Freshwater magnesium water test box, 10.6 by 17.5 cm format, labelled 60 measurements

Contents of the magnesium water test kit: comparator block, two glass test tubes, syringe, three reagent bottles and colour chart from 0 to over 10 mg per litre.

Reading the magnesium test: both test tubes placed in the comparator block, slid over the colour chart

The three reagent bottles of the freshwater magnesium test, numbered 1, 2 and 3

Magnesium Mg water test in drops, freshwater

Name: Magnesium Mg water test in drops, freshwater
Brand: JBL
SKU: J2414200
Price: 83.0 AED
Availability: InStock

Dhs. 83.00

Dhs. 27.66 × 3 with no fees Klarna.

This drop-based test measures magnesium from 0 to 10 mg/L in freshwater, whether in a planted aquarium or in aquaponics. Magnesium is the central atom of chlorophyll, and a plant deficient in it will yellow between the veins.

An iron deficiency produces the same yellowing, but it starts with the young leaves, whereas a magnesium deficiency starts with the lower leaves.

Ref. J2414200·Water test

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The summary

What you are measuring: dissolved magnesium, from 0 to 10 mg/L, across eight colour fields, in freshwater only.
Why measure it: aim for 5 to 10 mg/L for good growth. Very hard water can nonetheless contain very little.
What you receive: 3 bottles of reagents, 2 glass test tubes with screw caps, a syringe, a comparator block and a colour chart.
How long it takes: 3 minutes, and the colour stays readable for 15 minutes, no longer.
How to choose: a total hardness test adds calcium and magnesium together without separating them.
A corrosive reagent: bottle 2 contains caustic soda; once you have read the result, the test tube goes down the sink and never into the fish's water.

Drop test for magnesium from 0 to 10 mg/L, in fresh water, to distinguish between iron and magnesium deficiency

This drop test measures magnesium from 0 to 10 mg/L in fresh water, for about sixty measurements, and tells a magnesium shortfall apart from an iron deficiency in your crops. Aim for 5 to 10 mg/L. The result is read between 1 and 15 minutes on a sample, never in the fish's water.

A leaf that yellows between veins that have stayed quite green often makes people think of an iron deficiency first. Magnesium produces the same picture, however, so a chelate addition can go on for weeks without the foliage turning green again. This test tells the two apart in 3 minutes, over a range of 0 to 10 mg/L and for about sixty tests.

🍂 Lower leaves, upper leaves

The difference lies in how mobile the element is within the plant. Magnesium circulates in the sap and is remobilised from older tissues to growing organs as soon as the supply becomes insufficient, so the bottom of the plant turns pale first. Iron, on the other hand, barely circulates at all: once deposited in a leaf, it stays there, and the deficiency shows on the new leaves, at the top. So start by looking at where the yellowing begins on your plants, and you will know which of the two tests to use before you have even taken a single drop of sample.

🥬 The magnesium in chlorophyll

Every chlorophyll molecule is built around a single magnesium atom, and no other mineral can fill that role. A plant that lacks it produces less of the pigment that captures light, so its leaves turn pale and its growth stalls. Paleness is therefore the first sign to watch for on your plants, bearing in mind that this yellowing can have two causes.

The loss of colour begins between the veins because that is where the tissue responsible for photosynthesis is concentrated, while the veins themselves, made of conducting vessels, keep their colour for longer. This green network pattern on a pale background is the common signature of magnesium and iron deficiency, which is precisely why the eye alone cannot tell them apart. The article on deficiencies in aquaponics covers the neighbouring tables, including nitrogen, potassium and iron.

Remineralise without forgetting magnesium

Osmosis water remineralised with calcium alone shows a perfectly good GH and zero magnesium, which is a common imbalance in remineralised water. Epsom salt corrects precisely this imbalance, since it provides magnesium and sulphate with no carbonate at all and so leaves your buffering capacity untouched. A carbonate-based corrector, on the other hand, would raise the KH and the pH along the way.

