Terra Aquatica pH- and pH+ adjusters side by side

Nutrient availability chart by pH, between the too-acidic zone and the too-alkaline zone

pH correction duo: pH- and pH+

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

16,90 €

~~18,80 €~~ 16,90 €

5,63 € × 3 with no fees Klarna.

This duo brings together the two liquid pH adjusters: pH-, based on nitric, phosphoric and citric acids, and pH+, based on potassium carbonate. They keep a nutrient solution between 5.5 and 6.8, whether you need to lower or raise the pH, with both hard tap water and RO water.

Each bottle is available in 500 ml or 1 L. These concentrates are corrosive, classified H314.

Ref. TA-DUOPH-500·pH adjuster

Format : 2 x 500 ml

2 x 500 ml

2 x 1 L

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The summary

What it is: both Terra Aquatica pH correctors in one purchase — a bottle of pH- and a bottle of pH+, in the same format.
Why both: hard water pushes the pH back up after every correction, while RO water lets it drop. Many systems encounter both situations over the course of a year.
What they add: the pH- contributes a little nitrogen and phosphorus, while the pH+ supplies potassium and silica.
How much to use: 4 ml of pH- per 50 L, or 1 ml of pH+ per 10 L to start, then adjust in small increments.
Important: both concentrates are corrosive, classified H314. Wear gloves and eye protection, and never pour one into the other.
Formats and shipping: 2 x 500 ml or 2 x 1 L, dispatched together in a single parcel from France.

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

This duo brings together both liquid pH correctors from the range, in the same 500 ml or 1 L format. The pH-, a yellowish liquid at pH 1, lowers the value of a nutrient solution; the pH+, a blue liquid at pH 12, raises it. They act on the water rather than on the fertiliser, so you use them alongside your usual fertilisers, whether in hydroponics, coco fibre, or soil.

🎯 Two limits to maintain

The pH value determines nutrient availability. During rooting and growth, the target range is 5.5 to 6.5; in pre-flowering and flowering, the TriPart system's application chart raises this to 6.4 to 6.8. Above this range, iron and manganese become less available and young leaves pale, whereas below 5.8 calcium is absorbed less effectively. A system can drift out of range in either direction, which is exactly why the duo keeps both correction options to hand.

🧭 The two directions of correction

The two bottles have neither the same chemistry nor the same contributions. The pH- combines nitric, phosphoric and citric acids: the first two lower the value as soon as they are added, the citric acid maintains it over time, and each correction leaves a small amount of nitrogen and phosphorus in the solution. The pH+ is based on potassium carbonate guaranteed at 13%, with 0.5% silica, which strengthens stem structure. Their effect is immediate, allowing you to take a reading as soon as the solution has been mixed.

pH-, for tap water

Hard water contains bicarbonates that raise the value after every correction: this is the most frequently used bottle.

pH+, for RO water

Water with no buffering capacity will see its pH drop as soon as fertiliser is added, since fertilisers are acidic by nature.

Both within the year

If you mix tap water with rainwater, the direction of correction changes with the proportions used.

Knowing which of the two bottles you will use most

The carbonate hardness test measures the bicarbonates in your water, that is, the buffering capacity that determines which bottle to choose. Water with several degrees of KH pushes the pH back up after each correction and mostly calls for pH-. Water close to 0 °dKH, such as RO or rainwater, requires pH+ instead as soon as the fertilisers are added. A measurement of your starting water therefore tells you which product to keep on hand going forward.

Never pour one corrector into the other

Never pour pH+ into pH-, or vice versa: a concentrated acid and a concentrated base react vigorously and neutralise each other. Each is poured directly into the reservoir water using its own separate syringe. Both concentrates carry the H314 designation, severe skin burns and serious eye damage: wear gloves and eye protection for both, and never transfer them into a food-grade container.

