# How do I raise or lower the pH of my water?

> Lower pH with a mineral acid pH down (phosphoric, nitric or sulfuric) and raise it with potassium hydroxide or potassium silicate, after the nutrients are in. Add a few drops per 10 litres, stir, wait, re-read. In hydro, recheck after 15-30 minutes of circulation. A steady rise of 0.1-0.4 pH per day in a healthy reservoir is normal, from nitrate uptake and aeration stripping CO2.

- Canonical: https://genetixbay.com/knowledge/answers/how-to-adjust-ph.html
- Topic: pH and EC · Type: How-to
- Evidence: Established · Status: Draft: awaiting expert review
- Full article: [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md)
- Also asked as: How much pH down should I use? | How do I lower pH? | How do I raise pH? | Why does my hydro pH keep going up? | Does an air stone raise pH?
- Updated: 2026-10-31 · Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay Knowledge Base (genetixbay.com/knowledge)"

## Short answer

Lower [pH](https://genetixbay.com/knowledge/glossary/ph.md) with a mineral-acid pH down (phosphoric, nitric or sulfuric acid); raise it with potassium hydroxide or [potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md). Adjust after the nutrients are in, a few drops per 10 litres at a time, stirring and re-reading between doses. In hydro, recheck after 15–30 minutes of circulation. *Established.*

## Why

Every acid and base is also a nutrient. [Phosphoric acid](https://genetixbay.com/knowledge/glossary/phosphoric-acid.md) adds phosphorus, nitric adds nitrogen, sulfuric adds [sulfur](https://genetixbay.com/knowledge/glossary/sulfur.md), and potassium hydroxide adds potassium [2]. Small doses don't matter; daily heavy dosing does, so count them.

[Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md) is what fights you. Bicarbonate in [hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md) neutralises acid, so the same dose of pH down moves soft water a long way and hard water barely at all [1]. One meq/L of acid neutralises one meq/L of alkalinity [1][2].

Hydro pH rises on its own. Plants take up [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md), an anion, and release hydroxide or bicarbonate to stay balanced, so a nitrate-fed reservoir drifts upward as plants grow [3][4]. Aeration strips dissolved [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) and pushes pH up in the first hours after mixing.

## The numbers

| Goal | Use | Adds |
|---|---|---|
| Lower pH, veg | Nitric or phosphoric acid | N or P |
| Lower pH, flower / [N taper](https://genetixbay.com/knowledge/glossary/nitrogen-taper.md) | Phosphoric or sulfuric acid | P or S |
| Raise pH | Potassium hydroxide | K |
| Raise pH, with [silica](https://genetixbay.com/knowledge/glossary/silica.md) | Potassium silicate | K, Si |
| Normal hydro drift | 0.1–0.4 pH/day upward | n/a |
| Treat water alkalinity above | 100–150 mg/L as CaCO₃ (2–3 meq/L) | n/a |

## What to do

1. Calibrate the meter.
2. Mix all nutrients first; in hydro, aerate 30–60 minutes.
3. Add adjuster a few drops per 10 L, stir, wait 1–2 minutes, re-read.
4. Hydro: recheck after 15–30 minutes of circulation.
5. Let pH ride within the band (5.5–6.2 hydro, 5.8–6.3 [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md)); reset only when it leaves.
6. If pH won't hold, get a water report and treat alkalinity.

*Safety:* concentrated acids and hydroxides burn skin and eyes. Gloves and goggles, good ventilation, and always add acid to water, never water to acid.

## Common mistakes

- Overshooting, then correcting back and forth.
- Adjusting before nutrients go in.
- Chasing normal upward drift several times a day.
- Using [nitric acid](https://genetixbay.com/knowledge/glossary/nitric-acid.md) during a nitrogen taper.

## Related

- Full article: [Water quality: alkalinity and acids](https://genetixbay.com/knowledge/ph-ec/water-quality.md)
- Articles: [pH drift in hydro](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md)
- Answers: [pH before or after nutrients](https://genetixbay.com/knowledge/answers/ph-before-or-after-nutrients.md) · [vinegar or lemon?](https://genetixbay.com/knowledge/answers/vinegar-or-lemon-to-lower-ph.md)
- Terms: [pH down](https://genetixbay.com/knowledge/glossary/ph-down.md) · [pH up](https://genetixbay.com/knowledge/glossary/ph-up.md) · [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md)

## Follow-up questions

**Why does my hydro pH keep going up?** Hydro reservoir pH keeps going up mainly because cannabis absorbs nitrate faster than cations and releases hydroxide or bicarbonate to stay electrically balanced. Aeration stripping carbon dioxide, alkaline top-up water and algae in a lit reservoir add to it. A steady climb of about 0.1-0.4 pH per day with falling EC is normal; reset it when it leaves 5.5-6.2.

**Does an air stone raise pH?** Yes, an air stone can raise reservoir pH, because strong aeration strips dissolved carbon dioxide, which otherwise forms carbonic acid. The effect is largest in the first hours after mixing, especially with carbonated groundwater, and depends on the water's alkalinity. Aerate a fresh mix for 30-60 minutes before the final pH adjustment so the reading settles.

**Why does my pH bounce back after I add pH down?** pH bounces back after pH down when the water is high in alkalinity: bicarbonate buffers the acid, and as carbon dioxide leaves the solution the pH climbs again. Get a water report; above about 100-150 mg/L alkalinity as calcium carbonate, neutralise most of it with acid, leaving roughly 0.5-1 meq/L as a buffer in hydro.

## Sources

1. Lopez RG, Mickelbart MV, Pasian C. Alkalinity management in soilless substrates. Purdue Extension HO-242-W. https://www.extension.purdue.edu/extmedia/HO/HO-242-W.pdf
2. NC State Extension. Producing conventional tobacco transplants in greenhouses: water quality. https://content.ces.ncsu.edu/producing-conventional-tobacco-transplants-in-greenhouses-water-quality
3. Bugbee B, 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12
4. Marschner P (ed.), 2012. Marschner's Mineral Nutrition of Higher Plants, 3rd ed. Academic Press. https://doi.org/10.1016/C2009-0-63043-9