Potassium Bicarbonate

$17.65

Weight	Prix	Prix au kg	vs 1 kg
1 kg	$17.65	$17.65	—
2 kg	$31.39	$15.70	−11 %

Potassium bicarbonate (KHCO₃) corrects the acidification that nitrification continuously produces in an aquaponic system. It raises the pH, rebuilds the KH that prevents it from dropping again, and releases potassium that plants can absorb directly.

Unlike sodium bicarbonate, it introduces no sodium, which accumulates in a closed circuit without being consumed. A bicarbonate solution caps out at around pH 8.3: even if overdosed, it cannot cause the alkaline shock that potash can.

Weight : 1 kg

7/7 customer service by e-mail

Payment in instalments, free of charge

The summary

How much to add: approximately 36 g per cubic metre of water to raise KH by one degree. The calculator works out the amount for your volume.
What it does to the water: one degree of KH gained, and 14 mg/L of potassium delivered to the plants in the process.
Potassium, sodium or calcium: sodium bicarbonate adds 8.2 mg/L of sodium per degree corrected, and that sodium never leaves.
Safe for fish: no measurable effect on growth up to 600 mg/L of potassium, well beyond any useful dosing level.
What is in the bag: potassium bicarbonate powder, 1 kg or 2 kg, and nothing else. No measuring scoop, no test kit.
Shipping: standard parcel of 1 to 2 kg, allow 3 to 5 working days within mainland France.

Raises pH, restores KH and adds potassium, without introducing sodium.

In an aquaponic system, pH does not drift at random: it drops. The bacteria in the biofilter oxidise the fish's ammonia into nitrate and release H+ ions in the process, gradually consuming the water's alkaline reserve day after day. This is the mechanism described in our article on the nitrogen cycle in aquaponics. Potassium bicarbonate is the product that replenishes this reserve, and in doing so it supplies the nutrient that plants most commonly lack.

How much to use, and what effect to expect

The calculation is straightforward. One German KH degree equals 17.85 mg/L of calcium carbonate equivalent. With a molar mass of 100.12 g/mol and one bicarbonate ion per molecule, you therefore need 35.7 mg of potassium bicarbonate per litre to gain one degree, or roughly 36 g per cubic metre. Two independent field references give 36 and 39 g: start with the lower value, measure the following day, then adjust. The dosage calculator works out the figures for your exact volume, and a KH test tells you where you stand before adding anything.

Why it cannot cause a pH shock

A bicarbonate solution stabilises at around pH 8.2, measured between 8.13 and 8.27 depending on concentration. This is not a setting, it is an inherent property of the bicarbonate ion, which sits midway between the two acidity constants of carbonic acid. The practical consequence: regardless of how much you add, the product cannot push the water beyond this value. Potash, on the other hand, rises to pH 13 and burns whatever it contacts. That is the entire difference between correcting and risking.

Potassium rather than sodium: what the calculation shows

Sodium bicarbonate raises KH for less money, and that is the only point in its favour in aquaponics. Each degree of KH corrected with it deposits 8.2 mg of sodium per litre. Plants consume virtually none of it and the biofilter does not remove it: in a closed circuit, it accumulates. Twenty-two one-degree corrections, less than two years at a rate of one per month with no water changes, is enough to reach 184 mg/L, the threshold at which lettuce, cucumber and pepper begin to suffer, according to Wageningen research on soilless cultivation. The FAO is even more direct: sodium bicarbonate should never be used in aquaponics.

Potassium bicarbonate

36 g per cubic metre for one degree of KH, and 14 mg/L of potassium delivered to the plants. No sodium. It is the only one of the four that corrects the pH and feeds at the same time.

Sodium bicarbonate

30 g per cubic metre for the same degree, slightly cheaper, but 8.2 mg/L of sodium each time. Reserve for tanks without plants.

Calcium carbonate

It supplies calcium, which is also useful. However, it only dissolves to 13 mg/L in neutral water: it acts slowly, only while the water is acidic, and stops on its own.

Potassium hydroxide

Same potassium input, but this is a strong, corrosive base that brings pH up to 13. It requires precautions that bicarbonate does not.

