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EC and both ppm scales, with no pH sensor to maintain. GroStar GS3 Gen II combines its model-specific sensor setup with a practical calibration routine and TruRead session summaries.
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GS3-E is the official replacement for GroStar GS3 and is also compatible with GS4.
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APERA GROSTAR / GS3 / GEN II / AI103G
GS3 Gen II puts EC and the familiar 500/700 ppm scales into a focused liquid-testing pen. Its replaceable titanium sensor, single-point EC calibration and TruRead session summaries help keep routine nutrient-solution comparisons consistent.
Choose GS3 when feed strength is the question and you do not need pH in the same pen. Both ppm displays are calculated from conductivity; they are not two extra nutrient sensors.
0-10.0 EC
Conductivity range
EC is displayed in mS/cm
500 / 700
Two derived ppm scales
Match the scale on your feed chart
GS3-E
Replaceable titanium sensor
No pH sensor in the supplied setup
Choose by the measurement and the probes supplied. Each card opens that model’s product page; optional compatibility does not mean an extra probe comes in the box.
AI101G
Liquid pH
pH probe supplied; ORP head optional.
AI201G
Liquid pH + ORP kit
Two probes supplied; swap to read ORP.
AI102G
Moist soil/media pH
Spear, dibber and cleaning brush.
AI103G
Liquid EC / ppm
EC sensor supplied; no pH probe.
AI104G
Liquid pH + EC / ppm
Combo head supplied; ORP head optional.
AI204G
Combo + ORP kit
Combo and separate ORP heads supplied.
ONE SOLUTION. DIFFERENT CONVERSION SCALES.
Start with the conductivity. Apera’s worked example uses 2.6 mS/cm. The 500 and 700 displays apply different multipliers to that same EC; changing the scale does not change the nutrient solution.
2.6 mS/cm
The measured EC
1300 ppm
500 scale: 2.6 × 500
1820 ppm
700 scale: 2.6 × 700
Match the feed chart’s scale, or compare EC directly. This is a conversion example, not a recommended feed strength or dosing target.
GS3 pen with GS3-E titanium EC probe and cap, 2.77 EC calibration standard (50 mL), four installed AAA batteries, lanyard and instructions.
The supplied-fluid list is separate from optional compatibility: pH buffers, a pH sensor and KCl pH-storage solution are not supplied as part of this EC-only setup.
WHAT THIS MODEL IS BUILT TO ANSWER
Use EC to compare feed strength within an established grow routine. It reflects combined ionic conductivity, not the identity or amount of each nutrient.
Find out whether the recipe uses the 500 or 700 scale. Compare like with like or use EC rather than adjusting the reservoir because two scales show different numbers.
Use a repeatable rinse/sampling method and TruRead summaries when comparing multiple stable readings. The session summary is not a record-export feature.
Supplied probe: GS3-E / AI803G. The titanium EC element supplies the conductivity basis for both ppm scales.
Replaceability gives the worn sensor a maintenance path; it is not an unlimited service-life guarantee. Install, condition and calibrate the correct head according to its instructions.
A SESSION SUMMARY, NOT A CLOUD LOGGER
In the documented Gen II TruRead workflow, a reading that has stayed stable for seven seconds is recorded for the session. Review the average, maximum and minimum after collecting your measurements. Seven seconds of stability is not the same as a fixed seven-second sampling interval.
1.8 mS/cm
Illustrative minimum
1.9 mS/cm
Illustrative average
2.0 mS/cm
Illustrative maximum
The three illustrative values explain the summary; they do not prescribe a fixed sample count. The reviewed instructions do not establish retained history, timestamps or export. Use a suitable logger if those are requirements.
Calibrate at the manual’s single 2.77 EC point. It is 2.77 mS/cm, not a pH buffer or two separate ppm calibration points. The two ppm scales inherit the conductivity calibration.
Rinse between standards and samples to limit carryover. Remove excess water and bubbles, then wait for stability.
Use fresh, correct standards. A calibration reminder or electrode-condition display supports the routine; it does not replace checking the method.
Watch the manufacturer’s family tutorial alongside the current Gen II manual. The video is a practical family reference, not proof that every photographed control or accessory is identical across revisions.
Use the GS3 conductivity-only care routine: a wet cap for regular use and clean water to the fill line for storage beyond one month. Rinse after samples and clean as the manual directs. Do not copy the pH pens’ KCl storage into GS3.
They are different conversion scales. The same 2.6 mS/cm solution is 1300 ppm on the 500 scale and 1820 ppm on the 700 scale.
Check calibration solution, adequate immersion and bubbles at the sensor before changing the nutrient recipe. Rinse off carryover and wait for stability.
If the job is a cabled-probe water-testing workflow rather than a pocket grower pen, compare the alternatives below. These are separate instruments, not plug-in accessories or direct-soil replacements for GS3.
Alternative format: Hanna HI99300 portable liquid EC/TDS meter
Related workflow: Hanna HI98195 portable water pH/ORP/EC meter
No. The supplied GS3-E measures conductivity and temperature, with calculated 500/700 ppm displays. Choose GS4 if pH is needed in the supplied combo setup.
The kit supplies GS3 with its titanium GS3-E sensor, 2.77 EC standard, four installed AAA batteries, lanyard and instructions. pH buffers and pH KCl storage solution are not part of the GS3 workflow.
At 2.6 mS/cm, the 500 scale gives 2.6×500=1300 ppm and the 700 scale gives 2.6×700=1820 ppm. Match the feed chart’s scale or compare EC; the solution has not changed.
EC range is 0-10.0 mS/cm, resolution 0.1 EC and accuracy ±0.1 EC. The 500 scale covers 0-5000 ppm with 10 ppm resolution/±30 ppm accuracy; the 700 scale covers 0-7000 ppm with 10 ppm/±40 ppm.
The linked Gen II manual specifies one EC point at 2.77 EC. Do not copy the pH pens’ two-point workflow or treat 500 and 700 ppm scales as separate calibration standards.
The manual establishes stable-reading session collection and average/max/min, not persistent history, timestamps, USB, Bluetooth or export. Do not select it on the assumption that it is a field data logger.
The specified replacement is GS3-E, catalog AI803G, with a titanium-alloy conductivity sensor. Recalibrate after following the installation/conditioning instructions.
Do not borrow that pH-electrode routine. The GS3 manual uses a wet cap for regular use and clean water for longer storage. Rinse and clean the EC sensor appropriately, then recalibrate as needed.
Review the GS3 kit and specifications, then return to the price and ordering controls. Blue Tiger Scientific can help you match the measurement, sensor and routine before ordering.
APERA INSTRUMENTS, LLC warrants this instrument to be free from defects in material and workmanship and agree to repair or replace free of charge, at the option of APERA INSTRUMENTS, LLC, any malfunctioned or damaged product attributable to the responsibility of APERA INSTRUMENTS, LLC for a period of TWO YEARS for the instrument and ONE YEAR for the probe from the delivery.
This limited warranty does NOT cover any issues due to:
Use the current Gen II guide for controls, sampling and care. The US catalog adds family/probe/kit comparison; it is not a replacement for the operator instructions. Each card opens a PDF in a new tab.
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