# pH Down

> pH Down is any acid used to lower solution pH, commonly phosphoric, nitric or sulfuric acid; each adds a nutrient, and all need gloves and eye protection.

- Canonical: https://genetixbay.com/knowledge/glossary/ph-down.html
- Also written: pH decreaser, pH minus, pH-, acid adjuster, pH down solution
- Glossary category: pH, EC and water · Evidence: Established
- Status: Draft: awaiting expert review · Updated: 2026-10-31
- Licence: CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/), attribute "GenetixBay cannabis glossary"

pH Down is the generic name for acids used to lower the [pH](https://genetixbay.com/knowledge/glossary/ph.md) of water or nutrient solutions. Common choices: [phosphoric acid](https://genetixbay.com/knowledge/glossary/phosphoric-acid.md) (adds phosphorus; the usual hobby product), [nitric acid](https://genetixbay.com/knowledge/glossary/nitric-acid.md) (adds [nitrate nitrogen](https://genetixbay.com/knowledge/glossary/nitrate.md); common in commercial hydro and favoured in flower when P is already high) and sulfuric acid (adds sulfur). Citric acid is sometimes used in organic setups, but microbes consume it, so pH drifts back quickly.

## In practice

How much you need depends mostly on the water's alkalinity, not its pH. Hard tap water with high bicarbonate needs far more acid than [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) at the same starting pH, because the acid first neutralises the bicarbonate. Langenfeld and Bugbee (2025) examined pH control in [recirculating](https://genetixbay.com/knowledge/glossary/recirculating-system.md) hydroponics using nitric acid and [ammonium nitrate](https://genetixbay.com/knowledge/glossary/ammonium-nitrate.md).

Add after nutrients, in small doses, mix well, wait, re-measure. Keep a log of millilitres per litre so the next mix is quick.

**Safety:** concentrated acids burn skin and eyes. Wear gloves and eye protection, always add acid to water, never water to acid, store away from bases and keep out of reach of children.

## Don't confuse with

- **Vinegar**: weak acetic acid; unstable and a poor choice in hydro.
- **Reducing alkalinity**: the real job of acid in [hard water](https://genetixbay.com/knowledge/glossary/general-hardness.md); pH follows.

## Related terms

[pH Up](https://genetixbay.com/knowledge/glossary/ph-up.md), [pH](https://genetixbay.com/knowledge/glossary/ph.md), [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), [Carbonate hardness](https://genetixbay.com/knowledge/glossary/carbonate-hardness.md)

## Read more

- [pH drift in hydro: why reservoir pH rises (and sometimes falls)](https://genetixbay.com/knowledge/ph-ec/ph-drift-hydro.md)
- [Water quality for cannabis: RO vs tap, alkalinity, bicarbonates and chloramine](https://genetixbay.com/knowledge/ph-ec/water-quality.md)

## Sources

1. Langenfeld NJ, Bugbee B. 2025. pH control in recirculating hydroponics with nitric acid and ammonium nitrate. HortScience 60(9):1555. https://journals.ashs.org/view/journals/hortsci/60/9/article-p1555.xml
2. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12