A small heap of potassium bicarbonate, a fine white powder, set against a white background

Potassium bicarbonate powder for aquaponics

$31.00

Weight	Price	Price per kg	vs 1 kg
1 kg	$31.00	$31.00	—
2 kg	$58.00	$29.00	−6 %

Potassium bicarbonate offsets the acidification that nitrification produces continuously in an aquaponic system. It raises the pH, rebuilds the KH and supplies the plants with potassium, without adding any sodium.

A bicarbonate solution levels off at around pH 8.2: even if you overdose, it does not cause the alkaline shock that a potash would.

Potassium bicarbonate

Weight : 1 kg

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The summary

How much to add: about 36 g per cubic metre of water to raise KH by one degree. The calculator works it out for your volume.
What it changes in the water: one degree of KH regained, and 14 mg/L of potassium supplied to the plants along the way.
Potassium, sodium or calcium: sodium bicarbonate adds 8.2 mg/L of sodium per degree corrected, and this sodium accumulates in a closed circuit.
Safe for fish: no measured effect on growth up to 600 mg/L of potassium, far above the doses actually needed.
What is in the sachet: potassium bicarbonate powder, 1 kg or 2 kg, and nothing else.
Shipping: standard parcel of 1 to 2 kg, allow 3 to 5 working days in mainland France.

KH and pH corrector that supplies potassium to plants, without adding sodium

Potassium bicarbonate powder for aquaponics is used to offset the continual acidification caused by nitrification, by raising KH and pH. About 36 g per cubic metre is needed to raise KH by 1 degree, with 14 mg/L of potassium supplied to the plants, without the sodium that sodium bicarbonate would leave behind.

In an aquaponic system, the pH falls steadily and predictably. The bacteria in the biofilter oxidise the fish's ammonia and release H+ ions in the process, which uses up your alkaline reserve day after day, as described in the article on the nitrogen cycle in aquaponics. Potassium bicarbonate rebuilds that reserve and supplies the nutrient that plants most often lack.

⚖️ The dose and the expected effect

You need 36 grams per cubic metre to raise KH by one degree. Start with that figure, measure the next day, then adjust. The dosage calculator works it out for your volume, and a KH test tells you where you stand before you pour anything in. For an 800-litre system whose KH has fallen to 3, bringing KH up to 6 takes about 86 g, added in two doses of 43 g spaced 48 hours apart. Aim for a KH of 6 to 12 degrees and a pH of 6.4 to 7.5, and never raise KH by more than two degrees a day.

🥗 Potassium, a bonus nutrient

Potassium bicarbonate contains 39% potassium by mass, so every degree of KH you correct supplies 14 mg of potassium per litre. This nutrient is often deficient in aquaponics, because fish feed contains little of it relative to the needs of fruiting vegetables. As it is mobile within the plant, its deficiency shows first on the edges of the older leaves. Your plants take it up as they go, so it does not build up in the water.

This is the fundamental difference from sodium bicarbonate. Each degree corrected with it adds 8.2 mg of sodium per litre, which the plants do not consume and the biofilter does not remove. In a closed loop, this sodium accumulates from one addition to the next until it reaches the threshold at which the yield of lettuce and cucumber falls, and this is why the FAO aquaponics manual rules out sodium bicarbonate.

The pH 8.2 ceiling

A bicarbonate solution settles at around pH 8.2: however much you add, the product cannot push the water any higher, whereas a potash solution reaches pH 13. This ceiling rules out the caustic shock of a strong base, but it doesn't excuse you from measuring, since 8.2 already exceeds the 6.4 to 7.5 range aimed for in aquaponics. The KH test therefore sizes the dose: it tells you how many degrees are missing before you add it, and then what you have gained the next day.

Dissolve the powder and correct in stages

The powder is not classified as hazardous, but its dust can irritate the eyes: pour it without stirring it up and rinse with clean water in case of contact. Never pour the dry powder into the pond, as it becomes concentrated locally before it dilutes; pre-dissolve it in a bucket of lukewarm water. Do not try to put everything right in one go either: raise the KH by one to two degrees a day at most, leaving 48 hours between two additions, so that the fish and the bacteria can keep up. Finally, reseal the bag after each use, as the powder absorbs moisture from the air and cakes.

⚗️ Why KH drops

Nitrification converts the ammonia nitrogen excreted by the fish into nitrite and then nitrate, and this oxidation releases acidity that bicarbonate ions neutralise as they are used up. Each gram of nitrified nitrogen therefore consumes around 7.1 g of alkalinity, expressed as calcium carbonate, which corresponds to almost 14 g of potassium bicarbonate. The rate of decline therefore follows the amount of feed you give: it speeds up when the water warms and the fish eat more, and slows down in winter. This is why a weekly test tells you more than a fixed calendar.

