Blister pack of the JBL PROAQUATEST PO4 Sensitive refill, one powder reagent and two bottles of reagent 2

Reagent refill for phosphate PO4 test

Name: Reagent refill for phosphate PO4 test
Brand: Hardy Dewerse
SKU: J2412800
Price: 10.18 USD
Availability: InStock

$10.18

$3.39 × 3 with no fees Klarna.

These three bottles, including two of reagent 2, are the reagents for the phosphate test, for approximately 50 measurements.

This formulation measures the lower end of the scale, from 0.05 to 1.8 mg/L, where the recommended thresholds lie. The glassware, syringe, measuring spoon, comparator block, and colour chart from your kit remain in use.

Ref. J2412800·Reagent refill

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The summary

What it measures: dissolved phosphate, a nutrient for both plants and algae.
What the box contains: 3 bottles, including 2 of reagent 2.
The reading range: from 0.05 to 1.8 mg/L, a formulation sensitive at the lower end of the scale.
The threshold to maintain: 0.4 mg/L in freshwater, 0.1 mg/L in a garden pond.
What to read alongside it: the nitrate level of the same water, on the same day.
Refill or complete kit: the refill is sufficient if you have kept the double measure and colour chart from the original kit.

The three reagents for the phosphate test, approximately 50 measurements, from 0.05 mg/L.

In a tank, phosphate comes mainly from fish waste and leftover food, and some water companies add it to tap water to protect pipework. These three bottles, one powder reagent and two bottles of reagent 2, are the reagents only for the sensitive phosphate test, for approximately 50 measurements.

This test detects low concentrations, allowing you to spot a rise in phosphate before an algae bloom takes hold. Unpolluted natural water contains around 0.01 mg/L, whereas a heavily stocked tank can contain a hundred times that amount. The benchmarks are to stay below 0.4 mg/L in freshwater and below 0.1 mg/L in a marine aquarium or garden pond, three thresholds that fall in the lower end of the colour scale, which runs from 0.05 to 1.8 mg/L.

🥄 The small end of the measuring scoop

Fill two 10 ml test tubes, then add a level micro-scoop of powder to one of them, using the narrow end of the double-ended measure. Stopper the test tube and shake until the powder has dissolved completely, then add 10 drops of reagent 2, mix and leave to stand for 10 minutes. Read the result in the comparator block, alongside the untreated test tube.

A tube that remains colourless indicates the wrong end

If your test tube remains clear or barely yellow when the water contains phosphate, you have most likely used the large end of the measuring spoon. The small end is at the handle end of the spoon and should be filled level. The same symptom appears with expired reagents, or those opened more than 9 to 12 months ago.

🐟 Fish ration and growing area

In aquaponics, your plants consume a portion of the phosphate introduced through feed, so the reading reflects the balance between fish rations and the growing area. A figure that rises week after week points first to the feeding rate. Polyphosphates sometimes added to mains water do not show up straight away: the test only detects them once they have hydrolysed into orthophosphates, a slow process that depends on pH. The article on cloudy water in aquaponics separates the causes that look the same to the naked eye.

Test nitrate too when the pond turns green

Pick up the nitrate test refill at the same time if your tank or pond is turning green. Algae develop when nitrate and phosphate are both present, and taking both readings on the same day tells you which one to address first. In a garden pond, the anti-phosphate treatment is the next step if the reading exceeds 0.1 mg/L.

📌 Shelf life after opening

Only reagent 2 is classified, carrying the Danger signal word and the hazard statements H314, H318, H302, and H335, as it contains hydrogen chloride. Store the capped bottles in a dry place, at room temperature, and in their original packaging, and only open the second bottle of reagent 2 once the first is empty. Once opened, these reagents keep for 9 to 12 months: note the opening date on the box so you know when your kit needs replacing, even if liquid remains.