🥄 The first doses

Prepare the solution with your fertilisers first, then take a reading. If the pH exceeds the target range, start with 4 ml of pH- per 50 litres; if it falls below 5.5, start with 1 ml of pH+ per 10 litres. Mix, measure again, then add in small increments until you reach the desired value. pH- is dosed by the millilitre in hard water, whereas pH+ is often dosed to the tenth of a millilitre in osmosis water, which responds to very small quantities. Note the total amount that worked for you: it stays valid as long as you use the same water.

🪣 The most frequently used bottle

With hard mains water, pH- is used at every reservoir change and then as a top-up until the bicarbonates are neutralised, while pH+ is kept in reserve. With reverse-osmosis or rainwater, it is the opposite: pH+ is used at every fill, and pH- only after an over-correction. As both keep for 5 years after opening, the 1 L format will not go to waste; it suits very hard water or multiple tanks, while the 500 ml is sufficient for most home setups. Our article on pH regulation covers the approach in detail depending on your water type.

Technical specifications

What the duo contains

pH- corrector: 1 bottleNitric, phosphoric and citric acids. Yellowish liquid, pH 1.
pH+ corrector: 1 bottlePotassium carbonate 13%, silica 0.5%. Blue liquid, pH 12.
Growing methods: Hydro, coco and soilCompatible with any fertiliser, including other brands.
Target pH range: 5.5 to 6.5During rooting and growth. At pre-flowering and flowering stages, the target shifts to 6.4 to 6.8.

Use

First additions: 4 ml/50 L or 1 ml/10 LFor pH- and pH+ respectively, then in small doses while measuring.
Correction order: After fertilisersEvery fertiliser shifts the value as it dissolves. Mix first, then test: the effect is immediate.

Safety and storage

Classification of both: Danger, H314Causes severe skin burns and serious eye damage. Corrosive in category 1A for both.
Essential equipment: Gloves and gogglesSafety precautions P264 and P280, identical on both bottles.
Strictly prohibited: Never mix them togetherThe acid concentrate and the alkaline concentrate react vigorously and cancel each other out. Each one is added to water, never to the other.
Storage: Separate, upright, frost-freeStored separately, in their original packaging. Each keeps for 5 years after opening.

To budget for separately

pH measurement: Drop test kit or pH meterWithout it, the two bottles are dosed blind and corrections are made by guesswork.
Dosing syringe: Graduated, one per bottleTwo separate syringes prevent any trace of acid being brought back into the stock bottle.

4 further specifications are available in the detailed view.

In the box

1 bottle of pH- corrector in the chosen size, 500 ml or 1 L.
1 bottle of pH+ corrector in the same format.

H314 classifications, compositions, pH values and densities: French safety data sheets dated 22/11/2023 (pH-) and 08/01/2024 (pH+). Analyses, starting doses and storage: official French product sheets retrieved on 07/10/2026. Duo assembled by the shop from both references, in their original packaging.

The two correctors in the duo, side by side

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

You have both: which one will you use most at home? With tap water it is the pH- that gets used up; with rainwater it is the other. The second bottle is used to correct overshoots.

	Effect on the solution	Water concerned	The one you'll use most with tap water	The one you will use most with osmosis water	Active base	pH of concentrate	Liquid colour	Supplies phosphorus	Provides potassium	Silica source	Classified corrosive H314	Gloves and goggles must be worn	Never to be mixed with the other
pH- correctorYour choice	Lowers pH	Hard tap water	Yes	No	Nitric, phosphoric, citric acids	1	Yellowish	Yes	No	No	Yes	Yes	Yes
pH+ correctorYour choice	Raises pH	Reverse osmosis or rainwater	No	Yes	Potassium carbonate	12	Pale blue	No	Yes	Yes	Yes	Yes	Yes

