Box for the KH carbonate hardness water test, 10.6 by 17.5 cm, reagent and test tube inside

Front view of the KH carbonate hardness test box on a white background

Contents of the KH carbonate hardness test: the reagent bottle and the graduated plastic test tube from 5 to 20 ml

Carbonate hardness measurement in progress: the reagent being added drop by drop to the test tube held by hand

Carbonates hardness test reading chart: one drop equals 1 degree KH, recommended ranges from 3 to 20 degrees depending on the tank, and alkalinity consumed by nitrification

KH carbonate hardness water test in drops

Name: KH carbonate hardness water test in drops
Brand: JBL
Price: 1800.0 JPY
Availability: InStock

¥1,800

¥600 × 3 with no fees Klarna.

Carbonate hardness is the buffering capacity of your water — its ability to neutralise acidification without the pH fluctuating. This test measures it in aquariums, ponds, and aquaponics systems.

The measurement is done by titration: you count the drops until the colour changes from blue to orange-yellow, and each drop equals 1 °dKH.

Water test

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The summary

What you receive: 1 bottle of KH reagent, 1 graduated plastic test tube from 5 to 20 ml, and the multilingual instruction leaflet.
What you measure: the carbonates that stabilise your pH, in fresh water, ponds, salt water, and aquaponics.
How to read the result: by titration — one drop equals 1 °dKH. No colour chart, no shade to interpret, simply count the drops.
How long it takes: 2 minutes, with no waiting time. The colour change is immediate.
How to choose: this test should always be used alongside a pH test, never on its own.
What gets sent to you: a parcel of 0,09 kg, reagent in its original box.

Drop titration test, one drop equals 1 °dKH, for aquariums, ponds and aquaponics

Carbonate hardness, written as KH, measures dissolved carbonates and bicarbonates, in other words, the buffering capacity of the water: these compounds neutralise the acids produced in the tank and keep the pH stable. A pH that fluctuates noticeably from one day to the next is almost always a sign of KH that is too low, because once these carbonates are exhausted, every acid input causes the pH to drop with nothing to cushion it.

🧱 The 5 °dKH floor

Carbonate hardness should not drop below 5 °dKH, whether in a garden pond or a tank where you inject CO2, and most freshwater fish and plants thrive between 5 and 16 °dKH. Below that level, there are no longer enough carbonates to buffer the acids continuously produced by your fish's respiration and by nitrification, and the pH can crash sharply overnight. A sudden drop like that is far more dangerous for fish than a persistently incorrect pH, which is why you measure KH at the same time as pH, never separately.

🌿 KH in aquaponics

Nitrification is an acidifying reaction: the bacteria that convert ammonium into nitrites and then into nitrates release protons, which are neutralised by the alkalinity of your water. Nitrifying 1 mg/L of ammoniacal nitrogen consumes approximately 0.4 °dKH, meaning that a system converting 5 mg/L of nitrogen loses around 2 °dKH. Your system therefore loses alkalinity week after week, with nothing to replenish it if your top-up water is soft. Potassium bicarbonate raises the KH while simultaneously supplying potassium to your crops.

Low KH, low and unstable pH

This is the most common situation: raise the KH first, and the pH will then stabilise on its own.

Low KH, high pH

This pH is unbuffered, so the first acidification will cause it to drop sharply.

High KH, pH difficult to lower

The buffering capacity neutralises the acidifier as you add it: first reduce the KH by diluting the water with RO water.

A limestone rock

It barely dissolves above pH 7, which is why it raises the KH so little.

The two things that drain your KH

Switching from tap water to RO water or rainwater reduces the KH in proportion to the blend, and this drop often goes unnoticed until the pH crashes. A technical soil for planted tanks also locks up carbonates, lowering the KH for several months, which often leads to the test being wrongly suspected of being faulty.

Measure the GH separately for mineral levels in living systems

KH measures carbonates, and therefore buffering capacity, but not calcium or magnesium. If you keep shrimps or snails, or if your plants show a magnesium deficiency, also use the total hardness test: it measures calcium and magnesium, the minerals on which fish, shrimps, and plants depend. The two values have no fixed relationship, so this second figure helps you avoid correcting the wrong parameter.

☀️ Biogenic decalcification

When carbon dioxide runs short, aquatic plants and particularly algae, which take it up very rapidly through photosynthesis, draw carbon from the bicarbonates dissolved in the water. This phenomenon, known as biogenic decalcification, lowers the carbonate hardness and causes pH to rise to levels that are dangerous for fish, most often towards the end of a sunny day in an algae-laden pond. A KH that drops without any addition of osmotic water or rainfall, accompanied by a high pH in the afternoon, therefore points to this mechanism rather than to a faulty reagent. It is one more reason to keep your pond above 5 °dKH.

