Because each measurement uses 15 ml of water and one scoop of powder, compared with just a few drops for a colorimetric test. This is not a weekly test: measure every day at the start, until you know how quickly your plants consume nutrients, then space your readings out considerably.

Front-facing view of the potassium K water test box on a white background, labelled 25 tests

The two reagent bottles for the potassium K test — the liquid and the powder — on a white background

Diagram of potassium deficiency: the edges of older lower leaves turn brown while the new growth remains green

Diagram of turbidity reading: three graduated tubes filled to different levels for 2, 8 and 15 mg/L of potassium

Potassium K drop water test

Name: Potassium K drop water test
Brand: JBL
Price: 23.0 USD
Availability: InStock

$23.00

Fish produce almost no potassium, while plants consume a great deal: a closed system therefore drifts mechanically towards deficiency, even when no other parameter changes.

This test gives the value in mg/L, from 2.0 to 15, without a colour chart: you add the cloudy water until a printed cross disappears, then read the graduation reached.

7/7 customer service by e-mail

Payment in instalments, free of charge

The summary

Why this test exists: potassium is the only macronutrient that a closed system does not produce, because fish excrete virtually none of it.
What you receive: 2 reagent bottles, a graduated measuring tube, a glass reading tube, a syringe, a double scoop and a reading card.
How to read it: by turbidity. You add the sample until a printed cross is obscured, then read the graduation. The less you need to add, the higher the potassium level.
How long it takes: four minutes per measurement — the fastest test in the range.
How to choose: it is the only one of the three major nutrients purchased separately.
What gets sent to you: a 0.12 kg parcel, reagents in their original packaging.

Dissolved potassium test from 2.0 to 15 mg/L, read by turbidity, for aquaponics and planted tanks

In a planted aquarium, potassium can be topped up with a liquid fertiliser and the matter ends there. In aquaponics, the question is quite different. Nitrogen arrives on its own and in abundance through fish waste, whereas potassium barely arrives at all: the fish absorbs it for its own needs and the feed is formulated with very little to spare. The better your system runs, the faster the plants grow, and the faster the potassium level drops. This explains a system with comfortable nitrate levels whose lettuces simply refuse to grow.

🔬 A turbidity-based reading

This test does not rely on a colour scale. The second reagent causes potassium to precipitate as a whitish suspension, which becomes denser the more potassium the water contains, and it is this opacity that serves as the measure. You place the glass reading tube on the printed cross supplied with the kit, then pour in the cloudy water until the cross, viewed from above, disappears. The height reached gives the reading, which leads to a result that can seem counterintuitive at first: the less you need to pour, the higher the concentration. Read under clear, diffuse light, at the lower edge of the meniscus. Since no colour shade needs to be distinguished, two people looking at the same tube will read the same value.

Low value, plants at a standstill

The common scenario in aquaponics. A dose is needed, and the test tells you how much.

Low reading, plants in good health

Nothing to correct. On a poorly lit tank, a low reading is not a deficiency.

High value with no input

Check your top-up water first, or a fertiliser that is already high in potassium.

Beyond 15 mg/L

Dilute 10 ml in 300 ml of distilled water, then multiply the result by 30.

🥬 What the deficiency reveals

Potassium moves freely through the sap, so it is remobilised from older tissue towards growing organs as soon as the supply becomes insufficient. The deficiency therefore shows up on the lower leaves, whose edges yellow and then die back while the young shoots retain their colour. Iron follows exactly the opposite logic: it stays fixed where it was deposited and causes deficiency symptoms to appear at the top of the plant. Looking first at where the yellowing starts helps you avoid reaching for the wrong test kit, and our article on deficiencies in aquaponics covers the other patterns in detail.

Already cloudy water skews the reading

The reading relies entirely on the opacity produced after the reaction, which means the water must be clear to begin with. Water carrying particles, a bacterial haze or fine grow medium residue will give an artificially high reading with no indication that anything is wrong. Allow your sample to settle, or filter it, before you start. This is the only real drawback of this method compared with a colorimetric test, which tolerates slightly turbid water.

