Cardboard box for the PO4 Sensitive phosphate test, with 50 X TEST printed at the top

Contents of the PO4 phosphate kit: grey comparator block, measuring spoon, sampling syringe, glass test tubes, three reagent bottles and colour chart

Phosphate measurement in progress: test tube placed in the comparator block above the colour chart, with sampling syringe and reagent bottles alongside

The two reagents of the PO4 phosphate test, bottle 1 in powder form and bottle 2 as a dropper

Diagram of the phosphate test reading range, from 0.05 to 1.8 mg/L, with the lower threshold not consolidated at 0.02 mg/L and saturation beyond 1.8

Water phosphate PO4 drop test, 50 measurements

Name: Water phosphate PO4 drop test, 50 measurements
Brand: JBL
Price: 2000.0 RSD
Availability: InStock

2,000.00 RSD

This colorimetric test measures phosphate PO4 by drops, using a comparator block and a reference sample, for aquariums, ponds, and aquaponics. The scale starts at 0.05 mg/L, the range where the useful thresholds fall.

Phosphate feeds both plants and algae, and should be read alongside nitrate.

Format : Aquarium

Aquarium

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The summary

In the box: 3 reagent bottles, 2 glass test tubes, a syringe, a double measuring spoon, a comparator block and a colour chart.
What it measures: dissolved phosphate, from 0.05 to 1.8 mg/L, on a colour chart, with a blank sample that cancels out the natural tint of the water.
How long it takes: twelve minutes per test, including ten minutes of waiting time, with approximately 50 tests per kit.
Useful thresholds: 0.4 mg/L in a freshwater aquarium, 0.1 mg/L in a marine aquarium and in a garden pond.
How to choose: this is the parameter that sets the 6-in-1 kit apart from the 14-in-1.
What gets sent to you: a parcel weighing 0.12 kg, with reagents in their original box, available for collection point or home delivery.

Drop-based phosphate test, 50 measurements, for aquariums, ponds and aquaponics

Clean, unpolluted water contains around 0.01 mg/L of phosphate, whereas a heavily stocked tank can reach a hundred times that level without any visible sign. Phosphate does not cloud the water, has no smell, and causes no harm to fish at the concentrations found in an aquarium: it simply determines whether algae or your plants benefit from the nitrogen present. That is why it needs to be measured, and the Sensitive formulation in this kit reads from 0.05 mg/L.

🔬 Reading across two test tubes

The test uses two 10 ml test tubes: one receives the reagents while the other holds untreated water and serves as a reference sample in the grey comparator block. This setup compensates for the natural colour of the water and gives a reliable reading even in water darkened by peat filtration or a treatment, where a single test tube would return an artificially high value. The scale runs up to 1.8 mg/L, which comfortably covers the thresholds you need to monitor: 0.4 mg/L in a freshwater aquarium, 0.1 mg/L in a marine aquarium, and 0.1 mg/L in a garden pond.

🐟 Where does phosphate come from

The bulk of it comes from fish digestion and leftover food, as most people suspect. Two other sources, however, almost always go unnoticed. Some water companies add phosphates to the mains supply to reduce limescale and corrosion in the pipework, so your top-up water may already contain them straight from the tap. A garden pond also receives phosphates in spring, carried in by pollen and fertilisers from neighbouring land, which explains the algae blooms that appear even when you haven't changed anything about the way you manage it.

High phosphate, high nitrate

Both come from the same source: the tank receives more nutrients than it consumes.

High phosphate, low nitrate

The plants have used up the nitrogen and are struggling. Phosphate is building up without being used.

Low phosphate, algae present

Algae store it and keep growing after levels drop. Today's reading describes the water, not their reserves.

Low phosphate, slow-growing plants

In a heavily planted tank with few fish, it becomes a limiting factor and is dosed like a fertiliser.

Poorly dissolved powder throws everything off

Reagent 1 comes as a powder rather than a liquid, which changes how you handle it. Seal the test tube and shake until it has fully dissolved before adding the 10 drops of reagent 2, failing to do so will leave the colour pale and give you a reading that is too low. Use the sampling syringe provided to measure both 10 ml portions rather than estimating by eye, and allow the full 10 minutes to elapse, as the colour does not finish developing until that point.

Reading phosphate alongside nitrate

Neither figure alone can tell you whether you have an algae outbreak or a stalling crop, it is their ratio that matters. The nitrate test can be carried out on the same sample straight afterwards, adding just 10 minutes for a result that is twice as reliable. Pick up the reagent refill at the same time: only the bottles run out, while your glassware, sampling syringe, measure, comparator block and colour chart last from one purchase to the next.

