APERA INSTRUMENTS / SX723 / AI477

pH plus conductivity-derived readings.
One portable meter, two purpose-built probes.

SX723 provides pH, conductivity, calculated TDS, salinity, resistivity and temperature for compatible water-solution work. The kit supplies a 201T-S pH/temperature electrode and a 2301T-S conductivity/temperature electrode, each with an 8-pin plug. Change electrodes for the measurement family, then select the conductivity-derived parameter on the meter.

Choose AI477 when you need acidity and ionic-conductivity information during the same field visit without carrying two meters. This is not simultaneous pH and conductivity measurement. The supplied conductivity cell is the 2301T-S, not the BNC/RCA 2301T-F, and no ORP or dissolved-oxygen electrode is included.

Switch probes, then select the parameter

Automatic electrode recognition changes the meter to pH when the 201T-S is connected and to conductivity when the 2301T-S is connected. In conductivity mode, hold the confirmation/backlight key to cycle through TDS, salinity, resistivity and conductivity, releasing it at the desired parameter. These are selected views, not four independently connected sensors or a simultaneous multi-parameter display.

A platinum-black conductivity cell with its own thermistor

The supplied 2301T-S has a POM body, K=1 cell constant and built-in 30 kΩ temperature sensor. Its locking 8-pin plug differs from the 2301T-F’s BNC/RCA arrangement. The conductivity range reaches the 200 mS/cm class, but the current specification table ends at 199.9 mS/cm. Confirm a different cell constant and exact probe compatibility before planning very-low-conductivity work.

Keep calculated readings tied to a method

TDS, salinity and resistivity are derived from the conductivity response rather than independent chemical assays. Reference temperature is selectable at 18, 20 or 25°C; the compensation coefficient adjusts from 0.00 to 9.99%/°C. Document these settings when comparing results. The exact SX723 manual does not document a user-adjustable TDS conversion-factor menu, so one is not promised here.

Know what this configuration supplies.

Nutrient-solution and general water checks

Measure pH and conductivity as complementary observations in compatible hydroponic or water-treatment samples. Rinse and switch probes between measurements. Conductivity responds to the combined ionic content, while pH describes acidity; neither independently identifies which nutrient or dissolved substance is present.

Process rinses and field comparisons

Use consistent vessels, immersion, mixing and temperature settings when comparing rinse stages or locations. For conductivity, brief stirring helps dislodge trapped bubbles at the cell. Keep a worksheet that links each separate pH and conductivity record to the same sample rather than assuming the meter saves them as a synchronized pair.

Know the limit of pure-water claims

The meter has low-conductivity compensation functions, but that does not make the stock pH electrode suitable for low-ionic-strength water. The 201T-S guide specifically warns about distilled or deionized-water pH testing. For demanding pure-water work, establish the correct specialist probe, cell constant, sampling arrangement and method before purchase.

Two measurement families.
Two different calibration routines.

Connect the 201T-S with the notch aligned to the meter socket. Push straight in while holding the metal ring, then tighten that ring. Do not rotate the black rubber cable sleeve. Remove the storage bottle without spilling its KCl, rinse the tip with distilled or deionized water, and gently remove excess rinse water without rubbing the glass membrane.

For the supplied USA buffers, begin with pH 7.00. Press CAL, immerse the electrode, stir briefly and hold it still. Wait until the stability symbol stays on, then confirm as directed by the manual. Rinse between solutions and continue with pH 4.00 and pH 10.01 for three-point calibration. Use fresh, separate portions and never return used buffer to the original bottle.

The meter supports one, two or three calibration points. Select buffers that bracket the expected samples; a new pH electrode requires three-point calibration. The USA set lists 1.68, 4.00, 7.00, 10.01 and 12.45; NIST lists 1.68, 4.01, 6.86, 9.18 and 12.45. A China series is also selectable. The current page’s “13 kinds” wording describes recognition, not thirteen calibration points or thirteen included bottles. Match the selected series to the actual bottle labels.