The other half of the benefit is nutritional. Potassium is the nutrient most often deficient in aquaponics, because fish feed is formulated for fish, not tomatoes. Potassium bicarbonate contains 39% of its mass as potassium, and each degree of KH corrected releases 14 mg/L into the water. Yellow then brown leaf edges on older leaves, fruit that stays small, soft stems: our guide to plant deficiencies in aquaponics covers the symptoms in detail, and the rest of the range can be found in the fertilisers and mineral supplements collection.

When to add it, and how often

Three signs are enough to warrant an addition: a pH persistently below 6.5, a KH below 3 or 4 degrees, or a pH that drops again a few days after each correction. This last case is the most telling: it means the buffer reserve is exhausted and you are treating the symptom rather than the cause. Our article on pH regulation in aquaponics covers the full approach. Aim for 4 to 8 degrees of KH and a pH between 6.5 and 7, the usual compromise between what the bacteria, plants, and fish prefer.

Common mistakes to avoid

The first mistake is pouring the dry powder directly into the pond: it concentrates locally before diluting. Always pre-dissolve in a bucket of warm water. The second is trying to correct everything in one go: one to two degrees of KH per day at most, with 48 hours between applications, to allow the fish and bacteria to adjust. The third is dosing without measuring: without a pH test or KH test before and 24 hours after, you are flying blind. The fourth is leaving the bag open: the powder is hygroscopic and will clump.

The product keeps indefinitely as long as it remains dry, stored in an airtight container at between 15 and 25 degrees. It only begins to decompose at 292 degrees, a temperature no storage room will ever reach. If it has caked, it has absorbed moisture from the air: it remains chemically identical and dissolves just as well, simply crumble it before weighing.

Technical specifications

Dosage and effect on water

Dose to raise the KH by one degree: 36 g per cubic metreStoichiometric calculation giving 35.7 mg/L, rounded. One field reference goes up to 39 g: start low, then adjust after measuring.
Potassium supplied: 14 mg/L per corrected degreePotassium bicarbonate contains 39% potassium by mass, released entirely into the water.
Maximum achievable pH: Approximately 8.3, regardless of the doseA property of the bicarbonate ion, measured between 8.13 and 8.27 depending on concentration. Overdosing cannot cause an alkaline shock.
KH target in aquaponics: 4 to 8 degreesBelow 4, the buffer reserve is too thin and pH fluctuates from one day to the next.
pH target in aquaponics: 6.5 to 7.0A compromise between nitrifying bacteria, which prefer more alkaline conditions, and nutrient availability, which improves at lower pH.
Maximum rise per day: 1 to 2 degrees of KHBeyond this point, fish and bacterial colonies do not have time to adapt.
Interval between applications: 48 hoursA delay retained by field protocols, allowing time for the water to homogenise and for the reading to become reliable again.
Dissolving: Pre-dissolve in lukewarm waterNever apply as dry powder directly into the pond, and never onto the grow medium or roots.

The compound

Chemical formula: KHCO₃One potassium ion and one bicarbonate ion — two ions naturally present in mineral waters.
Molar mass: 100.12 g/molConsistent value across two independent chemical databases.
Potassium content: 39% of the mass39.05% by calculation from atomic masses; 39.06% as reported by a field source.
Sodium added: NoneThis is the fundamental difference from sodium bicarbonate, which deposits 8.2 mg/L per degree corrected.
Solubility in water: 224 g/L at 20 degreesLower value retained. Some sources give up to 337 g/L. In either case, one kilogram dissolves in less than five litres.
pH of a solution: 8.13 to 8.27Measured on solutions of 1 to 100 mmol/L. The theoretical value is 8.34.
Decomposition temperature: 292 degreesIt then converts to potassium carbonate, releasing carbon dioxide and water.
CAS number: 298-14-6Also listed as food additive E501(ii), used as an acidity regulator.