Technical specifications

What the refill contains

Contents: 3 bottles, including 2 of reagent 2One powder reagent and two bottles of liquid reagent
Measurements: Approximately 50One small measure of powder and 10 drops per reading

Reading phosphate

Measurement range: 0.05 to 1.8 mg/LA sensitive formulation that reads the low end of the scale where the thresholds fall.
Recommended thresholds: 0.4 mg/L in freshwater0.1 mg/L in a marine aquarium and in a garden pond

Reference and safety

Manufacturer's reference: JBL 2412800, PROAQUATEST rangeNot to be confused with 2412700, which is the complete kit
Hazard classification: Danger, reagent 2H314, H318, H302 and H335 labelling. Hydrogen chloride declared

To budget for separately

Glassware, syringe and measure: Those from the phosphate testTwo 10 ml test tubes, and the small end of the double-ended measuring scoop for the powder
Comparator block and colour chart: Those from the phosphate testThe block slides along the colour chart until the two shades match.

In the box

3 bottles of reagents, including 2 of reagent 2

Reference, EAN code, contents, protocol, number of tests and hazard statements taken from the JBL data sheet and instructions on 07/10/2026. Storage of 9 to 12 months after opening: JBL FAQ. The measurement range corresponds to the test colour chart.

The three bottles, or the phosphate test kit?

The same sensitive formulation and the same test count are found in both. What separates the two kits is the measuring spoon and the reading optics.

The useful thresholds fall within the first third of the colour chart. The freshwater threshold is 0.4 mg/L, and 0.1 mg/L for a pond. Accurate dosing and the ability to read low colour values clearly are therefore essential.

	Reagent bottles (bottles)	Possible readings (measurements)	Screw-top glass test tubes	Graduated sampling syringe	Double measure for powder	Grey comparator block	Colour comparison chart	Price
Recommended Reagent refill for phosphate PO4 testYour choice	3 bottles	50 measurements	No	No	No	No	No	$10.18
Water phosphate PO4 drop test, 50 measurementsYour choice	3 bottles	50 measurements	Yes	Yes	Yes	Yes	Yes	$18.19

Reagent refill for phosphate PO4 testRecommended

What gets used up

Reagent bottles (bottles)3 bottles

Possible readings (measurements)50 measurements

What keeps well

Screw-top glass test tubesNo

Graduated sampling syringeNo

Double measure for powderNo

Grey comparator blockNo

Colour comparison chartNo

Budget

Water phosphate PO4 drop test, 50 measurements

What gets used up

Reagent bottles (bottles)3 bottles

Possible readings (measurements)50 measurements

What keeps well

Screw-top glass test tubesYes

Graduated sampling syringeYes

Double measure for powderYes

Grey comparator blockYes

Colour comparison chartYes

Budget

Contents of both columns taken from the supplier's data sheet and instruction leaflet, on 05/09/2026.

Estimate your
delivery time

Parcel weight 0.08 kg, dispatched to a collection point or to your home address — your choice at checkout. All three bottles are sent in their original packaging. The exact shipping cost is shown in the basket.

Frequently asked questions

6 questions

6 key questions

Why are there two bottles of reagent 2?

Does phosphate alone explain an algae bloom?

No, never on its own. It is the scarcer of the two nutrients that limits growth, in algae as much as in plants. High phosphate combined with rock-bottom nitrate does not produce the same outcome as high phosphate with high nitrate.

Read both in the same water sample, on the same day, using the nitrate test. It is the pair of values together that guides the correction, not either one in isolation.

Why must the powder be completely dissolved?

A granule left at the bottom has not reacted, and the resulting colour will be paler than the true reading.

On a test where the relevant thresholds are measured to the nearest tenth of a milligram, that discrepancy is enough to make a dirty water sample read as clean. Stopper the test tube, shake until the liquid is clear, and check the bottom against the light before starting the 10-minute wait.

What level should I target for my setup?

Your setup	Recommended threshold
Freshwater aquarium	0.4 mg/L
Marine aquarium	0.1 mg/L
Garden pond	0.1 mg/L

All three thresholds fall within the first third of the reading range, which is why this sensitive formulation exists.

Where does phosphate come from in an aquaponic system?

Can this test be read in coloured water?

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Reagent refill for phosphate PO4 test

The summary