All pH meters need to be calibrated on a regular basis; as time passes by and with frequent use your pH meter it will lose calibration. You will also find that as the batteries get older your meter will loose calibration. Keeping your meter calibrated will help keep your plants in good health and at optimal growth.

Your method of calibration will depend on what type of meter you own. pH meters require that you calibrate the meter with two pH solutions, pH 7 (neutral) and pH 4 (acidic). If you use your pH meter every day it is advisable to calibrate your meter once a week. To calibrate your meter you will need three clean glass/plastic containers that can hold sufficient solution to immerse the pH probe. One container will hold water for rinsing the probe, another container for the pH 7 solution and the last container for the pH 4 solution. Before you calibrate your meter do a visual inspection of the meter. Check for cracks on the meter, algae or salt deposits on the probe or any matter that shouldn't be on the probe. If there is algae or salt deposits on the probe clean it with a moist cotton swab. Once this has been done you are ready to calibrate your pH meter.

Hanna Checker 1 (HI98103)

1. Rinse probe in water and briefly shake off excess.
2. Switch the meter on.
3. Place probe into pH 7 solution and allow the pH reading to settle.
4. Adjust pH 7 screw on the top side of the meter until the meter reads 7.
5. Rinse probe again in water and shake.
6. Place probe into pH 4 solution and allow the pH reading to settle.
7. Adjust the pH 4/10 screw on the top side of the meter until the meter reads 4.
8. Your pH meter is now calibrated.

Hanna pHep 4 & pHep 5 (HI98127 & HI98128)

1. Rinse probe in water and briefly shake off excess.
2. Press the MODE button to turn meter on.
3. Place probe into pH 7 solution and allow the pH reading to settle.
4. Press the MODE button again to "turn the meter off" BUT keep holding the button down until the screen goes from "OFF" to "CAL". Immediately release the MODE button. "7" will appear on the screen and "cal" will flash on the bottom left corner. (The meter is now calibrating pH 7).
5. Once the meter has finished calibrating for pH 7 the screen will change from "7" to "4". At this point take the meter out of the pH 7 solution and rinse the probe quickly in the water, briefly shake off excess, and then place it directly into the pH 4 solution. Swirl the probe in the solution for a few seconds.
6. The screen will read "4" and "cal" will flash at the bottom left corner of the screen. (The meter is now calibrating pH 4).
7. Once the calibration sequence has been completed the screen will flash "OK" and go directly into reading in the pH mode.

Hanna Combo Meter (HI98129)

1. Rinse probe in water and briefly shake off excess.
2. Press the MODE button to turn the meter on.
3. If the meter is reading in EC or pH press the SET/HOLD button until the meter is reading in pH mode.
4. Place probe into pH 7 solution and allow the pH reading to settle.
5. Press the MODE button again to "turn the meter off" BUT keep holding the button down until the screen goes from "OFF" to "CAL". Immediately release the MODE button. "7" will appear on the screen and "cal" will flash on the bottom left corner. (The meter is now calibrating pH 7).
6. Once the meter has finished calibrating for pH 7 the screen will change from "7" to "4". At this point take the meter out of the pH 7 solution and rinse the probe quickly in the water, briefly shake off excess, and then place it directly into the pH 4 solution. Swirl the probe in the solution for a few seconds.
7. The screen will read "4" and "cal" will flash at the bottom left corner of the screen. (The meter is now calibrating pH 4).
8. Once the calibration sequence has been completed the screen will flash "OK" and go directly into reading in the pH mode.
9. If by mistake you hold the MODE button down to long while trying to calibrate and it goes into TEMP just press the MODE button until you get back to the reading mode. If you press the SET/HOLD button while the meter is in the TEMP or CONV modes you could alter the settings of your meter.

Hanna pH Gro’Chek (HI981408)

1. Rinse pH and grounding probes in water and briefly shake off excess.
2. Place pH and grounding probes into pH 7 solution and allow the pH reading to settle.
3. Adjust the pH 7 screw on the face of the meter until the meter reads "7".
4. Rinse the pH and grounding probes in water and shake.
5. Place pH and grounding probe into pH 4 solution and allow the pH reading to settle.
6. Adjust the pH 4 screw on the face of the meter until the meter reads "4".
7. The pH calibration is now complete.

Hanna Gro’Chek Portable Meter (HI9813)

1. Rinse probe in water and briefly shake off excess.
2. Switch the meter on.
3. Place probe into pH 7 solution and allow the pH reading to settle.
4. Adjust the pH dial on the face of the meter until the meter reads "7".
5. Once this has been done the calibration is complete.