Safe for living organisms

Measured Effect on Fish: None up to 600 mg/L of potassiumGrowth of the African catfish unchanged. Behavioural changes appear at this concentration; growth only declines above 670 mg/L.
Recommended range for ponds: 200 to 400 mg/L of potassiumThe range proposed by the same study to balance plant requirements and fish welfare.
Nutritional Target for Plants: 40 to 70 mg/L of potassiumAn approximate figure from a single source, to be confirmed by a potassium test on your own water.
Margin between target and first effect: Factor 8 to 15Ratio between the upper nutritional target and the lowest concentration at which an effect on fish was observed.
Effect on the biofilter: FavourableNitrifying bacteria consume alkalinity: replenishing the KH supports their activity rather than hindering it.
Phytosanitary use of the compound: Fungicide approved for organic usePotassium hydrogen carbonate is approved as an active substance against powdery mildew and scab in organic farming.
Handling: Gloves and a ventilated areaThe concentrated powder is irritating to the eyes and mucous membranes. Rinse thoroughly with clean water if contact occurs.
Classification: Not classified as hazardousThis does not remove the need to avoid inhaling dust when preparing large quantities.

Packaging and storage

Available pack sizes: 1 kg and 2 kgThe price per kilo drops on the 2 kg pack.
Shape: White crystalline powderOdourless, with no colourants or additives.
Behaviour in air: HygroscopicAbsorbs ambient moisture and clumps. The product remains usable — simply break it up before weighing.
Storage: Airtight container, kept dryTwo independent chemical sources recommend keeping the container tightly closed in a cool, dry place.
Storage temperature: 15 to 25 degreesChemical data sheet recommendation. Avoid temperature fluctuations, which cause moisture to condense inside the sachet.
Shelf life: No Practical Limit When DryThe compound only decomposes above 292 degrees. Moisture is the only concern, and it does not alter the composition.
Corrections covered by 1 kg: 28 degrees of KH in 1,000 LAt 36 g per degree per cubic metre. Divide by the actual volume of your system.
Corrections covered by 2 kg: 56 degrees of KH in 1,000 LSame calculation basis. On a 3,000 L system, that equates to approximately 18 one-degree corrections.

24 further specifications are available in the detailed view.

In the box

1 sachet of powdered potassium bicarbonate, 1 kg or 2 kg depending on the variant chosen
The sachet contains potassium bicarbonate only: no additives, no colourants, no anti-caking agent.
No dispenser, measuring spoon, or printed instructions are included: have a kitchen scale accurate to the gram to hand.
The pH and KH test kits are not included; they are sold separately and remain essential for accurate dosing.
No airtight storage container is included: one should be provided if you do not already have one, as the powder is hygroscopic.

The dose of 36 g per cubic metre per degree of KH is the stoichiometric calculation, corroborated by two independent sources: one degree equals 17.85 mg/L of calcium carbonate equivalent, with a molar mass of 100.12 g/mol. A French field reference gives 39 g, roughly a 9% difference: the range of 36 to 39 is the honest reading, and only a measurement on your own water will give a definitive answer. The physicochemical properties come from chemical databases; solubility varies between 224 and 337 g/L depending on the source, so we use the lower figure. The thresholds for fish come from a published study on African catfish and cannot be applied directly to all species; the nutritional target of 40 to 70 mg/L is based on a single source and should be treated as an order of magnitude.

Potassium bicarbonate, sodium bicarbonate or calcium carbonate

All three raise the KH. What sets them apart is what they leave behind in the water once the job is done, and the rate at which they do it.

Can't decide between the three? Three questions about your problem, your water circuit and your deficiencies, and we highlight the product made for you.

	Dose to raise KH by one degree in 1 cubic metre (g)	Solubility in water at 20 degrees (g per litre)	Dissolves completely at the working dose	Effect achieved in under an hour	Nutrient delivered per degree of KH corrected (mg per litre)	The nutrient supplied feeds the plants	Sodium added per degree of KH corrected (mg per litre)	Suitable for a closed circuit with little water renewal	Corrects a potassium deficiency	Corrects a calcium deficiency	Not recommended in aquaponics by the FAO	Usable alone as the sole KH corrector
Recommended Potassium bicarbonateYour choice	36 g	224 g per litre	yes	yes	14 mg per litre	yes	0 mg per litre	yes	yes	no	no	yes
Sodium bicarbonateYour choice	30 g	96 g per litre	yes	yes	0 mg per litre	no	8,2 mg per litre	no	no	no	yes	no
Calcium carbonateYour choice	18 g	0,013 g per litre	no	no	7,1 mg per litre	yes	0 mg per litre	yes	no	yes	no	no