Dosing Epsom salt to the gram

The useful dose is very small: 1 gram in 10 litres raises the magnesium level by about 10 mg/L, which is the entire scale of the colour chart in one go. Dose lightly, let a full filtration cycle circulate it, and only then test again. An excess can only be corrected by a partial water change, which takes far longer than this wait.

💧 What GH combines

Magnesium ions and calcium ions together make up the total hardness, which the GH test counts as a single block without ever telling them apart. A very hard tap water can therefore contain a lot of calcium and too little magnesium for aquatic plants, and nothing in the GH reveals it. That is the purpose of this test: it isolates the one fraction on which chlorophyll depends. On remineralised water, measure both: the GH gives the sum, this test the magnesium share.

🧪 When measuring is worthwhile

Yellowing starts at the bottom

The older leaves pale between green veins while the new growth looks fine. That is the classic picture of magnesium deficiency.

Yellowing starts from the top

New leaves come through pale while the lower ones stay green. Reach for the iron test, not this one.

Below 5 mg/L, plants do fine

This is not an emergency. Keep an eye on the leaf before correcting anything.

After remineralisation

A salt that supplies only calcium leaves the magnesium at zero. Test from the very first fill.

🧴 The bottle of sodium hydroxide

Of the three bottles, only the second is classified: it contains sodium hydroxide, caustic soda, which causes skin burns and eye damage. The first and third carry no hazard statement, which does not mean you may pour the test vial into the tank. Take the water into the vial, add the reagents in order, read between 1 and 15 minutes, then empty the sample down the sink and rinse the glass. In aquaponics, the same water irrigates your crops after passing through the fish, and a sample poured back would bring caustic soda into contact with both. The vials, the block and the colour chart last for years, and the Mg reagent refill replaces the three bottles.

Technical specifications

Measuring magnesium

Parameter measured: Dissolved magnesium, in mg/LThe colour chart is marked mg/L (ppm): the two units are equivalent in fresh water
Range and fields of the colour chart: 0, 1, 2, 3, 6, 8, 10 and over 10 mg/LEight fields, closer together at the bottom of the scale, across the values that need correcting
Target values: 5 to 10 mg/LRange for good growth of aquatic plants
Tests per kit: Around 60
Manufacturer's reference: JBL 2414200, PROAQUATEST range
Shaded surroundings: Freshwater onlySeawater measures around a thousand mg/L, far beyond this scale

The procedure

Water volume: 2 times 10 mlOne dosed test tube and one control test tube, read together in the block
The steps: Rinse, fill, add 1, add 2, add 3, readWith mixing between each addition of reagent
Drops per reagent: 7, then 3, then 2Three different measurements to note down before you begin
Waiting time: 1 minuteThe colour then stays stable for 15 minutes: read it within that window
Total time: About 3 minutesHandling included
Reading: Colour chart, in daylightThe block slides along the colour chart until the two shades match

Hazard labelling

Signal word: DangerOnly reagent 2 is classified, bottles 1 and 3 are not
Pictogram: Corrosive, GHS05That of reagent 2
Hazard statements: H314Skin burns and eye damage, caused by sodium hydroxide
Precautionary statements: P101, P102, P303+P361+P353, P305+P351+P338, P501Keep the label for the doctor, children kept away, skin and eyes rinsed, dispose of as required by regulations
Precautions: Sink, ventilated room, out of reachChild-resistant caps on all three bottles
Measured sample: Poured down the basinIt never goes back into the tank or the system

To allow for in addition

Enough to correct: Epsom salt, magnesium sulphate1 gram in 10 litres raises the magnesium content by about 10 mg/L: dose in small amounts
Reagent refills: Reagents only, ref. 2414300Three new bottles for the same glassware

12 further specifications are available in the detailed view.

In the box

3 bottles of reagents, fitted with child-resistant safety caps
2 glass test tubes with screw caps
1 graduated sampling syringe
1 laboratory comparator block, in grey
1 colour chart with 8 colour fields, from 0 to over 10 mg/L
1 multilingual instruction leaflet, French included

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

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.

Magnesium, or total hardness?

A total hardness test adds up calcium and magnesium without separating them. Here is what each column really tells you when your question is about magnesium.

