Blister pack for the JBL PROAQUATEST K refill, one liquid reagent and one powder reagent for the potassium test

Reagent refill for potassium K test

Name: Reagent refill for potassium K test
Brand: JBL
SKU: J2413100
Price: 3000.0 JPY
Availability: InStock

¥3,000

¥1,000 × 3 with no fees Klarna.

Potassium is the nutrient least well covered by fish food, which means it is often in short supply in aquaponics. These two reagents are those from the potassium test, for approximately 25 measurements.

The result is read by turbidity: add the reagent until a printed cross disappears. The two tubes, the syringe, the dual measuring spoon and the reading card from your kit remain in use.

Ref. J2413100·Reagent refill

Customer support 7 days a week by email

Delivery within 2 to 15 business days

100 % secure payment

The summary

What it measures: dissolved potassium, in milligrams per litre.
What the box contains: 2 reagent bottles, one liquid and one powder.
How to read the result: a printed cross disappears — no colour chart or shade comparison required.
How many tests: approximately 25, the same count as the original kit.
How much to sample: 15 ml drawn with a syringe, poured into the measurement tube.
Refill or complete kit: the refill is sufficient if both your tubes and your reading card are still intact.

Reagents K 1 and K 2, approximately 25 tests, result read by turbidity

Potassium is the macronutrient that actively growing plants consume in the greatest quantities, and they absorb it within hours. These two bottles, one liquid reagent and one powder reagent, are the reagents alone for the potassium test, providing approximately 25 measurements in freshwater and, after dilution, in saltwater.

This test does not involve comparing colours: potassium forms a whitish cloudiness with the reagents, and it is the height of liquid required to obscure a printed cross that gives the concentration. The natural colour of your water therefore has no effect on the reading, provided the water is clear to begin with, and you read the value directly from the graduated measuring tube in milligrams per litre.

🔬 A cross that disappears

Fill the 15 ml measuring tube with water using the syringe, then add 10 drops of reagent 1 and mix. Add one heaped measure of powder, taken with the wide end of the double-ended measure; this will make the water turn cloudy. Swirl gently for 30 seconds, leave to stand for 1 minute, then swirl once more. Place the glass test tube on the cross of the card and pour in the mixture until the cross is no longer visible from above; read the graduation at the bottom of the meniscus to obtain the concentration in mg/L.

The large powder measure should be levelled off

The powdered reagent is measured using the wide end of the double-ended scoop, and a heaped measure will distort the turbidity reading. Scrape the scoop level on the rim of the bottle before adding it, and measure away from any draught.

Saltwater

Dilute 10 ml of sample to 300 ml with distilled water, measure, then multiply the result by 30.

Glass reading tube

The graduated tube in mg/L is available as a spare part, so you don't need to buy the whole kit if it breaks.

A salt that supplies potassium and alkalinity

Use potassium bicarbonate alongside the refill if your reading remains below 10 mg/L. It raises both the potassium level and the carbonate hardness in a single dose, saving you from having to correct the same water twice. The carbonate hardness test lets you monitor the second value after each addition.

Both reagents are classified Danger, with the hazard statements H314 and H318, indicating severe skin burns and serious eye damage. Measure out the powder over a sink, without blowing on the measure to level it, and rinse immediately and thoroughly with water if any splashes into your eye. The treated tube should be emptied down the sink, never into your tank, and the bottles should be stored sealed, dry, at ambient temperature, and in their original packaging.

🌱 One element that feed covers poorly

Fish waste provides mainly nitrogen and phosphorus, while potassium remains too scarce to support plant growth, meaning it is often deficient in an aquaponic system. For healthy growth, the level should be around 10 mg/L, and up to 30 mg/L under intense lighting. Beyond that, filamentous algae take advantage of it, and an excessively high level becomes dangerous for sensitive species such as shrimps. The guide on plant deficiencies in aquaponics shows the discoloured leaf margins that indicate this shortfall.

📏 A gradually widening interval

At start-up, measure potassium every day until you know how quickly your plants consume it, then space out the checks once that rhythm is established. The 25 measurements in the refill kit are therefore concentrated in the first few weeks, whereas a stable system will make them last considerably longer. Always take readings at the same time of day, since your plants absorb potassium within a few hours and a measurement taken just after dosing is not comparable to the one from the day before.

