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Hanna HI-99121 Waterproof pH & temperature meter for direct measurement in soil

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The HI-99121 portable pH meter, together with HI-12923 pH electrode, is designed to measure pH in soil or soil slurries.

The HI-99121 is a lightweight, portable pH and temperature meter. It features a two button operation system and is simple to use. It has a waterproof and compact casing, large dual-line display, and automatic pH calibration at one or two points.


£586.50 (exc.VAT)
£703.80 (tax incl.)
Full Description Specification Manuals

Main features

  • Simultaneous pH and temperature measurements on a large dual-line LCD display
  • Automatic pH calibration at one or two points within two memorised buffer sets (standard or NIST)
  • Selectable temperature unit (°C or °F)
  • Electrode condition indicator
  • mV or pH measurement for electrode check
  • HI-12923 dedicated pH probe with integrated temperature sensor
  • Probe quick connect system
  • Battery life indication and low battery detection
  • Keystroke confirmation tone
  • Auto-off function
  • Waterproof casing IP67

About Soil pH

pH is the measure of the hydrogen ion concentration (H+). The pH scale goes from 0 (very acidic) to 14 (basic) with pH 7 being neutral. Soil can be acid, neutral or alkaline.

Most plants prefer a pH range from 5.5 to 7.5; but some species prefer more acid or alkaline soils. Nevertheless, every plant has a target for optimum growth.

pH strongly influences the availability of nutrients and the presence of micro-organisms and plants in the soil.

For example, fungi prefer acidic conditions whereas most bacteria, especially those supplying nutrients to the plants, have a preference for moderately acidic or slightly alkaline soils. In fact, in strongly acidic conditions, nitrogen fixing and the mineralisation of vegetable residual is reduced. Plants absorb the nutrients dissolved in the soil water and the nutrient solubility depends largely on the pH value. Hence, the availability of elements is different at varying pH levels.

Each plant needs elements in different qualities and this is the reason why each plant requires a particular range of pH to optimise its growth.

For example, iron, copper and manganese are not soluble in an alkaline environment. This means that plants needs these elements should theoretically be in an acidic type of soil. Nitrogen, phosphorus, potassium and sulphur, on the other hand, are readily available in a pH range close to neutrality.

Abnormal pH values may increase the concentration of toxic elements for plants. For example, a plant may not tolerate an excess of aluminium ions that may increase under acidic conditions. When pH values are too far from neutral conditions a less permeable and more compact soil may result.

Different naturally occurring minerals may affect soil pH in the same way.

Supplied with:

  • HI-12923 pH/temperature probe with conical tip, DIN Connector and 1m cable
  • HI-70004 pH 4.01 buffer (1 sachet)
  • HI-70007 pH 7.01 buffer (1 sachet)
  • HI-700663 cleaning solution for soil deposits (1 sachet)
  • HI-700664 cleaning solution for humus deposits (1 sachet)
  • HI-7051M soil sample preparation solution
  • HI-721319 auger for ground penetration, packed separately in a carton box
  • beaker (1)
  • 1.5 AAA alkaline batteries
  • Instrument quality certificate
  • Electrode quality certificate
  • Instruction manual

The electrode, auger & soil prep solution explained

HI-12923 has a conical rugged tip. It has a built-in temperature probe for temperature compensated pH readings and an integrated pre-amplifier to provide measurements impervious to noise and electrical interferences.

The HI-721319 auger for ground penetration is supplied to loosen the soil prior to any measurements being taken. The use of the auger is recommended to prevent scratching to the pH glass.

For best results, it is recommended that soil tests be carried out using a prepared soil slurry using the HI-7051 soil sample preparation solution, rather than direct ‘in the field’ measurements - although this is possible following the instructions and use of the included auger.

Optimum pH values for growers

Orchard plants, vegetables and herbaceous cultivations

Preferred pH Range

  • 4.5 to 6 pH - potatoes
  • 5 to 6.5 pH – Apples, rice
  • 5.5 to 6 pH – Sweet potatoes
  • 5.5 to 6.5 pH – Pomegranate, melon, soybean, tomatoes, watermelon
  • 5 to 7 pH – Orange
  • 5 to 7.5 pH - Strawberry
  • 5.5 to 7 pH – carrots, egg plant
  • 5.5 to 7.5 pH – cucumber, pumpkin
  • 6 to 7 pH – Apricot, Grapevine, lemon, barley, lettuce, oat, onion, pepper, wheat
  • 6 to 7.5 pH – Cherry , grapefruit, nectarine, peach, pear, plum, bean, Brussels sprouts, peas, spinach, sunflowers
  • 6.5 to 7.5 pH – Artichoke
  • 6 to 8 pH – Walnut, asparagus

Garden plants, flowers & house plants

  • Optimum growing pH between 4.5 and 8.

Read More

pH Range-2.00 to 16.00 pH
 Temperature Range-5.0 to 105.0°C / 23.0 to 221.0°F
pH Resolution0.01 pH
 Temperature Resolution0.1°C / 0.1°F
pH Accuracy±0.02 pH
 Temperature Accuracy±0.5°C (up to 60°C), ±1°C (outside);
±1.0°F (up to 140°F), ±2°F (outside)
pH Calibrationautomatic, 1 or 2 point with 2 sets of memorised buffer values
(pH 4.01 / 7.01 / 10.01 or pH 4.01 / 6.86 / 9.18)
Temperature CompensationAutomatic, -5 to 105°C (23 to 221°F)
pH ElectrodeHI 12923 preamplified pH and temperature probe with conical tip,
DIN connector and 1 m (3.3') cable (included) - The HI-12923 is limited to be used from 0 to 12 pH and from -5 to 70°C
Battery Type / Life3 x 1.5V AAA / approx. 1400 hours of continuous use:
auto-off after 8 minutes of non-use
Environment0 to 50°C (32 to 122°F); RH max 100%
Dimensions154 x 63 x 30 mm (5.9 x 3.1 x 1.4")
Case ingress protection ratingIP67

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