GH adds calcium and magnesium together without separating them Two waters both showing 8 °dGH can contain, in one case, three times more magnesium than in the other. As long as you are dosing a salt yourself, the overall figure is no longer enough.

	Parameters covered	Magnesium measured separately, in mg/L	Calcium and magnesium counted together	The full nitrogen cycle	Reagent bottles	Glass test tubes	Laboratory comparator block	Colour chart	Time for a full analysis (minutes)	Reagent refill sold separately	Price
Recommended Magnesium-only testYour choice	1	Yes	No	No	3	2	Yes	Yes	3 minutes	Yes	Dhs. 83.00
GH water test, total hardness, drop-basedYour choice	1	No	Yes	No	1	0	No	No	2 minutes	Yes	Dhs. 42.00
JBL ProAquaTest Lab water analysis case, 13 tests for aquarium and pondYour choice	12	No	Yes	Yes	23	12	Yes	Yes	30 minutes	Yes	Dhs. 417.00

Magnesium-only testRecommended

What the measurement tells you

Parameters covered1

Magnesium measured separately, in mg/LYes

Calcium and magnesium counted togetherNo

The full nitrogen cycleNo

Equipment supplied

Reagent bottles3

Glass test tubes2

Laboratory comparator blockYes

Colour chartYes

Application

Time for a full analysis (minutes)3 minutes

Reagent refill sold separatelyYes

GH water test, total hardness, drop-based

What the measurement tells you

Parameters covered1

Magnesium measured separately, in mg/LNo

Calcium and magnesium counted togetherYes

The full nitrogen cycleNo

Equipment supplied

Reagent bottles1

Glass test tubes0

Laboratory comparator blockNo

Colour chartNo

Application

Time for a full analysis (minutes)2 minutes

Reagent refill sold separatelyYes

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

What the measurement tells you

Parameters covered12

Magnesium measured separately, in mg/LNo

Calcium and magnesium counted togetherYes

The full nitrogen cycleYes

Equipment supplied

Reagent bottles23

Glass test tubes12

Laboratory comparator blockYes

Colour chartYes

Application

Time for a full analysis (minutes)30 minutes

Reagent refill sold separatelyYes

Contents of the tests and the kit taken from the comparison data sheets. The 13-test kit includes three pH tests and reads CO2 from a table.

Documents & manuals

Official manufacturer's instructions, in French

Six-step protocol, volumes and number of drops reagent by reagent, target value for plant growth, and what to do when the result is too low or too high.

PDF · 1,6 Mo

Download

Estimate your
delivery time

Parcel weighing 0.17 kg, dispatched within 48 h by Colissimo or Chronopost to your home, as you choose during checkout. The reagents are sent in their original box, upright. The exact cost is shown in your basket. Once unsealed, this product cannot 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

8 questions

6 key questions, 8 in the detailed view

My leaves are turning yellow between the veins, is it iron or magnesium?

Three deficiencies cause yellow foliage, and the location of the symptom tells all three apart.

Where it starts	Appearance	The element
New leaves, at the top	Pale blade, green veins	Iron
Old leaves, at the bottom	Paleness between the veins	Magnesium
Old leaves, at the bottom	Edge that yellows then dries out	Potassium

Iron moves very little within the plant, whereas magnesium and potassium move freely. This is why iron affects the top and the other two the bottom.

What magnesium level should you aim for?

My GH is fine, can I still be short of magnesium?

How can you increase magnesium without changing the rest of the water?

Why does the colour remain readable for only 15 minutes?

Is an excess of magnesium dangerous?

It is not, at the doses of a sensible addition to freshwater. The practical risk is losing the scale: above 10 mg/L the colour chart can no longer tell values apart, and you will not know where you stand until part of the water has been changed.

The hazard lies rather with reagent 2 of the test, which is corrosive: it stays in the test tube, which is emptied down the sink, and it never goes into the fishes' water.

What calcium to magnesium ratio should be observed?

Why is this test for freshwater only?

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Magnesium Mg water test in drops, freshwater

The summary