For conductivity, connect the 2301T-S, confirm K=1 and return to conductivity mode before pressing CAL. Rinse the cell, immerse it in the supplied 1413 µS/cm standard, stir briefly to release bubbles and wait for stability before confirming. SX723 uses one-point conductivity calibration. The probe’s general PDF suggests multi-point calibration for other instruments; that generic instruction does not add multi-point capability to SX723.

The exact meter manual lists USA conductivity standards of 84 µS/cm, 1413 µS/cm, 12.88 mS/cm and 111.9 mS/cm; its China series lists 146.6 µS/cm, 1408 µS/cm, 12.85 mS/cm and 111.3 mS/cm. Eight recognized standards across two series do not mean eight calibration points. Only one 50 mL bottle of 1413 µS/cm is listed in this kit. Choose a suitable standard for the sample range.

Different sensors need different storage.
KCl for pH, clean water for conductivity.

Rinse the 201T-S before and after each measurement, then return it to its cap with enough Apera 3M KCl storage solution to cover the sensing tip. Pure water is appropriate for rinsing, not for storing this pH electrode. Keep the bottle upright and renew contaminated storage solution. The gel reference electrolyte is not user-refillable.

The current 201T-S page specifies 0 to 13 pH and 0 to 60°C, while its PDF specifies 0 to 14 pH and 0 to 80°C. Treat the narrower current-page limits as the buying guide and confirm demanding applications before ordering. The PDF additionally cautions against prolonged use above 50°C, frequent strong acid or alkali measurements, low-ionic-strength water and liquids that attack the polycarbonate housing. A wide meter display does not remove those probe limitations.

Clean according to the exact electrode guide, using a treatment suitable for the contamination rather than abrasive scrubbing. Rehydrate and recalibrate after cleaning. Keep plugs dry, clean and protected when disconnected. The IP57 rating is an enclosure protection specification, not a promise that an exposed connector or glass sensing bulb can tolerate immersion, drops, solvents or unrestricted chemical exposure.

Store the 2301T-S conductivity sensor in its cap filled with clean distilled or deionized water, replacing contaminated water. Do not use the pH electrode’s KCl storage solution in this cap. Rinse before and after use, avoid rubbing the platinum-black cell and follow the probe guide for residue-specific cleaning. Conductivity ATC covers 0 to 50°C; the probe guide separately lists a wider operating-temperature limit. That wider limit does not extend the compensated measurement range.

Read the display. Check the measurement mode.

Use the physical controls for measurement, calibration and the documented record functions. Check units, temperature, calibration indicators and the selected parameter before assigning a result to a sample. Screen values in photographs are illustrative, not sample results. The model-specific record and output workflow is explained below.

Follow the exact parameter-specific calibration procedure, using the required standard, solution or calibration atmosphere. Temperature compensation does not make different sample temperatures, preparation methods or chemistry equivalent. Follow the model-specific meter and electrode instructions before extending the method to a new sample.

Current-page memory: 300 sets.
Manual storage is not a timed logger.

The current SX723 page specifies 300 stored sets. Its exact v3.0 PDF specifies 400 in both the technical table and save-data instructions, while a current gallery memory illustration says 200. This listing follows the current 300-set product specification and explicitly discloses the conflicting legacy sources. Confirm unit-specific capacity if the size of a field round depends on it.

The documented workflow is a short press to save a stable measurement and a long press to recall saved readings. Records contain serial number, value, unit and temperature. The exact manual does not document scheduled intervals, real-time-clock timestamps, USB transfer, computer software or a phone app. The backlight and power-off timers are not data-logging settings.

Keep sample name, collection time, connected probe and compensation settings in a separate worksheet, then transcribe required readings before clearing memory. A TDS record and a pH record are separate observations, even when taken from the same vessel. On-meter recall does not provide an audit trail or establish any regulatory or laboratory accreditation claim.