Cardboard box for the iron Fe drop test, labelled 50 tests, for aquarium, pond and saltwater

Contents of the iron test kit: grey comparator block, two glass test tubes, syringe, reagent bottle, and colour chart

Colour chart for the iron test placed under the comparator block and its two test tubes, nine colour fields from 0.02 to 1.5 mg per litre

Adding the five drops of reagent to the test tube placed in the comparator block, above the colour chart

Drop-bottle of iron Fe reagent, white cap, alone on a white background

Iron Fe water test in drops

Name: Iron Fe water test in drops
Brand: Hardy Dewerse
SKU: J2411600
Price: 19.0 USD
Availability: InStock

$19.00

$6.33 × 3 with no fees Klarna.

Iron is one of the first elements to run short in an aquaponic system, and its deficiency shows in the foliage. This test gives the truly dissolved iron, from 0.02 to 1.5 mg/L, in 12 minutes.

The manufacturer recommends one measurement per week after filling. Around an addition, one measurement just before and another 24 to 48 hours afterwards show you what your system really consumes.

Ref. J2411600·Water test

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The summary

What you receive: a bottle of reagent, two glass test tubes, a syringe, a grey comparator block and the colour chart, for around 50 tests.
What you read: dissolved iron, from 0.02 to 1.5 mg/L, across nine colour fields, in fresh water, in ponds and in sea water.
What level to aim for: 0.1 to 0.2 mg/L in a planted aquarium, around 2 mg/L for the crops of an aquaponic system according to the FAO, and 0.05 mg/L at most in sea water.
When to test: just before an addition, then one to two days afterwards. In two readings you know your actual consumption.
How to choose: iron is included in the 13 in 1 case, not in the 6 in 1.
What is sent to you: a 0.13 kg parcel, with the bottle and glassware wedged in the original box.

Drop test for dissolved iron, from 0.02 to 1.5 mg/L, for managing chelate dosing

In aquaponics, fish feed provides very little iron, making it the most common deficiency in grow beds. It shows up visually well before it can be measured, provided you look at the right part of the plant, as three other deficiencies produce a similar yellowing of the foliage. This test measures the iron actually dissolved in your system's water and allows you to draw a firm conclusion.

🍃 Where the yellowing starts

Iron is one of the least mobile elements within a plant. Once fixed in a leaf, it is no longer redistributed to younger organs, so the deficiency appears on the uppermost leaves, where the blade turns pale between veins that remain green. The oldest leaves lower down the stem may meanwhile stay perfectly green for several weeks. By contrast, nitrogen and magnesium travel through the sap and are drawn back towards new growth, so their deficiency starts at the bottom of the plant. Observing where the yellowing begins therefore remains the only reliable first step before any testing, and the guide on iron deficiency in aquaponics covers this species by species.

🧲 Precipitation and chelate form

There remains a chemical constraint that governs the choice of product. In aerated water, unchelated iron does not stay in solution; above pH 6.5, it oxidises and precipitates within a few hours. An aquaponic system combines precisely these two conditions, since it brings together heavily oxygenated water and a pH that most often stays above 6.5. A zero reading taken the day after dosing therefore indicates precipitation rather than plant uptake, and telling the two apart completely changes how you should respond. This is why iron is sold in chelated form, with a complexing molecule keeping it dissolved; and since each chelating agent has a pH threshold beyond which it releases the iron, the form you choose should be based on the pH of your water rather than on the measured iron level.

EDTA 13 %

Lowest pH threshold. Reserved for acidic water, it releases iron as soon as pH rises.

DTPA 11 %

The standard compromise, stable up to neutral to slightly alkaline water.

EDDHA 6 %

Upper pH limit, for hard water. It turns the water red.

Preliminary measurement

Measure your water's pH before buying the chelate, as it is the pH that determines the correct form.

The ammonium reagent skews the iron reading

A trace of ammonium test reagent left in a test tube will push the iron reading upward, and this is by far the most common cause of an abnormally high result. Rinse your test tubes three times with the water you are testing before each measurement, and avoid using the same glassware for both tests without that rinse. Dedicated glassware for each parameter remains the safest approach once you are monitoring several values.