🌱 Phosphorus in aquaponics

In aquaponics, phosphorus is one of the elements that water supplies most sparingly to plants. A coupled system's water contains roughly ten times less than a hydroponic solution, and a good proportion of what the feed provides is removed with the solid waste that the mechanical filter takes out of the circuit before it can mineralise. Your system may therefore show a comfortable nitrate reading and tomatoes that flower without setting fruit, the most telling sign of a deficiency. Visual symptoms often appear before any figure does, and the guide to deficiencies in aquaponics runs through each of them.

💧 Bringing a high value down

Start with the source rather than the remedy: cut back feeding, siphon the substrate where solid waste accumulates, then re-test after 48 hours before drawing any conclusions. A partial water change will achieve nothing if the top-up water already contains phosphate, a single test on tap water will tell you immediately. In a pond where the source cannot be eliminated, a phosphate treatment takes over by binding the dissolved fraction. Other approaches to tackling green water are covered in the article on pond algae in summer.

Technical specifications

The essentials

Parameter measured: Phosphate, expressed as PO4A nutrient for plants and algae alike, in fresh water, salt water and ponds
Measurement range: 0.05 to 1.8 mg/LThe Sensitive formulation reads the low end of the scale, right where the recommended thresholds fall.
Tests per kit: Around 50
Recommended thresholds: 0.4 mg/L in fresh water0.1 mg/L in a marine aquarium and in a garden pond
Method: Powder, drops, and comparator blockThe reference tube cancels out the natural colour of the water, including water coloured by peat.
Reference: JBL 2412700, PROAQUATEST rangeCode EAN 4014162241276

The procedure

Water volume: 2 x 10 mlOne test tube receives the reagents, the other remains with untreated water
Reagents to dose: 1 measure and 10 dropsSmall end of the double measure spoon for reagent 1, in powder form
The steps: Rinse, fill, dose, dissolve, wait, readIn that order. Fully dissolving the powder is the step people rush, and it determines the outcome.
Waiting time: 10 minutesDuration of the complete colour change. Reading too early gives a low value
Total duration: Approximately 12 minutesHandling included
Reading: In the block's notchSlide the block along the colour chart until the two shades match

Security and parcels

Ranking: DangerTwo of the three bottles are classified. Declared components: hydrochloric acid and sulphuric acid
Main risks: Burns, eye injuriesH314 and H318 statements. H302 if swallowed, H335 for the respiratory tract
Precautions: Sink, ventilated room, out of reachNever smell a bottle or a test tube, and empty the treated test tube down the sink.
Parcel weight: 0,12 kgPackaging included

To budget for separately

Reagent refill: Reagents only, ref. 2412800The glassware, the sampling syringe, the measuring spoon, the comparator block, and the colour chart are all reusable.
To read alongside: NitrateIt is the rarer of the two nutrients that limits growth: phosphate alone is not enough

10 further specifications are available in the detailed view.

In the box

3 reagent bottles, including 2 of reagent 2
2 glass test tubes with screw caps
1 graduated sampling syringe
1 double measuring spoon, large and small end
1 grey comparator block with reading notch
1 colour chart and 1 multilingual instruction leaflet, French included

Reference, EAN code, kit contents, number of tests, protocol, thresholds by application, and hazard statements taken from the product datasheet and manufacturer's instructions on 19/09/2026. The range of 0.05 to 1.8 mg/L comes from the manufacturer's text, reproduced by retailer listings. The tenfold difference in phosphorus between a coupled aquaponics system and a hydroponic solution is drawn from scientific literature on the nutrient cycle in aquaponics.

The phosphate on its own, or the rest of the water with it?

Same drop reagents, same comparator block, same manufacturer. What differs is the number of parameters the kit covers, and phosphate is only present in the larger of the two.

Phosphate on its own, or a test kit? Two questions about your setup, and the table highlights itself.

