# Should I pH my water before or after adding nutrients?

> Adjust pH after adding nutrients. Fertiliser salts, and silica most of all, change the solution's pH, so adjusting plain water first means adjusting twice. Mix everything, stir, then bring the feed to about pH 5.5-6.2 for hydro, 5.8-6.3 for coco or 6.2-6.8 for soil. In hydro, aerate a fresh mix 30-60 minutes before the final reading. Calibrate the meter first.

- Canonical: https://genetixbay.com/knowledge/answers/ph-before-or-after-nutrients.html
- Topic: pH and EC · Type: How-to
- Evidence: Established · Status: Draft: awaiting expert review
- Full article: [pH and nutrient availability: what pH really controls, by medium](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)
- Also asked as: Do I pH after adding nutrients? | When should I pH my water? | Should I pH first, then add nutes? | Why does my pH meter drift? | When should I replace my pH probe?
- 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

After. Nutrient salts change the [pH](https://genetixbay.com/knowledge/glossary/ph.md) of the water, so adjust once everything is mixed: about pH 5.5–6.2 for hydro, 5.8–6.3 for [coco](https://genetixbay.com/knowledge/glossary/coco-coir.md) and 6.2–6.8 for soil. In hydro, aerate a fresh mix for 30–60 minutes before the final adjustment. *Established.*

## Why

Fertiliser salts are acids and bases in their own right. Most nitrate-based feeds pull pH down when added to alkaline [tap water](https://genetixbay.com/knowledge/glossary/tap-water.md); [potassium silicate](https://genetixbay.com/knowledge/glossary/potassium-silicate.md) pushes it sharply up. Adjusting before mixing means adjusting twice and wasting acid.

Water pH matters less than you think. [Alkalinity](https://genetixbay.com/knowledge/glossary/alkalinity.md), the water's bicarbonate buffer, is what moves the [root zone](https://genetixbay.com/knowledge/glossary/root-zone.md) over time [1]. Measure the finished solution and the [runoff](https://genetixbay.com/knowledge/glossary/runoff.md), not the tap.

In [recirculating hydro](https://genetixbay.com/knowledge/glossary/recirculating-system.md), [carbon dioxide](https://genetixbay.com/knowledge/glossary/co2-enrichment.md) exchange and [nitrate](https://genetixbay.com/knowledge/glossary/nitrate.md) uptake keep moving pH after mixing [4], so a reading taken straight after stirring is provisional.

A reading is only as good as the meter. Calibrate with at least two fresh buffers, pH 7 then pH 4, and store the probe wet [2][3].

## The numbers

| Item | Target |
|---|---|
| Hydro feed | pH 5.5–6.2 |
| Coco feed | pH 5.8–6.3 (runoff 5.8–6.5) |
| Soil feed | pH 6.2–6.8 |
| Hydro settle time | 30–60 min aeration, then final adjust |
| Calibration | Two buffers (7 and 4), at least weekly |
| Probe slope, healthy | 95–102%; replace if stuck below ~90–95% |
| Probe life | ~1–2 years, stored wet |

## What to do

1. Calibrate the meter if it's been a week or readings seem odd.
2. Fill with water, add nutrients in order, stir.
3. Hydro: aerate 30–60 minutes.
4. Adjust pH in small doses, re-reading between.
5. Store the probe in storage solution or [pH 4 buffer](https://genetixbay.com/knowledge/glossary/calibration-solution.md).

*Safety:* gloves and eye protection when handling pH adjusters.

## Common mistakes

- Adjusting plain water, then adding nutrients.
- Trusting a pen that hasn't seen buffer in months.
- Storing the probe dry or in [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md).
- Reading pH in a cold sample with no [temperature compensation](https://genetixbay.com/knowledge/glossary/atc.md).

## Related

- Full article: [pH and nutrient availability](https://genetixbay.com/knowledge/ph-ec/ph-nutrient-availability.md)
- Articles: [meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)
- Answers: [how to adjust pH](https://genetixbay.com/knowledge/answers/how-to-adjust-ph.md) · [mixing order](https://genetixbay.com/knowledge/answers/order-to-mix-nutrients.md) · [drops vs meter](https://genetixbay.com/knowledge/answers/ph-drops-vs-ph-meter.md)
- Terms: [two-point calibration](https://genetixbay.com/knowledge/glossary/two-point-calibration.md) · [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md)

## Follow-up questions

**Why does my pH meter drift?** A pH meter drifts mainly because the glass membrane and reference junction age, and drying out, storage in pure water, biofilm and salt crusts speed that up. Slow readings that take over 30-60 seconds to settle point to a dirty junction or old probe. A two-point calibration with fresh pH 7 and pH 4 buffer corrects drift until the probe can't be adjusted.

**When should I replace my pH probe?** Replace a pH probe when it can no longer be adjusted to match fresh buffer, or when its slope stays below about 90-95% after cleaning; an offset beyond about 30 mV at pH 7 is another warning sign. Glass pH electrodes typically last about one to two years when stored wet in storage solution or buffer, never dry or in RO water.

**Should I measure pH of plain water at all?** Measuring plain water pH tells you little on its own, because tap water pH has much less effect on the root zone than its alkalinity. It is useful as a quick check that your meter reads sensibly, and RO or distilled water often reads unstable on cheap pens. Make decisions on the pH of the finished nutrient solution and the runoff.

## 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 University / NC Department of Agriculture and Consumer Services. The pour-through extraction procedure: a nutrient management tool for nursery crops. https://ncagr.gov/ncsu-pour-through-extraction-procedure/download
3. Mettler-Toledo. pH measurement and USP <791> (white paper). https://www.mt.com/my/en/home/library/white-papers/lab-analytical-instruments/pH-measurement-USP-791.html
4. Bugbee B, 2004. Nutrient management in recirculating hydroponic culture. Acta Horticulturae 648:99-112. https://www.ishs.org/ishs-article/648_12