# Buffering capacity

> Buffering capacity is how strongly a water, solution or medium resists pH change when acid or base is added; high capacity means stable but hard-to-move pH.

- Canonical: https://genetixbay.com/knowledge/glossary/buffering-capacity.html
- Also written: buffer capacity, pH buffering capacity, buffering power, acid-neutralising capacity, acid neutralizing capacity
- 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"

Buffering capacity is the amount of acid or base needed to change the [pH](https://genetixbay.com/knowledge/glossary/ph.md) of a solution or medium by a given amount. In water it comes mostly from bicarbonate and carbonate, measured as [alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md). In growing media it comes from organic matter, clay, lime and [cation exchange](https://genetixbay.com/knowledge/glossary/cation-exchange-capacity.md) sites: peat and soil buffer strongly, [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) moderately, [rockwool](https://genetixbay.com/knowledge/glossary/rockwool.md) and [clay pebbles](https://genetixbay.com/knowledge/glossary/clay-pebbles.md) hardly at all.

## In practice

High buffering capacity is a mixed blessing. Soil rich in organic matter keeps root-zone pH steady even when input pH is off, which is why soil growers need to adjust less. But water with high alkalinity takes a lot of acid to bring down and, over weeks, can push container media pH upwards.

Low buffering capacity is the RO-water and hydro problem: pH moves easily, so small additions overshoot and drift is fast. A small reservoir of [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md) with nutrients may drift 0.3–0.5 pH units in a day.

## Units and formula

For water, buffering capacity is usually reported as alkalinity in mg/L (ppm) as CaCO3, or as [carbonate hardness](https://genetixbay.com/knowledge/glossary/carbonate-hardness.md) in dKH.

## Don't confuse with

- **pH**: where the solution is; buffering capacity is how firmly it stays there.
- **Cation exchange capacity (CEC)**: a medium's ability to hold cations; related but not the same.

## Related terms

[Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), [pH buffer](https://genetixbay.com/knowledge/glossary/ph-buffer.md), [pH drift](https://genetixbay.com/knowledge/glossary/ph-drift.md), [Carbonate hardness](https://genetixbay.com/knowledge/glossary/carbonate-hardness.md), [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md)

## Read more

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

## Sources

1. Bugbee B. 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12
2. Abad M, Noguera P, Puchades R, Maquieira A, Noguera V. 2002. Physico-chemical and chemical properties of some coconut coir dusts for use as a peat substitute for containerised ornamental plants. Bioresource Technology 82(3):241-245. https://doi.org/10.1016/S0960-8524(01)00189-4