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

JBL ProAquaTest magnesium drop water test, freshwater

Name: JBL ProAquaTest magnesium drop water test, freshwater
Brand: JBL
SKU: J2414200
Price: 19.9 EUR
Availability: InStock

19,90 €

Effectively monitor magnesium levels with this reliable JBL PROAQUEST Mg magnesium water test , essential for optimal balance in saltwater aquariums.

Ref. J2414200·Water test

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The summary

What you measure: dissolved magnesium, from 0 to 10 mg/L, across eight colour fields, in fresh water only.
Why measure it: aim for 5 to 10 mg/L for good growth. Very hard water may nonetheless contain little of it.
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.
What is sent to you: a 0.17 kg parcel, reagents in their original box.

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

The JBL magnesium water test in drops, from the PROAQUATEST range, measures dissolved magnesium from 0 to 10 mg/L in freshwater, in planted aquariums as well as in aquaponics. It gives a result in 3 minutes for around sixty tests. It helps you tell a magnesium shortage, which first yellows the lower leaves, from an iron deficiency, which shows on the young leaves.

A leaf that yellows between veins that have stayed perfectly green often suggests an iron deficiency first. Magnesium produces the same picture, however, so a chelate supplement 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 around sixty measurements.

🍂 Lower leaves, upper leaves

The difference lies in how mobile the element is within the plant. Magnesium travels in the sap and is remobilised from older tissue to growing organs as soon as the supply becomes insufficient, so the bottom of the plant turns pale first. Iron, by contrast, barely moves 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 reach for before you have even drawn a single drop of water.

🥬 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, provided you know that this kind of yellowing can have two causes.

The loss of colour starts between the veins because that is where the tissue responsible for photosynthesis is concentrated, whereas the veins themselves, made of conducting vessels, keep their colour for longer. This pattern of a green network on a pale background is the shared signature of magnesium and iron, which is exactly 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 correct GH and zero magnesium, which is a common imbalance in remineralised water. Epsom salt corrects precisely this imbalance, since it supplies magnesium and sulphate without any carbonate and so leaves your buffering capacity intact. A carbonate-based corrector, on the other hand, would raise the KH and the pH along the way.

Dose the 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, that is, the whole colour chart scale in a single go. Dose small, let it circulate through one complete filtration cycle, and only then measure again. An excess can only be corrected by a partial water change, which takes far longer than this wait.

💧 What the GH blends

Magnesium ions and calcium ions together make up the total hardness, which the GH test counts as a single block without ever distinguishing between them. 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 whole purpose of this test: it isolates the one fraction on which chlorophyll depends. On remineralised water, then, measure both: the GH gives the sum, and this test gives the magnesium share.

🧪 When testing is worth it

Yellowing starts at the bottom

The old leaves turn pale between green veins, while the new shoots are fine. This is the magnesium table.

Yellowing starts from the top

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

Under 5 mg/L, plants do reasonably well

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

After remineralisation

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

Technical specifications

The essentials

Parameter measured: Dissolved magnesium, in mg/LThe colour chart is marked mg/l (ppm): the two units are equivalent in fresh water
Measurement range: 0 to 10 mg/L, plus a range beyond thatThe steps get finer at the bottom of the scale, on the values to be corrected
The colour chart fields: 0, 1, 2, 3, 6, 8, 10 and over 10Eight values, the last field being recorded as more than 10 mg/L
Target values: 5 to 10 mg/LRange for good growth of aquatic plants
Tests per kit: Approximately 60
Manufacturer's reference: JBL 2414200, PROAQUATEST range

The procedure

Water volume: 2 times 10 mlOne treated sample and one untreated blank, side by side in the comparator block
The steps: Rinse, fill, dose 1, dose 2, dose 3, readWith a mix 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: take your reading within that window
Total duration: Approximately 3 minutesHandling included
Reading: Colour chart, in daylightThe block slides along the colour chart until the two shades match

