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Lab-Grade Instruments Designed Specifically For Growers

Lab-Grade Instruments Designed Specifically For Growers

Trouble

Reason

How to fix

Cannot calibrate

Incorrect calibration order

Power on the tester, calibrate pH 7 first, then pH 4. After pH 4 is calibrated, 

if you want to calibrate pH 7 again, you need to reboot the tester.

Poor quality standard solutions

Replace with fresh and clean standard calibration solutions made by

legitimate scientific instrument manufacturers.

Contaminated probe

Clean the probe with Apera’s cleaning solution or detergent water.

Aged probe

Replace the probe.

Dried-out probe

Soak the probe in the 3M KCL soaking solution for at least 1 hour.

Probe is not fully submerged in the

solution

Make sure the probe is fully immersed in the solution at least 1 inch deep.

Air bubbles around the sensor

Make a quick stir in the solution to remove air bubbles.

Reading is always slowly 

changing, won’t stabilize.

Contaminated probe

Clean the probe with Apera’s cleaning solution or detergent water.

Clogged junction

Clean the probe with Apera’s cleaning solution, then soak it in 3M KCL 

soaking solution overnight.

Aged probe

Replace the probe.

Testing pH of low iconic strength 

solutions like tap water, drinking water,

RO water

Be patient, wait for 2-5 minutes to reach a fully stabilized reading. If still not

stabilizing, add 1ml of 3M KCL solution to 1000ml of test solution.

Display similar readings in any

solutions or always display 7.0 pH

Broken probe

If you don’t find any visible damage of the probe and it’s within the 1-year

probe warranty, contact your point of purchase for warranty fulfillment;

If there is visible damage or the probe is more than 1-year old, replace the 

probe.

Reading keeps jumping

Probe is not fully submerged in the

solution

Make sure the probe is fully immersed in the solution at least 1 inch deep.

Air bubbles around the sensor

Make a quick stir in the solution to remove air bubbles.

Probe is not properly connected or the

pin connector is broken.

Check the probe’s connector, make sure it’s not broken and is correctly

connected. Align the probe and instrument correctly before plugging in. 

Never force it.

Ensure that the probe connector is not exposed in the air too long.

Calibration is successful, but 

reading is not accurate

Aged probe

Replace the probe.

Air bubbles around the sensor

Make a quick stir in the solution to remove air bubbles.

Clogged junction

Clean the probe with cleaning solution, then soak it in 3M KCL soaking

solution overnight

Comparison with other testers, test 

strips, or drop tests

To compare with other testers, make sure to perform a 2-point calibration 

for all testers in the same standards, then test a 3

rd

point. Whichever gives

more accurate reading in the 3

rd

point standard is the most accurate one. 

Test strips or drop tests’ accuracy is not comparable to pH meters’.

① Pull up the battery cap (might take some force).

② Slide the battery cover along the OPEN arrow to open the cover.

③ Open the battery cover.

④ Insert the batteries (ALL POSITIVE SIDES FACING UP)

⑤ Press down the battery cover and hold it.

⑥ Slide the battery cover along the LOCK arrow to lock the cover. 

⑦ Close the battery cap. Make sure to push it all the way down. 

     The tester’s waterproof rating may be compromised if the battery cap is not tightly closed.

Screw off the probe ring, unplug the old 

probe; plug in the new probe (make sure to 

align the connector's position properly), and 

screw on the probe ring.

Probes don’t last forever. Every probe will eventually 

age and fail even if you don't use it that often. The 

typical service life of GroStar probes is 18-24 months 

depending on the frequency of usage and how well 

you keep it clean and properly stored. 

We recommend replacing your probe at least every 

18 months to ensure the best accuracy. 

The nice thing about GroStar pens is that you can 

just buy a replacement probe instead of a whole new 

tester.

12.1

   Never store the probe in pure water such as tap water, RO water, distilled water, deionized water, etc.

Out of range reminder for pH

Out of range reminder for

 temperature

Out of range reminder for EC

12.2

   Never use your finger to touch the glass membrane or use other material to wipe it.

12.3

   Avoid testing in high (>113°F) or low temperature (<41°F) solutions as it will cause greater measurement error  

and damage to the probe. Test your samples and perform calibration close to room  temperature as much as 

possible.

12.4

   Never test oily liquids.

12.5

  Make sure the battery cap is completely closed with the O-ring. Otherwise, the waterproof rating could be 

compromised.

10

11

12

13

08

09

Battery Replacement

Probe Replacement

Notes

Troubleshooting Guide

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