Correcting potassium and alkalinity in a single step

Nitrification consumes alkalinity, so an aquaponic system loses its buffering capacity at the same time as it loses its potassium. Both drifts can be corrected together with potassium bicarbonate: the hydrogen carbonate ion raises the KH while the potassium ion feeds the crops. No other pH corrector delivers this dual benefit, which is worth knowing before buying two separate products. The carbonate hardness test provides the second value from the same water sample.

🧪 How often to measure

Potassium levels do not fluctuate from one day to the next the way nitrite levels do during cycling: they fall slowly, in line with plant growth, then rise sharply after a dose is added. A monthly test is therefore sufficient on a stable setup like yours, provided you retest as soon as a symptom appears on the lower leaves or immediately after a significant harvest. Test again a few days after adding a supplement, since it is the difference between your two readings that shows what your crops are actually consuming. The 25 tests in the kit therefore cover a good two seasons of monitoring.

🌊 Potassium alongside other parameters

A potassium reading should never be interpreted in isolation, because three elements together govern leaf growth. Nitrogen, supplied free of charge by the fish, is rarely the limiting factor; potassium almost always is; iron becomes limiting as soon as pH rises. A system with comfortable nitrate levels whose plants are still stalling has therefore depleted one of the other two, and two tests are enough to find out which. The iron test covers the remaining half of cases.

Technical specifications

The essentials

Parameter measured: Dissolved potassium, in mg/LThe only one of the three major nutrients that fish waste does not supply
Reading range: 2.0 to 15 mg/LBeyond this, dilute 10 ml in 300 ml of distilled water and multiply by 30
Method: Turbidity, not colorimetryPotassium precipitates as a whitish suspension: it is the opacity produced that gives the reading
Reading the result: Disappearance of a printed crossViewed from above, in clear diffuse light, at the lower edge of the meniscus
Tests per kit: Around 25One measurement per day to begin with, while you establish your plants' consumption pattern, then space them out
Manufacturer reference: JBL 2413000, PROAQUATEST rangeCode EAN 4014162241306

The procedure

Sample volume: 15 ml per measurementThe largest volume in the range, drawn with a graduated measuring tube rather than a syringe.
The steps: Rinse, draw, dose, shake, wait, pour, readIn that order. It is the final addition that gives the reading, not the colour already obtained
Reagents to dose: 10 drops and 1 level measureReagent 1 is liquid, reagent 2 is powder. A heaped dose will skew the reading.
Agitation and rest: 30 s, then 1 minThe precipitate must be uniform before pouring
Total duration: Approximately 4 minutesThe fastest test in the range
Media covered: Freshwater, pond, saltwaterIn salt water, dilution to one-thirtieth is mandatory

Security and parcels

Ranking: DangerBoth reagent bottles are classified — this is the only test in the range where that applies
Main risks: Burns, eye injuriesH314 and H318 statements
Precautions: Sink, ventilated room, out of reachThe powder for reagent 2 should be measured away from draughts, as it disperses easily.
Parcel weight: 0,12 kgPackaging included

To budget for separately

What to correct with: Potassium bicarbonateIt raises potassium and carbonate hardness in a single addition
Reagent refill: Reagents only, ref. 2413100The two tubes, the syringe, the measuring spoon and the colour chart can all be stored.

10 further specifications are available in the detailed view.

In the box

2 reagent bottles, one liquid and one powder
1 plastic measuring tube, graduated from 5 to 20 ml
1 glass sampling tube, graduated in mg/L of potassium
1 graduated sampling syringe
1 double-ended measure, one wide end and one narrow
1 reading card bearing the reference cross, with multilingual instructions including English

Reference, EAN code, number of tests, kit contents, seven-step protocol, dilution rule, and hazard statements taken from the manufacturer's data sheet and instructions on 05/09/2026. The range of 2.0 to 15 mg/L comes from older manufacturer documentation, reproduced by retailer listings. Recommended values in aquaponics vary considerably depending on the source, from 10 to over 100 mg/L.

What this test adds to any kit

Potassium is the only one of the three major nutrients that neither kit measures. This test sits alongside them rather than replacing them.

