Soluble potassium sulphate
Regular price
$8.00
Regular price
Sale price
$8.00
Unit price
/
per
| Format | Price | Price per kg | vs 500 g |
|---|---|---|---|
| 500 g | $8.00 | $16.00 | — |
| 1 Kg | $12.00 | $12.00 | −25 % |
| 2.5 Kg | $19.00 | $7.60 | −53 % |
| 5 Kg | $31.00 | $6.20 | −61 % |
$2.66 × 3 with no fees
Klarna.
This soluble potassium sulphate corrects potassium levels in aquaponic and hydroponic systems, with no chlorine, no nitrogen, and no impact on pH. It contains 52.5% K2O and dissolves in warm water: 23 g per 1,000 litres raises potassium by approximately 10 mg per litre.
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The summary
- What you receive: soluble potassium sulphate at 52.5% K2O and 45% SO3, in your chosen size.
- Sulphate or bicarbonate: sulphate leaves the pH unchanged, bicarbonate raises it at the same time as boosting potassium.
- How much to dissolve: 23 g in 1,000 litres raises potassium by approximately 10 mg per litre.
- Signs of deficiency: yellow then brown edges on older leaves, and poor fruit set.
Potassium and sulphur, chlorine- and nitrogen-free, to correct a deficiency in aquaponics
Soluble potassium sulphate, also known as sulphate of potash or SOP, supplies potassium and sulphur to crops without any chlorine or nitrogen. It contains 52.5% K2O, equivalent to 43.6% potassium, as well as 45% SO3, and dissolves almost residue-free in lukewarm water. In aquaponics, it corrects potassium levels when your water pH is already within range, without affecting the nitrogen produced by your fish or the alkalinity.
🐟 Potassium in aquaponics
Fish do not need as much potassium as plants, and their feed provides far too little to support a crop of fruiting vegetables. Potassium is therefore, along with iron and calcium, one of the most common deficiencies in an aquaponic system, and it is felt most acutely at flowering and fruit set, when the demand from your plants increases. Two families of products address this: alkaline forms, such as potassium bicarbonate, which also raise pH, and sulphate, which adds no carbonate and is the choice when pH does not need correcting.
Potassium sulphate
It supplies potassium and sulphur without affecting alkalinity. This is the form to choose when the pH stays within range.
Potassium bicarbonate
It supplies potassium and carbonate, which raises the KH and pH. It suits systems where pH drops with nitrification.
Potassium chloride
Cheaper, it introduces chlorine that accumulates in a closed circuit. It has no place in a system with fish.
🍂 Older leaves first
Potassium is mobile within the plant, which draws it from older leaves to supply young growth. The first signs therefore appear at the base of the stems: the edges of older leaves turn yellow, then brown and dry out, while the centre of the leaf blade remains green. Growth slows, stems lose their rigidity, and on tomatoes or peppers, flowers set poorly and fruit development is limited. The guide on identifying deficiencies compares these signs with those of magnesium deficiency, which look similar in the early stages.
Measure potassium before dosing
A drop-based potassium test gives you the actual level in your water, and it's the gap between that reading and your target that determines how much sulphate to dissolve. Without a measurement, you're correcting blind, particularly risky since potassium deficiency symptoms closely resemble those of magnesium. Weigh out the dose on a gram-accurate scale, because 23 g per 1,000 litres simply cannot be measured with a spoon.
An excess of potassium inhibits magnesium uptake
Potassium competes with calcium and magnesium during root uptake. An overly generous application corrects one deficiency while triggering another, often visible as yellowing between the veins of older leaves. Apply in split doses guided by measurement, and check magnesium levels if you are correcting potassium over several consecutive weeks.
⚖️ Measuring by the mark
One gram of product delivers 0.44 g of potassium. In 1,000 litres, 23 g therefore raises the potassium concentration by approximately 10 mg per litre and adds 12 mg per litre of sulphate. Dissolve the measured dose in a bucket of warm water, pour it into a well-circulated area with the pump running, then re-test the following day. Sulphate accumulates for as long as you do not change the water: a series of additions remains within the thresholds recommended for aquatic life, and regular partial water changes prevent it from building up month after month. Other supplements used in the system are covered in the article on fertilisers in aquaponics.
Technical specifications
Composition
- Formula
- K2SO4Also known as sulphate of potash or SOP, CAS number 7778-80-5.
- Potassium
- 52.5 % of K2OThat is 43.6% potassium: one gram provides 0.44 g.
- Sulphur
- 45 % SO3That is 18% sulphur, in the form of sulphate.
- Chloride
- 0.15 %A negligible content, unlike potassium chloride.
- Insoluble
- 0.05 %Virtually no sediment at the bottom of the mixing bucket.
- Solubility
- Approximately 100 g/L at 20 °CDissolve the dose in lukewarm water before pouring it in.