Potassium bicarbonateRecommended

Effect on KH

Dose to raise KH by one degree in 1 cubic metre (g)36 g

Solubility in water at 20 degrees (g per litre)224 g per litre

Dissolves completely at the working doseyes

Effect achieved in under an houryes

What goes into the water

Nutrient delivered per degree of KH corrected (mg per litre)14 mg per litre

The nutrient supplied feeds the plantsyes

Sodium added per degree of KH corrected (mg per litre)0 mg per litre

Suitable for a closed circuit with little water renewalyes

Use in aquaponics

Corrects a potassium deficiencyyes

Corrects a calcium deficiencyno

Not recommended in aquaponics by the FAOno

Usable alone as the sole KH correctoryes

Sodium bicarbonate

Effect on KH

Dose to raise KH by one degree in 1 cubic metre (g)30 g

Solubility in water at 20 degrees (g per litre)96 g per litre

Dissolves completely at the working doseyes

Effect achieved in under an houryes

What goes into the water

Nutrient delivered per degree of KH corrected (mg per litre)0 mg per litre

The nutrient supplied feeds the plantsno

Sodium added per degree of KH corrected (mg per litre)8,2 mg per litre

Suitable for a closed circuit with little water renewalno

Use in aquaponics

Corrects a potassium deficiencyno

Corrects a calcium deficiencyno

Not recommended in aquaponics by the FAOyes

Usable alone as the sole KH correctorno

Calcium carbonate

Effect on KH

Dose to raise KH by one degree in 1 cubic metre (g)18 g

Solubility in water at 20 degrees (g per litre)0,013 g per litre

Dissolves completely at the working doseno

Effect achieved in under an hourno

What goes into the water

Nutrient delivered per degree of KH corrected (mg per litre)7,1 mg per litre

The nutrient supplied feeds the plantsyes

Sodium added per degree of KH corrected (mg per litre)0 mg per litre

Suitable for a closed circuit with little water renewalyes

Use in aquaponics

Corrects a potassium deficiencyno

Corrects a calcium deficiencyyes

Not recommended in aquaponics by the FAOno

Usable alone as the sole KH correctorno

The doses are calculated for one German KH degree, i.e. 17.85 mg/L of calcium carbonate equivalent. Calcium carbonate shows the lowest theoretical dose because it provides two charges per molecule, but it only dissolves to 13 mg/L in neutral water: at the effective dose, some remains on the bottom, acts over several days, and stops once the water is no longer acidic. It is a slow buffer, not a corrector. No pricing is included in this table: the shop sells in several currencies and the other two products are not in our catalogue, so a fixed figure would be incorrect for some visitors.

Estimate your
delivery time

Potassium bicarbonate is dispatched in standard parcels of 1 or 2 kg, with no special transport restrictions: it is not classified as a hazardous material. The delivery times shown are those quoted by carriers for the destination, calculated from the date of dispatch and excluding peak periods. The exact price depends on the total weight of your basket and the delivery method selected; it is displayed at checkout, in your currency.

Frequently asked questions

12 questions

6 key questions, 12 in the detailed view

How much potassium bicarbonate is needed to raise the KH by one degree?

36 gper m³ per degree of KH

3.6 gper 100 litres

200 L: approximately 7 g per degree.
500 L: approximately 18 g per degree.
1,000 L: approximately 36 g per degree.
3,000 L: approximately 108 g per degree.

The figure comes from the following calculation: one German degree of KH equals 17.85 mg/L of calcium carbonate equivalent, and the molar mass of potassium bicarbonate is 100.12 g/mol. A French field reference puts it closer to 39 g. The difference is small: start with the lower value and measure again 24 hours later.

A higher KH than necessary is not harmful, but it does make the water harder to bring back down if you later need a low pH for certain crops. For a significant correction, raise by one to two degrees per day — less for the sake of pH than to give the fish and bacteria time to adjust to the change in mineralisation.

What is the difference from sodium bicarbonate, which costs less?

