Les correcteurs pH- et pH+ de Terra Aquatica côte à côte

Disponibilité des éléments nutritifs selon le niveau de pH

pH correction duo: pH- and pH+

Name: pH correction duo: pH- and pH+
Brand: Terra Aquatica
SKU: TA-DUOPH-500
Price: 18.9 EUR
Availability: InStock

18,90 €

A pair of liquid pH correctors: the pH-, a blend of three buffered acids, and the pH+, based on potassium carbonate, to keep a nutrient solution between 5.5 and 6.8 in both directions, whether using hard tap water or reverse osmosis water. Available in 500 ml or 1 L each, corrosive concentrates H314.

Format : 2 x 500 ml

2 x 500 ml

2 x 1 L

7/7 customer service by e-mail

Payment in instalments, free of charge

The summary

What it is: both Terra Aquatica pH correctors together — one bottle of pH- and one bottle of pH+ — in the same size format.
Why both: hard water pushes pH up, RO water pulls it down. Many setups encounter both situations over the course of a year.
What they add: the pH- leaves a little phosphorus; the pH+ contributes potassium and silica. Neither is simply a DIY-grade acid.
How much to use: there is no fixed dose — it depends on the buffering capacity of your water. The small-additions method is covered in the FAQs.
Caution: both concentrates are corrosive, classified H314. Wear gloves and eye protection, and never pour one into the other.
Sizes and delivery: 2 x 500 ml or 2 x 1 L, shipped together in a single parcel from France.

Both correctors in the range, to adjust pH in either direction

This duo brings together the two pH correctors from the Terra Aquatica range: pH-, a yellowish bottle at pH 1 that lowers the value of a nutrient solution, and pH+, a pale blue bottle at pH 12 that raises it. These are professional correctors designed for hydroponics, coco fibre, and soil, available here in 500 ml or 1 L each. They work with any fertiliser, not just those from the same brand.

pH does not feed the plant: it determines what the plant can actually absorb. Between 5.5 and 6.5, all nutrients remain available. Above 6.8, iron and manganese lock up and young leaves start to pale; below 5.0, calcium and magnesium are poorly taken up and roots suffer. This is the most common cause of a crop that stagnates even when the fertiliser dosing is correct.

Why you need two, not just one

pH-, for tap water

Hard water is rich in bicarbonates: the pH rises back on its own a few hours after each correction. This is the bottle you will use the most.

pH+, for RO Water

Water with no buffering capacity drops at the slightest drop of acid, and fertilisers themselves are acidic. It will not recover on its own.

Both, for most people

As soon as mains water is replaced with rainwater, or when the season changes, the drift reverses direction during the year.

These are not simple off-the-shelf acids and bases. The pH- is a blend of three acids combined with organic buffers: this buffering capacity means that an adjusted value holds for several days rather than a few hours, whereas vinegar or citric acid break down within one or two days. The pH+ is based on potassium carbonate and additionally provides a source of silica, which thickens cell walls and stiffens stems.

Which bottle you will use the most

Your starting water	The bottle doing the work	How often
Hard water from the mains	pH-, almost exclusively	At every reservoir top-up, then a small adjustment every two to three days until the bicarbonates have been used up. The pH+ only comes out of the cupboard if you overcorrect.
Mains water blended with rainwater	pH- for part of the year, pH+ for the rest	The direction of drift shifts with the blend ratio, which changes with rainfall. Both bottles get used across the year, and neither runs out quickly.
RO water or pure rainwater	pH+, measured to a fraction of a millilitre	At every top-up, then as soon as the solution dips again, often within two or three days. The pH- is almost never needed: the fertilisers are already acidic and handle it on their own.

Frequencies observed on a reservoir refreshed every two weeks. They depend on your water's buffering capacity, not on any general rule.

