Blister pack for the JBL PROAQUATEST KH refill, a carbonate hardness titration reagent bottle

Reagent refill for KH carbonate hardness test

Name: Reagent refill for KH carbonate hardness test
Brand: Hardy Dewerse
SKU: J2411100
Price: 7.0 USD
Availability: InStock

$7.00

$2.33 × 3 with no fees Klarna.

This bottle is the titration reagent for the carbonate hardness test, sold separately. You add it drop by drop to 5 ml of water until the colour changes from blue to orange-yellow.

The number of drops added gives the result directly, at a rate of 1 °dKH per drop. The test tube from your kit remains in use, and there is no colour chart to replace with a titration method.

Ref. J2411100·Reagent refill

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The summary

What it measures: carbonate hardness, i.e. the buffering capacity of your water.
What the box contains: 1 bottle of titration reagent.
How to read the result: count the drops until the colour change — no colour chart needed.
How many tests: the softer your water, the more tests you get, as each degree uses one drop.
What to aim for: 5 to 16 °dKH in freshwater, at least 5 in a pond.
Reading to half a degree: using 10 ml of water, one drop equals 0.5 °dKH.

The titration bottle on its own, one drop equals 1 °dKH per 5 ml of water

Carbonate hardness, or KH, measures the dissolved hydrogen carbonates in your water, that is, its capacity to neutralise acids without the pH shifting. This bottle is the titration reagent alone from the drop-based KH test kit, and it is used with the test tube from your kit.

🔢 One drop, one degree

Fill the test tube with 5 ml of water, then add the reagent drop by drop, swirling after each drop, until the colour changes from blue to orange-yellow. The number of drops added gives the carbonate hardness directly in German degrees, so no colour chart is needed. One drop also corresponds to 1.78 °fH, an alkalinity of 0.36 mmol/L and 21.8 mg/L of hydrogen carbonates, which allows you to compare your result with a mains water analysis report.

Per 10 ml of water

By doubling the sample volume, each drop is worth only 0.5 °dKH, which refines the reading for soft water.

One bottle matched to your water

Each test uses as many drops as the water has degrees of hardness, so soft water uses the bottle more slowly.

🦠 A reserve that bacteria consume

Most freshwater fish and plants do well between 5 and 16 °dKH, and a garden pond requires at least 5 °dKH. In aquaponics, this reserve naturally declines, as the bacteria that convert ammonium into nitrate consume alkalinity, approximately 7.14 mg/L expressed as calcium carbonate for every milligram per litre of ammoniacal nitrogen. The larger the feed ration given to the fish, the more frequently this measurement should be taken, and the guide on the nitrogen cycle covers this reaction in detail.

The first turn to yellow stops the count

Stop counting at the first drop that shifts the colour to orange-yellow, not when a clean yellow appears. Swirl after each drop; if you do not, the colour change comes too late and your result will read too high. Also take care not to confuse this bottle with the total hardness reagent, which changes from red to green.

Raise alkalinity with potassium bicarbonate

When your reading drops below 5 °dKH, potassium bicarbonate raises the carbonate hardness whilst supplying potassium to your plants, which are often deficient in it in aquaponics. Dose it in small amounts, then carry out a titration the following day using this same test kit to verify the effect. The pH test completes the picture, as it shows the pH that your carbonate hardness is maintaining.

🧯 A corrosive and flammable reagent

The reagent is classified as Danger, with hazard statements H314, H318, and H226: it causes severe skin burns and eye damage, and is a flammable liquid. Work over a sink, replace the child-resistant cap after each series of tests, and store the bottle in a dry place at room temperature in its original packaging. Always keep it upright, nozzle facing down and dry on the outside, as a drop that exits with an air bubble counts as a full drop and will shift your result by one degree.

Technical specifications

What the refill contains

Contents: 1 reagent bottleKH titration reagent, child-safety cap
Corresponding test: KH carbonate hardness test, ref. 2411000The refill is used with the test tube supplied with this test

Counting the drops

Value of one drop: 1 °dKH per 5 mlOver 10 ml, one drop equals 0.5 °dKH
Colour change: From blue to orange-yellowStop at the first drop that causes the colour to shift.

Reference and safety

Manufacturer's reference: JBL 2411100, PROAQUATEST rangeNot to be confused with 2411000, which is the complete test kit
Hazard classification: Danger, single bottleHazard statements H226, H314 and H318. Store dry, cap tightly closed, away from all ignition sources

To budget for separately

Test tube: That of the carbonate hardness testFilled to 5 ml, or to 10 ml for half-degree readings
How to raise the KH: Potassium bicarbonateIt provides alkalinity and leaves potassium available to your crops

In the box

1 bottle of KH titration reagent, with child-resistant cap

Reference, EAN code, contents, protocol, number of measurements and hazard statements taken from the JBL product sheet and instructions on 07/10/2026. The 10 ml reading is from the JBL FAQ. The alkalinity consumption by nitrification, 7.14 mg/L as CaCO3 per mg/L of ammonia nitrogen, is a standard value in water treatment.

Documents & manuals

Official manufacturer's instructions, in French

Full titration test protocol, reference volume and endpoint reading rule. This is the kit's instruction leaflet: it applies equally to the refill, which contains the same reagent.

PDF · 1,5 Mo

Download

Estimate your
delivery time

Package weight 0.02 kg, dispatched to a collection point or to your home address, your choice at checkout. The bottle is sent in its original packaging. The exact shipping cost is shown in the basket.

Frequently asked questions

6 questions

6 key questions

Why does the number of readings depend on my water?

Because it is a titration. Each test consumes as many drops as the water has degrees, so soft water uses the bottle slowly while hard water uses it quickly.

Your water	Drops per test
Soft water, 5 °dKH	5
Medium water, 8 °dKH	8
Hard water, 16 °dKH	16

The same bottle therefore yields roughly three times as many tests with the first water as with the third.

What carbonate hardness should you aim for?

Should you correct KH before pH?

My water analysis gives a TAC in °f — how do I compare?

Divide the value in French degrees by 1.78 to obtain German degrees, as one drop of this reagent equals 1 °dKH, or 1.78 °fH.

Your local water report	Expected drops
TAC 9 °f	5
TAC 18 °f	10
TAC 28 °f	16

One drop also corresponds to an alkalinity of 0.36 mmol/L, the unit used in some laboratory reports.

Is the test tube included in the refill?

Why does alkalinity drop on its own?

Because nitrification consumes it. The bacteria that convert ammonium to nitrate consume approximately 7.14 mg/L of alkalinity, expressed as calcium carbonate, for every milligram per litre of ammoniacal nitrogen processed — a standard figure in water treatment.

In a system where the fish are receiving a substantial ration, this consumption is continuous, so this parameter needs routine monitoring, not just at start-up. The nitrogen cycle guide covers the reaction in detail.

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Reagent refill for KH carbonate hardness test

The summary