Both raise KH effectively, and sodium bicarbonate requires slightly less to do so. The difference lies elsewhere: in what remains in the water.

Product	Dose per degree	What remains in the water	In a closed circuit
Sodium bicarbonate	30 g/m³	8.2 mg/L of sodium	neither taken up by plants nor removed by the biofilter: it accumulates indefinitely
Potassium bicarbonate	36 g/m³	14 mg/L of potassium	a useful nutrient for plants

Twenty-two one-degree corrections using sodium bicarbonate are enough to reach 184 mg/L, the threshold above which lettuce, cucumber, and pepper begin to suffer according to Wageningen research on soilless cultivation. At one correction per month, that is less than two years.

The FAO is unequivocal in its small-scale aquaponics manual: sodium bicarbonate should never be used in aquaponics, due to the increase in sodium, which is harmful to plants.

Is potassium bicarbonate harmful to fish?

At the doses used to correct KH, no. A study conducted on African catfish measured no effect on growth up to 600 mg/L of potassium in the water, and observed a decline only above 670 mg/L; the range it recommends to balance the needs of plants and fish is 200 to 400 mg/L. Correcting one degree of KH adds only 14 mg/L of potassium: it would take more than forty successive corrections, with no water changes and no uptake by the plants, to approach the lowest concentration at which any effect was observed.

These figures relate to a single species. The margin is wide, but it is not unlimited: increase gradually and measure as you go. The real safeguard lies elsewhere: the product cannot push the pH beyond approximately 8.3, so the classic risk associated with pH correctors — alkaline shock — does not apply here.

How do I know if my system needs it?

Three signals on the water side, four on the plant side.

Water side

a pH persistently below 6.5;
a KH below 3 or 4 degrees;
a pH that drops again a few days after each correction, a sign that the buffer reserve is exhausted.

Plant side

edges of older leaves turning yellow then brown;
flowers that abort;
small, poorly coloured or splitting fruit;
soft stems despite green foliage.

The plant-side signals alone are not enough to draw conclusions: several deficiencies look alike, and our guide to identifying deficiencies in aquaponics helps to tell them apart. A KH test settles the question in two minutes and costs less than a misdiagnosis.

Can the pH rise too high if I add too much?

How do you dissolve it and exactly where do you pour it?

Weigh the quantity on a kitchen scale, to the gram. A spoon is not a measure: the density of the powder varies depending on whether it is compacted or not.
Pour it into a bucket containing approximately one litre of lukewarm system water, and stir until fully dissolved. This happens quickly: the product dissolves at over 220 g per litre.
Pour the solution into the sump or in front of the pump outlet, where the turbulence is greatest.
Never pour directly onto the grow medium, onto the roots, or near the fish.
Leave the circulation running normally and wait 24 hours before measuring again.

Neither the pump, the biofilter, nor the aeration needs to be switched off. The confusion stems from sodium percarbonate, a completely different product, which releases active oxygen and requires the circulation and filter to be stopped for the duration of the treatment.

How often does it need to be added?

Do not schedule additions on fixed dates. The rate of acidification depends on the fish load, the amount of food given, and the water volume: there is no universal timetable — it is the KH that dictates the rhythm.

Test the KH once a week at start-up, then once a fortnight once you know your pattern. As soon as it drops below 4 degrees, correct it to bring it back into the 4 to 8 range, and note the date and dose: after two or three corrections, you will know your actual interval.

In practice, most domestic systems require a top-up every two to six weeks. A practical benchmark, drawn from a single source and therefore to be treated as an approximate guide, links consumption to feeding: 150 to 190 g of bicarbonate per kilogram of food fed to the fish.

What is the difference from potassium hydroxide, which is often cited in aquaponics?

Both raise potassium levels and push the pH up. The difference lies in how aggressively they do it.

Potassium hydroxide is a strong, corrosive base whose solutions reach around pH 13. Added too quickly, it creates a localised zone of extremely high pH before the water mixes, which stresses fish and can damage the biofilter colonies. It raises pH without rebuilding the carbonate buffer, so the pH drops back just as fast.

Potassium bicarbonate tops out at around pH 8.3: it simply cannot cause that kind of accident, and it also adds carbonates, giving you more KH. The FAO cites both, noting that carbonates are the safer option because they increase hardness at the same time as pH.