Technical specifications

What the refill contains

Contents: 2 reagent bottlesOne liquid reagent and one powder reagent, numbered on the label.
Measurements: Approximately 25The same volume of reagent as in the original kit
Manufacturer's reference: JBL 2413100, PROAQUATEST rangeNot to be confused with 2413000, which is the complete kit
Corresponding test: Potassium K test, ref. 2413000The refill is used with the tubes, the syringe, the measuring spoon and the colour card from this test

Measuring potassium

Reading principle: Turbidity, not colourThe potassium precipitates as a whitish suspension, and it is the turbidity produced that gives the reading
Sample volume: 15 ml per measurementMeasured with a syringe, into the plastic measuring tube
Reagents to dose: 10 drops and 1 large level measureWide end of the dual measure spoon for powder
Duration of a measurement: Approximately 4 minutes30 seconds of shaking, 1 minute's rest, then pouring

Security and dispatch

Hazard classification: Warning, the 2 bottlesH314 and H318 labelling. Child-resistant caps on both
Storage: Store dry, at room temperatureBottles sealed tight, in their original packaging
Environments covered: Freshwater, saltwaterIn seawater, 10 ml diluted to 300 ml, result multiplied by 30
Parcel weight: 0.08 kgPackaging included

To budget for separately

Tubes, syringe and measuring spoon: Those from the potassium testThe collection tube is graduated in milligrams per litre — it is the tube that displays the result
Reading card: The one for the potassium testIt carries the reference cross, without which the pour cannot be read.

6 further specifications are available in the detailed view.

In the box

2 reagent bottles, one liquid and one powder

Reference, EAN code, contents, protocol, number of measurements and hazard statements checked against the JBL datasheet and instructions on 07/10/2026. Dilution beyond the graduation mark and spare measuring tube: JBL FAQ.

Two bottles, or the complete kit?

The refill and the kit contain the same reagent, follow the same protocol and give the same number of measurements. The decision depends on whether you already have the tubes, the measuring spoon and the reading card.

Turbidity is read from a card, not a colour chart The reading requires the reference cross, the graduated sampling tube in milligrams per litre and the measuring scoop for dosing the powder.

	Reagent bottles (bottles)	Possible readings (measurements)	Plastic measuring tube	Glass reading tube	Sampling syringe	Double measure	Cross-reference reading card	Price
Recommended Reagent refill for potassium K testYour choice	2 bottles	25 measurements	No	No	No	No	No	¥3,000
Potassium K drop water testYour choice	2 bottles	25 measurements	Yes	Yes	Yes	Yes	Yes	¥4,200

Reagent refill for potassium K testRecommended

What gets used up

Reagent bottles (bottles)2 bottles

Possible readings (measurements)25 measurements

What keeps well

Plastic measuring tubeNo

Glass reading tubeNo

Sampling syringeNo

Double measureNo

Cross-reference reading cardNo

Budget

Potassium K drop water test

What gets used up

Reagent bottles (bottles)2 bottles

Possible readings (measurements)25 measurements

What keeps well

Plastic measuring tubeYes

Glass reading tubeYes

Sampling syringeYes

Double measureYes

Cross-reference reading cardYes

Budget

Contents of both columns taken from the supplier's data sheet and instruction leaflet, on 05/09/2026.

Estimate your
delivery time

Parcel weight 0.08 kg, dispatched to a collection point or to your door, your choice at checkout. The bottles are sent in their original packaging. The exact postage cost is shown in the basket.

Frequently asked questions

6 questions

6 key questions

Why does this test require 15 ml of water?

How do you read a result without a colour chart?

Place the measuring tube over the cross printed on the reading card.
Pour the cloudy mixture in slowly, looking down from the top of the tube.
Stop at the precise moment the cross is no longer visible.
Read the graduation at the lower edge of the meniscus, in clear, diffused light.

The result is therefore not a colour comparison but a liquid depth, which makes this test unaffected by the colour of your water.

What should you do if the value exceeds the tube's graduation?

Dilute the sample with distilled water to 15 ml, repeat the measurement, then multiply the result.

Your water	Distilled water	Factor
7.5 ml	7.5 ml	× 2
3 ml	12 ml	× 5
1.5 ml	13.5 ml	× 10

For seawater, dilution is mandatory: 10 ml of sample made up to 300 ml, with the result multiplied by 30.

Why is potassium so often lacking in aquaponics?

Are the tubes and the measure spoon included in the refill?

How do you handle a powdered reagent classified as Danger?

Both bottles carry the H314 and H318 hazard statements: severe skin burns and eye damage. If splashed in the eye, rinse immediately and thoroughly with the eyelid held open.

The powder requires more care than the liquid. Measure it out away from draughts, over a sink, without blowing on the measuring spoon to level it. Screw the child-resistant caps back on fully, store the container up high in a dry place at room temperature, and take empty bottles to a recycling centre with household chemicals. Treated tubing can be rinsed down the sink.

Let us talk about your project

A question about this product or your setup? Our team will answer and advise you.

Email us Contact form

Interest-free instalment payments

Offered depending on the cart amount, at checkout.

Delivery in 2 to 15 working days

Depending on the products and shipping sites. Estimate by destination in the estimator on this page.

After-sales service 7 days a week by email or chat

Our team answers all your questions.

Shop responsibly

Become part of the change.

Reagent refill for potassium K test

The summary