Fish waste provides almost no potassium Nitrogen and phosphorus come in with the feed; potassium does not. It is the first element to run short as soon as a plant starts to fruit.

	Potassium measured	Parameters covered (parameters)	Drop tests included (tests)	pH, KH, nitrites and nitrates	GH, iron, phosphates, copper, silicates, oxygen	Reagent bottles (bottles)	Glass test tubes	Laboratory comparator block	Thermometer	Reagent refill sold separately	Price
Recommended Potassium test aloneYour choice	Yes	1 parameters	1 tests	No	No	2 bottles	1	No	No	Yes	$23.00
6-in-1 Aquarium Water Testing KitYour choice	No	6 parameters	5 tests	Yes	No	9 bottles	3	Yes	No	Yes	$50.00
14-in-1 water analysis kit for aquariumYour choice	No	14 parameters	13 tests	Yes	Yes	23 bottles	12	Yes	Yes	Yes	$104.00

Potassium test aloneRecommended

Potassium

Potassium measuredYes

Parameters covered (parameters)1 parameters

Drop tests included (tests)1 tests

What each kit covers

pH, KH, nitrites and nitratesNo

GH, iron, phosphates, copper, silicates, oxygenNo

Equipment supplied

Reagent bottles (bottles)2 bottles

Glass test tubes1

Laboratory comparator blockNo

ThermometerNo

Budget

Reagent refill sold separatelyYes

6-in-1 Aquarium Water Testing Kit

Potassium

Potassium measuredNo

Parameters covered (parameters)6 parameters

Drop tests included (tests)5 tests

What each kit covers

pH, KH, nitrites and nitratesYes

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

14-in-1 water analysis kit for aquarium

Potassium

Potassium measuredNo

Parameters covered (parameters)14 parameters

Drop tests included (tests)13 tests

What each kit covers

pH, KH, nitrites and nitratesYes

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 covered, equipment supplied and kit contents recorded from the three product sheets on 05/09/2026.

Documents & manuals

Official manufacturer's instructions, in French

Full seven-step protocol, 15 ml volume, reading rule at the lower meniscus, one-in-thirty dilution and recommended potassium values.

PDF · 1,5 Mo

Download

Estimate your
delivery time

Package weight 0.12 kg, dispatched to a collection point or via Colissimo to your door — your choice at checkout. Reagents are sent in their original packaging, tubes and accessories included. The exact cost is shown in your basket.

Frequently asked questions

8 questions

6 key questions, 8 in the detailed view

What potassium level should you aim for?

Why is potassium always in short supply in aquaponics?

How do you identify a deficiency on your plants?

Edges of old leaves or young shoots: potassium or iron?

Potassium moves through the plant; iron does not. A plant short of potassium draws it from its older leaves to supply new growth, so the symptom appears at the bottom, starting at the edges. A plant short of iron has nothing to redistribute, so the symptom appears at the top, on new leaves, between the veins. Look first at where the yellowing starts — that alone will often spare you from having to test for both.

How do you add potassium without upsetting the rest of the water chemistry?

Measure your potassium and carbonate hardness on the same day.
If both are low, use potassium bicarbonate: it corrects both at once.
Add it in small doses, spread over several days.
Re-test twenty-four hours after the final dose, never immediately afterwards.

Potassium sulphate raises potassium without affecting the buffer — the right choice when your carbonate hardness is already where it should be.

How do you measure beyond 15 mg/L?

Can an excess of potassium cause problems?

Why only 25 tests?

Let us talk about your project

Une question sur ce produit ou votre installation ? Notre équipe vous répond et vous conseille.

Email us Contact form

Paiement plusieurs fois sans frais

Proposé selon le montant du panier, au moment du paiement.

Livraison sous 5 à 15 jours ouvrés

Selon les produits et sites d'expédition. Estimation par destination dans l'estimateur de cette page.

SAV 7/7 par mail ou chat

Notre équipe répond à toutes vos questions.

Faire un achat engagé

Devenez acteurs du changement.

Potassium K drop water test

The summary