🔄 Potassium and calcium in rotation

The FAO aquaponics manual advises alternating potassium-based and calcium-based correctors, such as calcium carbonate or calcium hydroxide, since each supplies a different nutrient while rebuilding the same buffer. Potassium bicarbonate meets the potassium needs of fruiting vegetables. If your tap water is soft and the hearts of your young leaves are turning black, a sign of calcium deficiency, using a calcium corrector every second time balances the supply. Note down the date, the product and the dose each time: within a few months you will know which rhythm suits your system.

Technical specifications

Dosage and effect on the water

Dose per degree of KH: 36 g per cubic metrePre-dissolve the powder in a bucket of lukewarm water before pouring it in.
Potassium supplied: 14 mg/L per degree correctedA nutrient that fish feed supplies in small amounts and that plants use up as they go.
Maximum achievable pH: Around 8.2, whatever the doseA property of the bicarbonate ion. Overdosing is best avoided: 8.2 exceeds the target range in aquaponics.
KH to aim for in aquaponics: 6 to 12 degreesBelow 6, the buffer reserve thins out and the pH becomes less stable from one day to the next.
pH to aim for in aquaponics: 6.4 to 7.5A compromise between the nitrifying bacteria, which prefer a more alkaline pH, and nutrient availability.
Maximum daily increase: 1 to 2 degrees of KHAllow 48 hours between doses: beyond that, fish and bacterial colonies do not have time to adapt.

To budget for separately

Gram-accurate scales: A set of kitchen scales36 g per cubic metre and per degree of KH cannot be measured out by the spoonful.
KH test: Carbonate hardness testIt tells you how many degrees are missing, before and 24 hours after the addition.
pH test: pH drop testpH is the signal that triggers the addition, KH is the measurement that sizes it.
Airtight container: Jar or bucket with a sealA bag left open cakes together and can no longer be weighed.

2 further specifications are available in the detailed view.

In the box

1 sachet of potassium bicarbonate powder, in the pack size selected
White crystalline powder, odourless, with no colouring or additives

Dose of 36 g per cubic metre: stoichiometric calculation. Physico-chemical properties taken from chemical databases. Fish thresholds taken from a study on African catfish, not directly transferable to all species. Recorded on 10/09/2026.

Potassium bicarbonate or calcium carbonate

Both raise the KH. What sets them apart is what they leave in the water once the buffer has been rebuilt, and how quickly they take effect. Sodium bicarbonate is not included: its sodium builds up in a closed system, and the FAO advises against it in aquaponics.

Both raise KH, but not with the same ion What sets them apart is what they leave in the water once the buffer has been restored, potassium or calcium, and how quickly they work.

	Dose for one degree of KH 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 supplied per degree of KH corrected (mg per litre)	The nutrient supplied feeds the plants	Corrects a potassium deficiency	Corrects a calcium deficiency	Can be used as the sole KH corrector
Recommended Potassium bicarbonateYour choice	36 g	224 g per litre	Yes	Yes	14 mg per litre	Yes	Yes	No	Yes
Calcium carbonateYour choice	18 g	0,013 g per litre	No	No	7,1 mg per litre	Yes	No	Yes	No

Potassium bicarbonateRecommended

Effect on KH

Dose for one degree of KH 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 supplied per degree of KH corrected (mg per litre)14 mg per litre

The nutrient supplied feeds the plantsYes

Use in aquaponics

Corrects a potassium deficiencyYes

Corrects a calcium deficiencyNo

Can be used as the sole KH correctorYes

Calcium carbonate

Effect on KH

Dose for one degree of KH 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 supplied per degree of KH corrected (mg per litre)7,1 mg per litre

The nutrient supplied feeds the plantsYes

Use in aquaponics

Corrects a potassium deficiencyNo

Corrects a calcium deficiencyYes

Can be used as the sole KH correctorNo

Doses calculated by stoichiometry for one German degree of KH, i.e. 17.85 mg/L of calcium carbonate equivalent. Solubilities taken from chemical databases, consulted on 10/09/2026.

Estimate your
delivery time

Potassium bicarbonate ships as a standard parcel of 1 or 2 kg, with no special transport requirements: it is not classed as a dangerous substance. The delivery times shown are those quoted by the carriers for the destination, counted from dispatch and excluding peak periods. The exact rate depends on the total weight of the basket and the delivery method chosen; it is displayed at checkout, in your currency.

Frequently asked questions

8 questions

6 key questions, 8 in the detailed view

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

36 gper m³ and per degree of KH

3.6 gper 100 litres

For 200 L, allow about 7 g per degree.
For 500 L, allow about 18 g per degree.
For 1,000 L, allow about 36 g per degree.
For 3,000 L, allow about 108 g per degree.