Choose the chelate form before the dose

pH determines whether an iron supplement will remain available or precipitate, making it the measurement to take before you even place your order. The liquid pH test can be carried out on the same water sample. Above pH 7, the EDDHA 6% chelate remains stable where an EDTA has already released its iron, whereas between 6 and 7, DTPA 11% is sufficient and does not colour the water. Choosing the right form based on pH, rather than picking one at random off the shelf, means you avoid repeated applications with no visible improvement in the foliage.

🧪 Bracket a dosing with two measurements

Unlike nitrates, whose concentration rises on its own as long as the fish are being fed, the iron content depends entirely on what you add. It rises after each addition, then falls as plants absorb it and a portion precipitates. A single measurement therefore tells you little, whereas by bracketing each addition with two readings, one just before and another 24 to 48 hours after, you can directly gauge how much iron remained available. The rate at which the value declines over the following days then tells you the interval to observe between additions. Both of these markers depend on the pH of your water, the area under cultivation, and the species in place, which means that no general dosing guideline can replace them.

🌿 When iron levels are sufficient

A correct reading is just as useful as a low one, since it rules out iron as the cause and directs you elsewhere. Two causes tend to dominate when the level is adequate yet young leaves remain pale. A high pH blocks uptake long before the element disappears from the water, and a manganese deficiency produces a very similar leaf pattern. If the yellowing starts at the bottom of the plant instead, the tests to run are for magnesium or potassium, and the guide to deficiencies in aquaponics presents these patterns side by side.

Technical specifications

The essentials

Parameter measured: Dissolved iron, in mg/LThe reaction colours the iron that has stayed in solution; what has settled at the bottom of the tank is not counted
Colour chart range: 0.02 to 1.5 mg/LFirst field marked below 0.02, last field 1.5
The colour fields: 0,02 · 0,05 · 0,1 · 0,2 · 0,4 · 0,6 · 0,8 · 1,0 · 1,5Nine steps, packed closer together at the bottom of the scale, where the decision to add is made
Target values: 0.1 to 0.2 mg/L in a planted aquariumAround 2 mg/L in aquaponics, read from a sample diluted by half. Up to 0.6 mg/L in a heavily planted tank, and no more than 0.05 mg/L in seawater
Tests per kit: Approximately 50A single reagent bottle, 5 drops per measurement
Manufacturer's reference: JBL 2411600, PROAQUATEST rangeNot to be confused with the refill, reference 2411700

The procedure

Sample volume: 2 times 5 mlOne test tube receives the reagent, the other is left as it is and serves as the control
The steps: Rinse, draw the sample, add the reagent, mix, wait, read5 drops from a single bottle, held vertically, with a dry nozzle and no bubbles
Resting time: 10 minutesFull colour development. Reading earlier underestimates the value
Total duration: Approximately 12 minutesRinsing and reading included
Reading: In the notch of the comparator blockThe block slides along the colour chart until the two shades match.
A pitfall to know about: Rinse beforehand, several timesTraces of ammonium reagent in the test tube make the iron reading come out too high

Security and parcels

Ranking: WarningThe lower of the two threshold levels under CLP regulations
Main risks: Harmful if swallowed, skin allergyStatements H302, H317 and H319. Wear gloves if your skin is sensitive
Storage: Store dry, at room temperatureIn its original packaging, away from direct light
Parcel weight: 0.13 kgPackaging included

To budget for separately

Iron dosing: A chelate suited to your pHEDTA in acidic water, DTPA in neutral water, EDDHA in hard water
Reagent refill: Reagent only, ref. 2411700The glassware, comparator block and colour chart can be kept

10 further specifications are available in the detailed view.