Safety and environment

Ranking: DangerOnly reagent 2 is classified; it contains sodium hydroxide
Main risks: Burns, eye injuriesH314 and H318 statements
Precautions: Sink, well-ventilated room, out of reachChild-resistant caps on all three bottles
Covered environment: Freshwater onlySeawater measures around a thousand mg/L, far beyond this scale

To budget for separately

What to correct with: Epsom salt, magnesium sulphate1 gram in 10 litres raises the magnesium content by about 10 mg/L: dose sparingly
Reagent refill: Reagents only, ref. 2414300The glassware, comparator block and colour chart can be kept

10 further specifications are available in the detailed view.

In the box

3 reagent bottles with child-resistant 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

Reference, EAN code, number of tests, kit contents, six-step protocol, target value and hazard statements taken from the manufacturer's data sheet and instructions on 05/09/2026. The range of 0 to 10 mg/L and the detail of the eight fields are taken from a photograph of the colour chart supplied.

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 calcium and magnesium together without separating them. Here is what each column really tells you when your question is about magnesium.

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

	Parameters covered (parameters)	Magnesium dosed separately, in mg/L	Calcium and magnesium counted together	The complete nitrogen cycle	Reagent bottles (bottles)	Glass test tubes	Laboratory comparator block	Colour chart	Duration of a full analysis (minutes)	Reagent refill sold separately	Price
Recommended Magnesium-only testYour choice	1 parameters	Yes	No	No	3 bottles	2	Yes	Yes	3 minutes	Yes	19,90 €
JBL ProAquaTest GH total hardness dropYour choice	1 parameters	No	Yes	No	1 bottles	0	No	No	2 minutes	Yes	9,90 €
13-in-1 water testing kit for aquariumsYour choice	12 parameters	No	Yes	Yes	23 bottles	12	Yes	Yes	30 minutes	Yes	99,90 €

Magnesium-only testRecommended

What testing teaches you

Parameters covered (parameters)1 parameters

Magnesium dosed separately, in mg/LYes

Calcium and magnesium counted togetherNo

The complete nitrogen cycleNo

Equipment supplied

Reagent bottles (bottles)3 bottles

Glass test tubes2

Laboratory comparator blockYes

Colour chartYes

Setting up

Duration of a full analysis (minutes)3 minutes

Reagent refill sold separatelyYes

JBL ProAquaTest GH total hardness drop

What testing teaches you

Parameters covered (parameters)1 parameters

Magnesium dosed separately, in mg/LNo

Calcium and magnesium counted togetherYes

The complete nitrogen cycleNo

Equipment supplied

Reagent bottles (bottles)1 bottles

Glass test tubes0

Laboratory comparator blockNo

Colour chartNo

Setting up

Duration of a full analysis (minutes)2 minutes

Reagent refill sold separatelyYes

13-in-1 water testing kit for aquariums

What testing teaches you

Parameters covered (parameters)12 parameters

Magnesium dosed separately, in mg/LNo

Calcium and magnesium counted togetherYes

The complete nitrogen cycleYes

Equipment supplied

Reagent bottles (bottles)23 bottles

Glass test tubes12

Laboratory comparator blockYes

Colour chartYes

Setting up

Duration of a full analysis (minutes)30 minutes

Reagent refill sold separatelyYes

Parameters covered, equipment supplied and kit contents taken from the three data sheets on 05/09/2026. The 13-in-1 kit combines 13 drop tests, three of them for pH, plus CO2 read from a chart.

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 yellowing between the veins, is it iron or magnesium?

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

Where it starts	Appearance	The element
New leaves, at the top	Pale leaf 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. That is why iron marks 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 I raise magnesium without changing the rest of the water?

Why does the colour stay readable for only 15 minutes?

Is an excess of magnesium dangerous?

What calcium to magnesium ratio should be maintained?

Why is this test only for freshwater?

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JBL ProAquaTest magnesium drop water test, freshwater

The summary