Start with this amount, test 24 hours later, then adjust according to your readings.

A higher KH than necessary is not dangerous, but it makes the water harder to bring down afterwards if you are aiming for a low pH for certain crops. For a large correction, raise the KH by one to two degrees per day at most, less for the pH than to give the fish and bacteria time to adapt to the change in mineralisation.

What is the difference compared with sodium bicarbonate, which costs less?

Both raise KH effectively, and sodium bicarbonate actually requires a little less. The difference lies in what is left in the water.

Product	Dose per degree	What stays in the water	In a closed circuit
Sodium bicarbonate	30 g/m³	8.2 mg/L of sodium	neither consumed by the plants nor removed by the biofilter: it builds up from one addition to the next
Potassium bicarbonate	36 g/m³	14 mg/L of potassium	a nutrient useful to plants

After 23 one-degree corrections with sodium bicarbonate, the sodium exceeds 184 mg/L, the threshold above which the yield of lettuce, cucumber and pepper declines in soilless cultivation. At one correction a month, that takes less than two years.

The FAO advises against sodium bicarbonate in aquaponics, precisely because of this sodium accumulation, which is harmful to plants.

Is potassium bicarbonate dangerous for fish?

At the doses used to correct KH, no. In African catfish, no effect on growth appears up to 600 mg/L of potassium in the water, and the decline only begins beyond 670 mg/L; the recommended range for reconciling plants and fish is 200 to 400 mg/L. Yet correcting one degree of KH adds only 14 mg/L of potassium: you would need more than 40 successive corrections, with no water change and no uptake by the plants, to approach the first concentration at which an effect was observed.

The margin is wide, but it is not infinite: raise the KH gradually and measure. The product cannot push the pH beyond about 8.2, which rules out the caustic shock of a potash-based corrector, but not the excess: at 8.2, the water leaves the 6.4 to 7.5 range targeted in aquaponics.

Can the pH become too high if you overdose?

Not beyond pH 8.2 or so: whatever the dose, a bicarbonate solution does not exceed this value, which rules out the caustic shock of a strong base such as potash.

In aquaponics, however, 8.2 is still too high. Above 7, iron becomes less available to the plants, and a growing share of the ammoniacal nitrogen shifts to its free form, which is toxic to fish. An overdose therefore costs you in deficiencies and stress, even without burn: aim for 6.4 to 7.5 and correct in stages.

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

Weigh out the quantity on a kitchen scale, to the gram. A spoon is not a measurement: the density of the powder varies depending on whether it is packed down or not.
Pour it into a bucket containing about 1 litre of water from the system, and stir until fully dissolved. This is quick: the product dissolves at more than 220 g per litre.
Pour the solution into the sump or in front of the pump outlet, where the mixing is strongest.
Never pour it directly onto the grow medium, onto the roots, or near the fish.
Let the circulation run normally and wait 24 hours before measuring again.

There is no need to switch off the pump, the biofilter or the aeration during the addition.

How often should it be added?

Do not schedule additions on fixed dates. The speed of acidification depends on the fish load, the amount of feed given and the volume of water: there is no universal calendar, and it is the KH that decides.

Test the KH once a week at start-up, then once a fortnight when you know your own rhythm. As soon as it drops below 6 degrees, correct it to bring it back into the range of 6 to 12, and note the date and the dose: after two or three corrections, you will know your real interval.

In practice, most home systems need an addition every 2 to 6 weeks. A rule of thumb from the field links consumption to feeding: 150 to 190 g of bicarbonate per kilo of feed given to the fish.

My pH stays low even though the KH has been corrected, why?

At the same KH, the pH also depends on the dissolved CO2: fish and bacteria produce it continuously, and poorly agitated water holds on to it, which lowers the pH without affecting the KH.

Measure the pH in the morning and at the end of the day; the difference tells you how much CO2 has built up overnight.
Increase aeration or surface agitation, which lets the CO2 escape.
Do not add bicarbonate as long as the KH stays within the range of 6 to 12 degrees.

Can it be used in an aquarium or an ornamental pond?

How much to pour into your system

Enter the total volume of water in your system, including the pond and grow beds. The calculation gives the amount 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

Basis of calculation: one German degree of KH equals 17.85 mg/L of calcium carbonate equivalent, or 35.7 mg of potassium bicarbonate per litre, rounded up to 36 g per cubic metre. A field reference gives 39 g: if your 24-hour reading shows a gain of less than one degree, increase by about 10% at the next addition. Never raise the KH by more than 1 to 2 degrees per day, and leave 48 hours between additions.

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Potassium bicarbonate powder for aquaponics

The summary