The conclusion is less of a sales pitch than a straight answer, but more useful for it: the duo only makes sense if your water changes throughout the year, or if you want to be able to correct an overcorrection. If you grow year-round on mains water in a hard water area, pH- alone will do the job, and you'll buy that bottle two or three times before you even start on the other. If you grow exclusively on RO water, it's pH+ alone that you'll need.

The price points in the same direction and deserves to be stated plainly. At prices as of 25 August 2026, the duo in 500 ml costs 18.90 euros, whereas the two bottles bought separately cost 19.80 euros: the saving is 0.90 euros, and that's not a reason to buy the duo. In 1 L, 28.90 euros versus 31.80 euros bought separately, a saving of 2.90 euros. What you're actually buying here is the certainty of never being stuck on the day your pH drifts the wrong way, when your solution is already mixed and waiting for a delivery would cost you a week's growth. To find out which way your water is likely to drift before you have to decide, our article on pH regulation explains what buffering capacity is and how to identify it in your own setup.

Two corrosives, and above all, never mix one into the other

Both bottles carry the same warning: H314, causes severe skin burns and eye damage. A strong base burns just as badly as a strong acid. Gloves and eye protection for both, no decanting into food containers, and never pour pH+ into pH-: the reaction is vigorous and both are wasted in the process. Each one is poured into water separately.

The method, the same for both

Adjust last, after adding the fertilisers, because each one shifts the value. Add in small amounts, stir for twenty minutes, then measure before repeating: the buffer takes time to act, and measuring too soon leads to overcorrection. With hard water, the first adjustments consume the bicarbonates; once that's done, the value holds for several days and subsequent additions become minimal.

The mistakes that send you back and forth

Four ways to waste both bottles for nothing

Correcting before adding the fertilisers. The three TriPart parts are acidic: they bring the value down on their own, sometimes by several tenths of a point. Correcting plain water means raising it with pH+ only for the fertilisers to pull it back down ten minutes later, then chasing it again with pH-. Add the fertilisers, mix thoroughly, and only then make your correction.

Measuring too soon after adding the corrector. A buffered corrector does not act instantly: the value keeps shifting for a good quarter of an hour. Measuring within the first minute gives a reading that is too high or too low, prompting you to add more, and the full correction overshoots the target. Stir, wait twenty minutes, measure, and only then decide.

Correcting a pH that would have risen on its own. In hard water, the value rises by itself over the following hours as long as the bicarbonates have not been neutralised. Chasing every tenth of a point in the first few days means fighting against the water. Holding a range of 5.5 to 6.5 is a perfectly adequate target, it is not a single fixed value to maintain.

Overcorrecting, then compensating with the other bottle. This is the costliest mistake, and not only in terms of product. Every back-and-forth leaves behind whatever the corrector introduces, phosphates on one side, potassium on the other: conductivity rises without anything extra reaching the plant, and the elemental imbalance takes hold. When you have gone too far, diluting with a little fresh water is better than correcting in the opposite direction. None of this is measurable without the right instruments, see the water analysis collection and our article on common mistakes.

Without a measuring instrument, these two bottles are completely useless

To the naked eye, there is nothing to distinguish a solution at 6.0 from one at 7.2, yet the difference in nutrient availability between the two is considerable. A calibrated pH meter or a colourimetric drop test kit is the essential companion to this duo: see the water analysis collection.

This duo naturally complements the TriPart system, whose feeding chart sets a pH target for each stage: 5.5 to 6.5 up to pre-flowering, then 6.4 to 6.8 afterwards. If you are setting up a complete installation, the full TriPart pack brings together all three fertilisers and the pH- in one litre. And to understand why water without a buffer is harder to stabilise than hard water, contrary to what you might expect, our article on pH regulation explains it in detail.

