# What meters do I actually need for growing?

> For a first grow you need three meters: a pH meter calibrated with pH 7 and pH 4 buffers, an EC meter checked against a 1.413 mS/cm standard, and a thermo-hygrometer with min/max memory, salt-tested for accuracy. An IR thermometer is a cheap fourth. A PAR meter is worth it once you grow regularly. A meter you don't calibrate is worse than none.

- Canonical: https://genetixbay.com/knowledge/answers/meters-you-need-for-growing.html
- Topic: Equipment · Type: How-to
- Evidence: Established · Status: Draft: awaiting expert review
- Full article: [pH and EC meter calibration: buffers, slope, storage and when to replace a probe](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)
- Also asked as: What are the essential grow meters? | Do I need a pH pen, EC meter and hygrometer? | Do I need a PAR meter? | Which meters are worth buying for a first grow?
- 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

You need three: a **[pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md)** (calibrated with [pH](https://genetixbay.com/knowledge/glossary/ph.md) 7 and pH 4 buffers), an **[EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md)** (checked against **1.413 [mS/cm](https://genetixbay.com/knowledge/glossary/ms-cm.md)**) and a **thermo-hygrometer** with min/max memory (salt-tested). An **[IR thermometer](https://genetixbay.com/knowledge/glossary/ir-thermometer.md)** is a cheap fourth; a **[PAR](https://genetixbay.com/knowledge/glossary/par.md) meter** pays off once you grow regularly. *Established* for calibration practice.

## Why

pH controls which nutrients roots can take up. A pH meter is only as good as its last calibration: two fresh buffers that bracket your readings, at least weekly [1].

[EC](https://genetixbay.com/knowledge/glossary/ec.md) tells you how strong the feed and [runoff](https://genetixbay.com/knowledge/glossary/runoff.md) are. EC meters drift less than pH probes, but still need checking against a standard and after drops or battery changes [2]. [TDS](https://genetixbay.com/knowledge/glossary/tds.md) meters show the same reading converted to ppm by a factor that varies.

Temperature and humidity drive [VPD](https://genetixbay.com/knowledge/glossary/vpd.md) and disease risk. Min/max memory catches the lights-off humidity spike you never see. A salt test shows whether the [RH](https://genetixbay.com/knowledge/glossary/relative-humidity.md) reading is honest [3].

Light is the biggest yield lever indoors [4]. A quantum meter turns guessing into setting.

## The numbers

| Meter | Must-have? | Check against | How often |
|---|---|---|---|
| pH meter | yes ([coco](https://genetixbay.com/knowledge/glossary/coco-coir.md)/hydro); strongly advised (soil) | pH 7.00 + 4.01 buffers | weekly, before decisions |
| EC meter | yes | 1.413 mS/cm standard | monthly, after drops |
| Thermo-hygrometer, min/max | yes | salt test, ~75 % RH | every few months |
| IR thermometer | useful | emissivity ~0.95 | — |
| Quantum (PAR) meter | later | — | — |
| [Jeweller's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md), 60× | yes, at harvest | — | — |
| pH probe life | | | ~1–2 years stored wet |

## What to do

1. Buy pH, EC and thermo-hygrometer first; buffers and [EC standard](https://genetixbay.com/knowledge/glossary/calibration-solution.md) with them.
2. Calibrate pH with pH 7, then pH 4; re-read pH 7 (within ±0.05).
3. Store the pH probe wet in storage solution, never in [RO water](https://genetixbay.com/knowledge/glossary/ro-water.md).
4. Salt-test the hygrometer before trusting it.
5. Log readings in your journal every time.
6. Add an IR thermometer, then a PAR meter as you scale up.

## Common mistakes

- Never calibrating the pH pen.
- Storing the probe dry.
- Reading ppm off a TDS meter without knowing its scale.
- One hygrometer on the floor, far from the canopy.

## Related

- Full article: [pH and EC meter calibration](https://genetixbay.com/knowledge/ph-ec/meter-calibration.md)
- [How do I check if my hygrometer is accurate?](https://genetixbay.com/knowledge/answers/calibrate-a-hygrometer.md)
- [How can I measure PPFD without a PAR meter?](https://genetixbay.com/knowledge/answers/measure-ppfd-without-a-par-meter.md)
- [Is a TDS meter the same as an EC meter?](https://genetixbay.com/knowledge/answers/tds-meter-vs-ec-meter.md)
- Terms: [pH meter](https://genetixbay.com/knowledge/glossary/ph-meter.md) · [EC meter](https://genetixbay.com/knowledge/glossary/ec-meter.md) · [jeweller's loupe](https://genetixbay.com/knowledge/glossary/jewelers-loupe.md)

## Follow-up questions

**Do I need a pH meter for soil?** For quality living or amended soil, a pH meter is useful but less critical, because soil buffers pH and runs at 6.2–6.8. For coco and hydro, where pH should be 5.5–6.5 and drifts quickly, a calibrated pH meter is essential. Either way, calibrate with fresh pH 7 and pH 4 buffers at least weekly and store the glass probe wet, never dry.

**Is a TDS meter good enough instead of an EC meter?** A TDS meter measures the same thing as an EC meter, electrical conductivity, then multiplies it by a conversion factor to show ppm. The factor varies, commonly 500 or 700, so two TDS meters can show different ppm for the same solution. Read or convert to EC in mS/cm, which is unambiguous, and check the meter against a 1.413 mS/cm standard.

**How long does a pH probe last?** A glass pH probe typically lasts about one to two years when stored wet in storage solution or pH 4 or 7 buffer. Storing it dry or in RO water shortens its life. Replace the probe when it can no longer be adjusted to match buffer, or when its slope stays below about 90–95 % after cleaning.

## Sources

1. 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
2. Prasad L, Meehan M. Using electrical conductivity and total dissolved solids meters to field test water quality. NDSU Extension WQ1923 (rev. 2025). https://www.ndsu.edu/agriculture/extension/publications/using-electrical-conductivity-and-total-dissolved-solids-meters-field-test
3. Greenspan L, 1977. Humidity fixed points of binary saturated aqueous solutions. Journal of Research of the National Bureau of Standards 81A(1):89–96. https://doi.org/10.6028/jres.081A.011
4. Rodriguez-Morrison V, Llewellyn D, Zheng Y, 2021. Cannabis yield, potency, and leaf photosynthesis respond differently to increasing light levels in an indoor environment. Frontiers in Plant Science 12:646020. https://doi.org/10.3389/fpls.2021.646020