Technical specifications

The essentials

Parameter measured: Carbonate hardness, denoted KHDissolved carbonates and bicarbonates, that is to say the buffering capacity of the water
Measurement principle: Titration, counting dropsNo fixed range, no colour chart: you add the reagent until the colour change and count the drops
Value of one drop: 1 °dKHThe number of drops is directly the carbonate hardness in German degrees
Equivalences: 1.78 °fH, 0.36 mmol/LOne drop also equals 21.8 mg/L of hydrogen carbonate
Minimum threshold: Never below 5 °dKH5 to 16 °dKH suits most freshwater tanks
Manufacturer's reference: JBL 2411000, PROAQUATEST rangeCode EAN 4014162241108

The procedure

Water volume: 5 mlThis is what sets one drop at 1 °dKH. A different volume changes the rule
The steps: Rinse, fill, dose drop by drop, countSwirl after each drop; if you don't, the colour change comes too late
Colour change: From blue to orange-yellowStop at the first drop that shifts the colour, not when the yellow turns fully clear
Waiting time: NoneThe colour change is instant, with no development time required
Total duration: Approximately 2 minutesIn water of average hardness
Environments covered: Freshwater, saltwater, pondThe reading method is the same throughout, as there is no colour chart to change

Security and parcels

Ranking: DangerThe single bottle is classified, and it is flammable
Main risks: Flammable, burns, eye damageH226, H314 and H318 statements
Precautions: Sink, well-ventilated room, out of reachChild-safety cap, keep away from all flames
Parcel weight: 0.09 kgPackaging included

To budget for separately

How to raise the KH: Potassium bicarbonateIt provides alkalinity and leaves potassium available to your crops
Reagent refill: Reagent only, ref. 2411100The graduated cylinder keeps well

10 further specifications are available in the detailed view.

In the box

1 bottle of KH reagent with child-safety cap
1 graduated plastic test tube from 5 to 20 ml
1 multilingual instruction leaflet, French included

Reference, EAN code, kit contents, protocol, value per drop, recommended minimum, range of 5 to 16 °dKH, and hazard statements taken from the manufacturer's datasheet and instructions on 05/09/2026. The alkalinity consumption by nitrification, 7.14 mg/L per mg/L of ammoniacal nitrogen, is a standard value in water treatment. The number of tests per bottle depends on the hardness of the water being analysed, since each test consumes as many drops as the water has degrees of hardness.

The buffer alone, or the complete kit?

Carbonate hardness is always measured alongside pH. The three columns differ in what they cover around this pair of parameters.

KH is the buffering capacity that limits pH from dropping Hard tap water carries a KH of 10 to 20 °dKH and varies little. Reverse osmosis water starts at 0, meaning the pH is no longer buffered once nitrification begins.

	Parameters covered (parameters)	Drop tests included (tests)	Carbonate hardness KH	pH, nitrites, nitrates and ammonium	Total hardness GH, iron, phosphates, copper, oxygen	Reagent bottles (bottles)	Glass test tubes	Laboratory comparator block	Thermometer	Reagent refill sold separately	Price
Recommended Carbonate hardness test onlyYour choice	1 parameters	1 tests	Yes	No	No	1 bottles	0	No	No	Yes	¥1,800
6-in-1 Aquarium Water Testing KitYour choice	6 parameters	5 tests	Yes	Yes	No	9 bottles	3	Yes	No	Yes	¥9,300
14-in-1 water analysis kit for aquariumYour choice	14 parameters	13 tests	Yes	Yes	Yes	23 bottles	12	Yes	Yes	Yes	¥21,700

Carbonate hardness test onlyRecommended

What you're measuring

Parameters covered (parameters)1 parameters

Drop tests included (tests)1 tests

Carbonate hardness KHYes

pH, nitrites, nitrates and ammoniumNo

Total hardness GH, iron, phosphates, copper, oxygenNo

Equipment supplied

Reagent bottles (bottles)1 bottles

Glass test tubes0

Laboratory comparator blockNo

ThermometerNo

Budget

Reagent refill sold separatelyYes

6-in-1 Aquarium Water Testing Kit

What you're measuring

Parameters covered (parameters)6 parameters

Drop tests included (tests)5 tests

Carbonate hardness KHYes

pH, nitrites, nitrates and ammoniumYes

Total hardness GH, iron, phosphates, copper, oxygenNo

Equipment supplied

Reagent bottles (bottles)9 bottles

Glass test tubes3

Laboratory comparator blockYes

ThermometerNo

Budget

Reagent refill sold separatelyYes

14-in-1 water analysis kit for aquarium

What you're measuring

Parameters covered (parameters)14 parameters

Drop tests included (tests)13 tests

Carbonate hardness KHYes

pH, nitrites, nitrates and ammoniumYes

Total hardness GH, iron, phosphates, copper, oxygenYes

Equipment supplied

Reagent bottles (bottles)23 bottles

Glass test tubes12

Laboratory comparator blockYes

ThermometerYes

Budget

Reagent refill sold separatelyYes

Parameters covered, equipment supplied and kit contents recorded from the three data sheets on 05/09/2026. A titration test uses neither a colour comparator block nor a glass measuring tube.

Documents & manuals

Official manufacturer's instructions, in French

Full titration test protocol, reference volume, endpoint reading rule and recommended values by installation type.

PDF · 1,5 Mo

Download

Estimate your
delivery time

Package weight 0.12 kg, dispatched to a collection point or by Colissimo to your home address, your choice at checkout. The reagent is sent in its original box. The exact shipping cost is shown in the basket.

Frequently asked questions

6 questions

6 key questions

My KH is too low — is that serious?

What is the difference between KH and GH?

Why is my KH dropping on its own?

How do you raise KH without increasing GH?

Use a hydrogen carbonate, not a calcium salt.
Potassium bicarbonate raises the KH and supplies potassium to your crops; sodium bicarbonate raises the KH without any other useful contribution.
For 1,000 L, allow approximately 36 g of potassium bicarbonate per degree of KH to gain.
Dissolve separately, pour slowly, and aim for no more than one degree per day.
Re-measure the following day, never immediately afterwards.

A limestone rock will do almost nothing as long as your pH stays above 7.

My water turns yellow on the very first drop — has the test expired?

Does this test measure the CO2 in my planted tank?

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KH carbonate hardness water test in drops

The summary