas.

What level should you aim for in a planted aquarium?

Does this test replace the pH and KH chart?

Do you really need to run the blank value?

Take 100 ml of your water and aerate it for 15 minutes.
Run a full test on this aerated water and note the number of drops.
Run your actual test on 20 ml of water from the tank.
Subtract the first result from the second.

Aerated water contains almost no CO2: whatever reagent it still uses up measures everything in your water that is not carbon dioxide. Without this subtraction, your figure will always read too high.

My permanent indicator and this test give different readings. Which should I trust?

Do I need this test if I don't inject CO2?

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Dissolved CO2 water test in drops, direct measurement

The summary