Technical specifications

What the duo contains

pH- corrector: 1 bottleBlend of three acids with organic buffers. Yellowish liquid, pH 1. Orthophosphoric acid at 5 to 10 per cent.
pH Up corrector: 1 bottlePotassium carbonate 10 to 20 per cent, silica source. Pale blue liquid, pH 12.
Available sizes: 500 ml or 1 LBoth bottles always come in the same size within the duo.
Growing methods: Hydro, coco and soilCompatible with any fertiliser, including those from other brands.
Target pH range: 5.5 to 6.5The range in which the plant takes up all nutrients. During flowering, the target rises to 6.4–6.8.
Dosage: Varies with waterNo dose per litre exists for a pH corrector: it all depends on the buffering capacity of the water being treated.

Safety and storage

Classification of both: Danger, H314Causes severe skin burns and serious eye damage. Corrosive category 1A for both.
Required equipment: Gloves and gogglesSafety precautions P264 and P280, identical on both bottles.
Strictly prohibited: Never mix them togetherA strong base and a strong acid react vigorously and neutralise each other. Each must be added to water — never to the other.
If swallowed: Do not induce vomitingRinse your mouth and contact a poison control centre.
Storage: Separate, upright, frost-freeDo not store them side by side on the same sloping shelf. pH+ crystallises in the cold.
Manufacture: Fleurance, FranceTerra Aquatica, formerly General Hydroponics Europe.

4 further specifications are available in the detailed view.

In the box

1 bottle of pH- adjuster in the chosen size, 500 ml or 1 L.
1 bottle of pH+ corrector in the same size.
No pH meter, no colorimetric test kit and no calibration solution: see the water testing collection.
No gloves or safety goggles are included. Please provide your own: both concentrates are classified H314.
No pipette or dosing syringe included.

The H314 classifications, declared compositions, pH values, and densities of both concentrates are taken from their respective French safety data sheets — dated 22 November 2023 for pH- and 8 January 2024 for pH+. The descriptions of the blend of three acids and the silica source, along with the 5.5 to 6.5 range, are taken from the manufacturer's 2025 French catalogue, page 20. This duo is assembled by us from the two references sold separately: it is not a manufacturer's packaging.

The two correctors in the duo, side by side

The duo contains both. This table shows which one you will use most depending on your water, and what each one contributes beyond pH correction.

	Effect on the solution	Water affected	The one you'll use most with tap water	The one you'll use most with RO water	Active base	Concentrate pH	Liquid colour	Supplies phosphorus	Supplies potassium	Silica source	Classified corrosive H314	Gloves and goggles required	Never mix with the other
pH Down correctorYour choice	Lowers pH	Hard tap water	yes	no	Three buffered acids	1	Yellowish	yes	no	no	yes	yes	yes
pH Up correctorYour choice	Raises pH	RO or rainwater	no	yes	Potassium carbonate	12	Pale blue	no	yes	yes	yes	yes	yes

pH Down corrector

What each one does

Effect on the solutionLowers pH

Water affectedHard tap water

The one you'll use most with tap wateryes

The one you'll use most with RO waterno

Active baseThree buffered acids

Concentrate pH1

Liquid colourYellowish

What it brings extra

Supplies phosphorusyes

Supplies potassiumno

Silica sourceno

Safety

Classified corrosive H314yes

Gloves and goggles requiredyes

Never mix with the otheryes

pH Up corrector

What each one does

Effect on the solutionRaises pH

Water affectedRO or rainwater

The one you'll use most with tap waterno

The one you'll use most with RO wateryes

Active basePotassium carbonate

Concentrate pH12

Liquid colourPale blue

What it brings extra

Supplies phosphorusno

Supplies potassiumyes

Silica sourceyes

Safety

Classified corrosive H314yes

Gloves and goggles requiredyes

Never mix with the otheryes

Both bottles in the duo are always in the same size, 500 ml or 1 L depending on your choice. The compositions, concentrate pH values and classifications are taken from the manufacturer's French safety data sheets. The description as a blend of three acids and as a silica source is taken from the French 2025 catalogue, page 20. Prices are not shown in this table: they are correct elsewhere on the page, in your currency.

Documents & manuals

Safety data sheet for pH-, in French

Version dated 22 November 2023. H314 classification, composition, protective equipment and procedure in case of contact.