pH- corrector

What each one does

Effect on the solutionLowers pH

Water concernedHard tap water

The one you'll use most with tap waterYes

The one you will use most with osmosis waterNo

Active baseNitric, phosphoric, citric acids

pH of concentrate1

Liquid colourYellowish

What it adds on top

Supplies phosphorusYes

Provides potassiumNo

Silica sourceNo

Safety

Classified corrosive H314Yes

Gloves and goggles must be wornYes

Never to be mixed with the otherYes

pH+ corrector

What each one does

Effect on the solutionRaises pH

Water concernedReverse osmosis or rainwater

The one you'll use most with tap waterNo

The one you will use most with osmosis waterYes

Active basePotassium carbonate

pH of concentrate12

Liquid colourPale blue

What it adds on top

Supplies phosphorusNo

Provides potassiumYes

Silica sourceYes

Safety

Classified corrosive H314Yes

Gloves and goggles must be wornYes

Never to be mixed with the otherYes

Compositions, pH values of the concentrates and classifications: French safety data sheets, version dated 22 November 2023 for pH- and 8 January 2024 for pH+. Descriptions taken from the 2025 French catalogue. Values recorded on 10 September 2026.

Documents & manuals

Safety data sheet for pH-, in French

Version dated 22 November 2023. H314 classification, composition, protective equipment and steps to take in the event 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 action to take in the event 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 growing stage, which these two correctors are used to maintain. A multilingual document, with French and English side by side.

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

8 questions

6 key questions, 8 in the detailed view

Do I need both, or just the pH-?

A single bottle is enough if your water never changes. With hard mains water all year round, the value does not drop on its own: only the pH- is ever needed, and the pH+ can be kept in reserve.

The duo becomes worthwhile as soon as your water source varies. Whether you collect rainwater for part of the year, switch to an RO unit, or blend the two, the direction of correction changes with the seasons and a single bottle is no longer sufficient. They work with any fertiliser, including other brands: a pH corrector acts on the water, not on the fertiliser.

What pH to aim for, and how to know which bottle to use?

5.5 to 6.5rooting and growth

6.4 to 6.8pre-flowering and flowering

With a two-part solution, what matters is knowing which end of the range you are drifting towards: above it, iron and manganese become less available and pH- is the correction; below 5.8, calcium uptake drops and pH+ is the answer. Always correct after adding your fertilisers, which are acidic: raising the plain water with pH+ and then watching the value fall once the fertilisers go in means using both bottles just to end up back where you started.

How much product is needed for 10 litres of water?

0.8 mlof pH- to start with

1 mlof pH+ to start with

These initial amounts correspond to the starting doses for each bottle: 4 ml of pH- per 50 litres and 1 ml of pH+ per 10 litres. Mix, measure, then adjust in small increments: pH- is worked in millilitre steps with hard water, and pH+ in tenth-of-a-millilitre steps with soft water.

If the value swings in both directions from one week to the next, look at your water rather than the bottles: hard water raises the pH until its bicarbonates have been neutralised, while soft water lets it drop because the fertilisers acidify it.

Are these two bottles safe to keep at home?

These are two corrosive concentrates, classified H314. Wear gloves and eye protection when measuring them out, and store them upright, sealed, and out of reach of children.

One rule must also be strictly observed: never pour one into the other, and never dip into the pH+ a syringe that has been used for the pH-. Each is added directly to the reservoir water. Once diluted to working concentrations, they present no hazard.

What is the difference compared to vinegar and bicarbonate?

Bicarbonate of soda does raise the pH, but it introduces sodium, which the plant has no nutritional use for: it stays in the reservoir, builds up with each correction, raises conductivity without providing any nutrition, and competes with potassium at the point of absorption. pH+ supplies potassium and silica instead.

On the acidic side, vinegar does lower the value, but it is an organic acid that the micro-organisms in the solution break down, so its effect fades quickly. pH- combines mineral acids that contribute nitrogen and phosphorus, along with citric acid to hold the value steady.

Are these pH adjusters suitable for an aquaponic pond?

Is a drop test sufficient for measuring both?

Which size to choose, 500 ml or 1 L?

The 2 x 500 ml is sufficient for one or two tanks with low-lime water. This is the format suited to the majority of domestic setups.
The 2 x 1 L is appropriate for very hard water, multiple tanks, or ongoing production, where each preparation uses noticeably more corrector.

Consumption depends far more on your water supply than on the volume being cultivated: your first correction will tell you which format to choose next time.

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pH correction duo: pH- and pH+

The summary