Use in aquaponics
- Correction dose
- 23 g per 1,000 LIt raises potassium by approximately 10 mg per litre.
- Sulphate supplied
- 12 mg/L per doseIt accumulates as long as the water is not refreshed.
- When to choose it
- pH already within its rangeIf your pH drops, potassium bicarbonate corrects both issues at the same time.
- Method
- Dissolve, then pourIn an agitated zone, with the pump running.
Framework and storage
- Organic farming
- Approved for organic use (UAB)European Regulations 2018/848 and 2021/1165.
- Origin
- Germany
- Storage
- Store dry, resealable bagThe powder clumps in damp conditions without losing its potency.
- Incompatibility
- Concentrated calciumMixed in concentrate, sulphate and calcium form gypsum: prepare a separate stock solution for each.
To budget for separately
- Potassium test
- Potassium drop test
- Gram-accurate scales
- Weighed to the nearest gram
8 further specifications are available in the detailed view.
In the box
- 1 sachet of soluble potassium sulphate, in the chosen size
Contents, chloride, insolubles, solubility, and organic certification status: technical data sheet for K+S soluble potassium sulphate and the distributor's documentation, recorded on 01/10/2026. Sulphate thresholds for aquatic life: British Columbia guidelines, 2013. Doses calculated on 43.6% potassium, annual consumption based on the application rate published by an aquaponic greenhouse manufacturer.
Sulphate, bicarbonate, or potassium and magnesium fertiliser
All three supply potassium. What sets them apart is their effect on water pH and the additional element each one provides.
The same potassium, three different effects on your water
The right product depends on how your pH is moving and the condition of your older leaves. Two observations are enough to decide.
| Potassium, as K2O (%) | Adds sulphur | Provides magnesium | Raises pH and KH | Shape | Price | |
|---|---|---|---|---|---|---|
| Recommended Soluble potassium sulphateYour choice | 52,5 % | Yes | No | No | soluble powder | $12.00 |
| Potassium BicarbonateYour choice | 47 % | No | No | Yes | powder | $28.00 |
| Potassium, magnesium and sulphur fertiliser in granule formYour choice | 30 % | Yes | Yes | No | granules | $11.00 |
Soluble potassium sulphateRecommended
What it provides
Potassium, as K2O (%)52,5 %
Adds sulphurYes
Provides magnesiumNo
Effect on water
Raises pH and KHNo
Shapesoluble powder
Potassium Bicarbonate
What it provides
Potassium, as K2O (%)47 %
Adds sulphurNo
Provides magnesiumNo
Effect on water
Raises pH and KHYes
Shapepowder
Potassium, magnesium and sulphur fertiliser in granule form
What it provides
Potassium, as K2O (%)30 %
Adds sulphurYes
Provides magnesiumYes
Effect on water
Raises pH and KHNo
Shapegranules
Values recorded on 01/10/2026 from the product sheets for all three products and from the technical data sheet for soluble potassium sulphate. Bicarbonate content calculated from its formula KHCO3.
Help choosing
Which potassium for your system
Documents & manuals
Technical data sheet soluSOP 52 Organic
It guarantees 52.5% K2O and 45% SO3, and specifies chloride, insolubles, pH, and solubility from 10% to 20 °C.
Document not showing? Some publishers block display inside a frame, so open it in a tab.
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A robust powder, dispatched by tracked parcel from France. Exact shipping costs and final delivery times are displayed at checkout once your address has been entered. Outside the European Union, import duties and taxes remain the responsibility of the recipient. Delivery times run from the date of dispatch, excluding public holidays.
Frequently asked questions
6 questions
6 key questions
How much potassium sulphate for your water volume
Enter the volume of water actually circulating in your system, including grow beds and reservoir. The calculation is based on a potassium content of 43.6% in the product.
L
50 L10000 L
0g
to raise the potassium level by approximately 10 mg per litre.
To raise potassium by approximately 40 mg per litre, in several applications
0 g
Calculation based on 43.6% potassium. Every 10 mg of potassium added introduces approximately 12 mg of sulphate per litre. Adjust on the basis of a potassium measurement taken before and after the application.
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Guide
Which fertiliser should you use in aquaponics?
It highlights what fish cover poorly — potassium above all — and how to supplement it without upsetting the system.
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Diagnosis
Identifying deficiencies in aquaponics
Its table distinguishes potassium deficiency from magnesium deficiency, whose early signs look very similar.
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Understanding
Plant deficiencies in aquaponics
The article explains why iron, potassium and calcium are the three elements to monitor as a priority.
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Technique
Regulating pH in an aquaponics system
Your pH determines the form of potassium to apply, and this article explains how to keep it within its range.
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Crops
Growing tomatoes in aquaponics
Tomato is one of the crops with the highest potassium demand at fruit set.
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Crops
Growing peppers in aquaponics
This guide details the conditions for growing peppers, including nutrition during the fruiting stage.
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