	Parameters covered (parameters)	Drop tests included (tests)	Phosphates PO4	Nitrates, ammonium, nitrites, pH and carbonate hardness	Iron, copper, oxygen and silicates	Glass test tubes	Laboratory comparator block	Thermometer	Reagent refill sold separately	Price
Recommended PO4 phosphate test onlyYour choice	1 parameters	1 tests	Yes	No	No	2	Yes	No	Yes	2,000.00 RSD
6-in-1 Aquarium Water Testing KitYour choice	6 parameters	5 tests	No	Yes	No	3	Yes	No	Yes	5,100.00 RSD
14-in-1 water analysis kit for aquariumYour choice	14 parameters	13 tests	Yes	Yes	Yes	12	Yes	Yes	Yes	10,700.00 RSD

PO4 phosphate test onlyRecommended

What the kit covers

Parameters covered (parameters)1 parameters

Drop tests included (tests)1 tests

Phosphates PO4Yes

Nitrates, ammonium, nitrites, pH and carbonate hardnessNo

Iron, copper, oxygen and silicatesNo

Equipment supplied

Glass test tubes2

Laboratory comparator blockYes

ThermometerNo

What needs replacing

Reagent refill sold separatelyYes

6-in-1 Aquarium Water Testing Kit

What the kit covers

Parameters covered (parameters)6 parameters

Drop tests included (tests)5 tests

Phosphates PO4No

Nitrates, ammonium, nitrites, pH and carbonate hardnessYes

Iron, copper, oxygen and silicatesNo

Equipment supplied

Glass test tubes3

Laboratory comparator blockYes

ThermometerNo

What needs replacing

Reagent refill sold separatelyYes

14-in-1 water analysis kit for aquarium

What the kit covers

Parameters covered (parameters)14 parameters

Drop tests included (tests)13 tests

Phosphates PO4Yes

Nitrates, ammonium, nitrites, pH and carbonate hardnessYes

Iron, copper, oxygen and silicatesYes

Equipment supplied

Glass test tubes12

Laboratory comparator blockYes

ThermometerYes

What needs replacing

Reagent refill sold separatelyYes

Parameters covered, equipment provided and kit contents taken from the three product pages on 05/09/2026. Pages compared: the 6-in-1 kit and the 14-in-1 kit.

Documents & manuals

Official manufacturer's instructions, in French

Six-step protocol, dosing for both reagents, recommended thresholds in fresh water, salt water and ponds, and sources of phosphate in the water.

PDF · 1,6 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, powder and drops kept separate. The exact cost is shown in your basket.

Frequently asked questions

8 questions

6 key questions, 8 in the detailed view

My phosphates are at zero and I still have algae – why?

Because algae have already built up reserves. They store considerable quantities of phosphate and continue to proliferate for some time after levels drop. A zero reading today describes the water, not the algae.

The second reason is more structural. Algae and plants have both adapted to natural concentrations, around 0.01 mg/L, and get by on very little. Starving everything equally does not penalise both sides in the same way: crops stop growing before algae do. The useful lever is knowing whether nitrate or phosphate runs out first in your system.

What phosphate level should be maintained to prevent algae?

Where do phosphates in an aquarium come from?

They come from five sources, in order of importance:

the digestive activity of the fish, the primary source;
uneaten food residues;
tap water, when the water company adds phosphates to it;
spring pollen, on a garden pond;
fertiliser run-off from neighbouring gardens reaching the pond.

Natural fresh water contains around 0.01 mg/L of phosphate. A heavily stocked tank can contain a hundred times more.

Do water companies add phosphates to tap water?

Where do you start to bring phosphate levels down?

Adjust the ration. Feeding in line with your fish's actual needs comes before any product.
Siphon out the deposits. Whatever settles on the bottom keeps releasing phosphate.
Put plants to work. They are the only consumers that require no consumables.
Fix the rest with a phosphate remover, when the source cannot be reduced quickly enough.
Re-measure nitrate at the same time. Dropping below the nitrate level, or the reverse, does not produce the same result on algae.

Should you aim for zero phosphate?

What does Sensitive on the box mean?

The term means the formulation is calibrated for low concentrations. This comes down to three points:

What changes	Value	What it gives you
First readable step	0.05 mg/L	Distinguishes between 0.1 and 0.4, which are the two recommended thresholds
Upper limit of the range	1.8 mg/L	A heavily loaded pond will saturate the test: dilute the sample before testing
Volume sampled	10 ml	Twice as much as an ammonium test, which improves reading accuracy

Do the reagents contain acid?

Yes: the two declared components are both strong mineral acids, hydrochloric acid and sulphuric acid. They account for the Danger label and the H314 and H318 statements, covering severe skin burns and serious eye damage.

The H335 statement is the only one of its kind in this range: it flags possible irritation of the respiratory tract, and it changes one habit — that of sniffing a bottle to check something. Work over a sink, in a well-ventilated room, replace the caps between drops, and empty the treated test tube down the sink rather than into the tank. The H302 statement is a further reminder that a child-resistant cap is no substitute for a locked cupboard kept out of reach.

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Water phosphate PO4 drop test, 50 measurements

The summary