Does potassium bicarbonate replace a potassium fertiliser?

No, not to correct an established deficiency: each degree of KH corrected adds only 14 mg/L of potassium, whereas the nutritional target cited for plants is around 40 to 70 mg/L, and at one correction per month the cumulative input is real but slow. It is a free bonus, not a fertiliser: our article on which fertiliser to use in aquaponics compares the options, and a potassium test will tell you where you stand before you decide.

Should you stop the pump, the biofilter or the aeration while adding it?

Can it be used as a fungicide on leaves?

Potassium hydrogen carbonate is indeed an approved fungicidal active substance in organic farming, particularly against powdery mildew and scab, and commercial preparations based on it do exist. Foliar dilutions cited by distributors are typically around 5 to 10 g per litre.

We do not sell this product as a plant protection product and do not recommend this use from this page. A registered foliar treatment involves regulations, dosages, and precautions that go beyond the scope of a KH adjuster. If this is something you wish to pursue, please consult a preparation that is authorised for this specific use.

How long does a bag keep, and what should you do if it hardens?

When kept dry, shelf life has no practical limit. The compound does not degrade at room temperature: it only breaks down above 292 degrees. In an airtight container, kept between 15 and 25 degrees, it remains unchanged.

A hardened packet is not out of date. The only enemy is moisture: the powder is hygroscopic and, if left open to the air, it absorbs ambient moisture and sets into a lump. Its composition is unchanged and it dissolves just as well; simply crumble it and weigh as normal. To avoid the problem, transfer it to a sealed jar as soon as you open it.

How much to add to your system

Enter the total water volume of your system, pond and growing beds included. The calculation gives the quantity of powder to weigh out.

System water volume

50 L10000 L

to raise the KH by one degree

To raise the KH by three degrees

0 g

Calculation basis: one German KH degree equals 17.85 mg/L of calcium carbonate equivalent, or 35.7 mg of potassium bicarbonate per litre, rounded to 36 g per cubic metre. A practical field reference gives 39 g: if your 24-hour reading shows a gain of less than one degree, increase the next dose by around 10%. Never raise the KH by more than one to two degrees per day, and leave 48 hours between doses.

Let us talk about your project

Une question sur ce produit ou votre installation ? Notre équipe vous répond et vous conseille.

Email us Contact form

Paiement plusieurs fois sans frais

Proposé selon le montant du panier, au moment du paiement.

Livraison sous 5 à 15 jours ouvrés

Selon les produits et sites d'expédition. Estimation par destination dans l'estimateur de cette page.

SAV 7/7 par mail ou chat

Notre équipe répond à toutes vos questions.

Faire un achat engagé

Devenez acteurs du changement.

Potassium Bicarbonate

The summary

Raises pH, restores KH and adds potassium, without introducing sodium.

How much to use, and what effect to expect

Potassium rather than sodium: what the calculation shows

When to add it, and how often

Technical specifications

Potassium bicarbonate, sodium bicarbonate or calcium carbonate

Estimate your
delivery time

Frequently asked questions

How much to add to your system

Vous aimerez aussi

Related articles

Regulating pH in an aquaponics system

Plant deficiencies in aquaponics

The nitrogen cycle in aquaponics

What fertilizer should I use in aquaponics ?

Recognizing deficiencies in aquaponics

Common Mistakes in Aquaponics

Let us talk about your project

Potassium Bicarbonate

The summary

Raises pH, restores KH and adds potassium, without introducing sodium.

How much to use, and what effect to expect

Potassium rather than sodium: what the calculation shows

When to add it, and how often

Technical specifications

Potassium bicarbonate, sodium bicarbonate or calcium carbonate

Estimate yourdelivery time

Frequently asked questions

How much to add to your system

Vous aimerez aussi

Related articles

Regulating pH in an aquaponics system

Plant deficiencies in aquaponics

The nitrogen cycle in aquaponics

What fertilizer should I use in aquaponics ?

Recognizing deficiencies in aquaponics

Common Mistakes in Aquaponics

Let us talk about your project

Estimate your
delivery time