In the box

1 Fe reagent dropper bottle
2 glass test tubes with screw caps
1 graduated syringe for drawing off 5 ml
1 grey comparator block with two compartments
1 colour chart with nine fields, from 0.02 to 1.5 mg/L
1 multilingual leaflet with the protocol in French

Reference, EAN code, number of measures, kit contents, protocol, interference with the ammonium reagent and hazard statements taken from the manufacturer's data sheet and instructions on 05/09/2026. The range and the nine steps are taken from the photograph of the colour chart supplied.

The iron test on its own, or a test kit that includes it

Iron is included in the 13-in-1 set but not in the 6-in-1.

Chlorosis always starts with the young leaves Iron does not move within the plant: the deficiency strikes new growth and leaves the veins green. If your older leaves are yellowing, look to nitrogen instead.

	Parameters covered (parameters)	Drop tests included (tests)	Iron Fe	pH, KH, nitrites and nitrates	GH, phosphates, copper, silicates, oxygen	Reagent bottles (bottles)	Glass test tubes	Laboratory comparator block	Thermometer	Reagent refill sold separately	Price
Recommended Iron test onlyYour choice	1 parameters	1 tests	Yes	No	No	1 bottles	2	Yes	No	Yes	$19.00
6-in-1 Aquarium Water Testing KitYour choice	6 parameters	5 tests	No	Yes	No	9 bottles	3	Yes	No	Yes	$59.00
13-in-1 water testing kit for aquariumsYour choice	12 parameters	13 tests	Yes	Yes	Yes	23 bottles	12	Yes	Yes	Yes	$138.00

Iron test onlyRecommended

What you're measuring

Parameters covered (parameters)1 parameters

Drop tests included (tests)1 tests

Iron FeYes

pH, KH, nitrites and nitratesNo

GH, phosphates, copper, silicates, oxygenNo

Equipment supplied

Reagent bottles (bottles)1 bottles

Glass test tubes2

Laboratory comparator blockYes

ThermometerNo

Budget

Reagent refill sold separatelyYes

6-in-1 Aquarium Water Testing Kit

What you're measuring

Parameters covered (parameters)6 parameters

Drop tests included (tests)5 tests

Iron FeNo

pH, KH, nitrites and nitratesYes

GH, phosphates, copper, silicates, oxygenNo

Equipment supplied

Reagent bottles (bottles)9 bottles

Glass test tubes3

Laboratory comparator blockYes

ThermometerNo

Budget

Reagent refill sold separatelyYes

13-in-1 water testing kit for aquariums

What you're measuring

Parameters covered (parameters)12 parameters

Drop tests included (tests)13 tests

Iron FeYes

pH, KH, nitrites and nitratesYes

GH, 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 noted from the three product pages on 05/09/2026.

Documents & manuals

Official manufacturer's instructions, French section

The full six-step protocol, the reference volume of 2 times 5 ml, the 5 drops of reagent, the 10 minutes' standing time, and the warning about test tubes shared with the ammonium test.

PDF · 2,9 Mo

Download

Estimate your
delivery time

0.12 kg parcel, dispatched within 48 hours by Colissimo or Chronopost home delivery, your choice at the time of payment. The reagent bottle is sent in its original cardboard box, with the glassware wedged in place. The exact shipping cost is shown in your basket.

Frequently asked questions

8 questions

6 key questions, 8 in the detailed view

What iron level should I aim for in the water?

My test shows 0 just after adding something, is that normal?

Yes, and it is in fact the most common case. Bare iron oxidises and precipitates within a few hours once the pH exceeds 6.5 in well-oxygenated water. A zero reading the next day therefore indicates iron that has dropped out of solution, not complete uptake by your plants.

This is the purpose of chelates: the molecule surrounding the iron keeps it dissolved, and each chelating agent has a pH ceiling beyond which it releases the iron. If you keep getting zero readings despite a chelated supply, change the form of the chelate rather than the dose.

Why do two iron tests not give the same figure?

The colour does not match any box on the colour chart, what happened?

Do you need to measure pH as well as iron?

Can I use the test tube from another test by the same brand?

How often should you test?

Can the reagent cause a skin allergy?

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Iron Fe water test in drops

The summary