PDF · 4

Download

Safety data sheet pH-, in English

Version 8 dated 22 November 2023. Same content as the French sheet: H314 classification, acid composition, protective equipment and procedure to follow in case of contact. Document in English.

PDF · 4

Download

Safety data sheet for pH+, in French

Version dated 8 January 2024. Same H314 classification, potassium carbonate content, and storage precautions.

PDF · 4

Download

Safety data sheet pH+, in English

Version 8 dated 8 January 2024. Same H314 classification, potassium carbonate content and storage precautions as the French version. Document in English.

PDF · 4

Download

TriPart application chart, with pH targets by growth stage, multilingual document

The pH and conductivity ranges to aim for at each stage of growth, which these two correctors help you maintain. A multilingual document with French and English side by side: no separate English-only version exists.

PDF · 4

Download

Estimate your
delivery time

Both bottles are shipped in the same parcel, avoiding two separate delivery charges. Approximately 1.1 kg for the 500 ml size, 2.2 kg for the 1 L size. Corrosive products under CLP classification, shipped in their original packaging. The exact shipping costs are displayed at checkout once your address has been entered.

Frequently asked questions

14 questions

6 key questions, 14 in the detailed view

Do I need both, or just the pH-?

That depends on the water you add to the reservoir.

Your water	What happens to the pH	What you need
Hard tap water	It rises on its own	Mainly pH-
RO or rainwater	It drops and won't come back up	Mainly pH+
A mix of both, or moderately hard water	It drifts in both directions	The duo

The third case is the most common as soon as you collect rainwater for part of the year.

How much do you save compared to buying the two bottles separately?

Can you mix pH+ and pH-?

What pH should I aim for in my reservoir?

Should you correct before or after adding the fertiliser?

Which size to choose, 500 ml or 1 L?

2 x 500 ml: for one or two tanks, with low-calcium water. This is the format that suits the majority of home setups.
2 x 1 L: for very hard water, multiple tanks, or ongoing production, where each preparation uses noticeably more corrector.

Consumption depends far more on your water than on the volume you are growing: your first correction will tell you which format to go for next time.

How much product is needed for 10 litres of water?

There is no answer in millilitres, and you should be wary of any you find elsewhere. The quantity depends entirely on the buffering capacity of your water: rainwater will drop with just a few drops, while hard tap water may need ten times as much to achieve the same result.

Note down the quantity you needed the first time: it will hold true for every subsequent batch as long as you keep using the same water.

Do these pH adjusters work with a fertiliser from another brand?

My pH rises on its own the next day — is that normal?

Is it safe to keep at home?

Both bottles are classified H314, corrosive. Store them upright, closed, out of reach of children, in their original packaging, which carries the required labelling. Never decant into a food-grade bottle, and do not store them side by side on a slanted shelf.

Once diluted in a reservoir at working concentrations, they pose no risk: it is the concentrate that is hazardous, not the corrected solution.

What is the difference between this and vinegar or bicarbonate?

All three pairs shift the pH. What separates them is how long the effect holds.

Adjuster	Holding power	Side effect
Duo Terra Aquatica	Several days	Adds phosphorus, potassium and silica
Vinegar	A few hours	Feeds bacteria, clouds the water
Bicarbonate	Variable	Raises the sodium load of the solution

In a reservoir refreshed every day, the difference matters little. In a solution that runs for two weeks, it changes everything.

Can they be used in aquaponics?

Not like hydroponics. A stocked pond cannot tolerate a sudden shift in pH, and nitrifying bacteria even less so: a correction made too quickly can shut down biological filtration and cause ammonia to rise.

If a correction is necessary, it should be made in very small increments over several days, with daily monitoring. Our article on pH regulation in aquaponics covers precautions that are quite different from those applicable to a hydroponic reservoir.

Do you need a pH meter, or is a drop test sufficient?

Is this the manufacturer's original packaging?

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pH correction duo: pH- and pH+

The summary