Oakton pH Waterproof Tester 1 & 2

1. Rinse probe in water and briefly shake off excess.
2. Switch the meter on.
3. Place probe into pH 7 solution and allow the pH reading to settle.
4. Press the CAL button. "CA" will flash briefly and then the pH reading will flash.
5. Press the HOLD/CON button. This will calibrate the meter to pH 7.
6. Rinse probe in water and shake.
7. Place probe into pH 4 solution and allow the pH reading to settle.
8. Press the CAL button. "CA" will flash briefly and then the pH reading will flash.
9. Press the HOLD/CON button. This will calibrate the meter to pH 4.
10. The meter is now calibrated.

Always remember to keep the pH probe moist when not in use. It is best to use storage solution, otherwise use pH 4 solution. Only place storage solution in the well of the cap if you are using the Hanna Combo Meter (HI98129). It's not good to store the EC/TDS/CF/PPM probe in a storage solution; keep it dry. Never reuse your calibration solutions. Never pour your used calibration solutions back into the calibration solution bottles; this will contaminate the unused solution.

Your pH meter must be recalibrated every time you change the batteries. If the pH meter is a waterproof meter and you change the batteries be careful not to damage and of the O-rings or gaskets as this will allow water enter the meter causing damage. If the O-rings are damaged or lost and water/fluids get into the meter the warranty will become void.

Basically what these meters do is measure the flow of electrical current between the two metal posts in the probe. The more salts/nutrients that are in the water, the higher the reading. A TDS/PPM/EC meter needs to be regularly calibrated. If the meter is used daily then the meter should be calibrated weekly. If the meter is used less than daily then it should be calibrated once every two to three weeks. You don’t want to leave it much longer than this because as the battery life decreases the meter looses its calibration. Every time you replace the batteries on your meter or even take the batteries out of your meter you should recalibrate. You should check the meter regularly for cracks and salt deposits on the electrode. Always allow the calibration solution to warm up to room temperature, especially if the solution is stored in the refrigerator.

The calibration method of your TDS/PPM/EC meter will depend on what model you have.

Hanna Primo TDS Tester
Please Note: This meter requires calibration solution 1382ppm.

1. Place electrode into clean water to rinse it.
2. Shake off excess water
3. Switch the meter on.
4. Place meter into calibration solution 1382ppm, ensure that the calibration solution covers the probe between the “MIN” and “MAX” marks that is marked on the probe.
5. Press “ON”/”OFF” button, but keep pressing the button until “CAL” appears on the screen then release the button.
6. The meter will then flash “1382” on the screen, keep the probe in the solution until the meter has calibrated itself (the meter will cease flashing “1382” and will now be in the reading mode).
7. Your meter is now calibrated.

Hanna TDS Tester (DiST1 / HI98300)

8. Place electrode into clean water to rinse it.
9. Shake off excess water
10. Place meter into calibration solution (i.e. 1500ppm or 989ppm).
11. Turn the calibration screw until the meter reads the same as the calibration solution.
12. Your meter is now calibrated.

Hanna EC/TDS/Temp Waterproof Tester (DiST5 / HI98311)

1. This meter can be calibrated using either PPM or EC. If you are using Genesis calibration solution by Green Air to calibrate your Hanna HI98311 meter, you will need to change the conversion factor to correctly your calibrate meter. See “Changing the Calibration Factor for Hanna Meters” to do this correctly.
2. Place electrode into clean water to rinse it.
3. Shake off excess water.
4. Make sure that the meter is in the ppm reading mode and not in the pH or μS (EC)
5. Place meter into calibration solution (i.e. 1500ppm (0.7 conversion factor)).
6. Press the MODE button and keep holding down the button until CAL appears on the screen.
7. Release the MODE button
8. The meter will now display the calibration solution that is required to calibrate the meter. “CAL” will also flash on the meter screen during calibration. DO NOT USE ANY OTHER SOLUTION OTHER THAN WHAT IS DISPLAYED ON THE METER SCREEN TO CALIBRATE YOUR METER.
9. Once your meter is calibrated then it will go back into ppm reading with the solution temperature just below the ppm reading.
10. Your meter is now calibrated.

Hanna pH/EC/TDS/Temp Waterproof Tester (HI98129)

1. This meter can be calibrated using either PPM or EC. If you are using Genesis calibration solution by Green Air to calibrate your Hanna HI98311 meter, you will need to change the conversion factor to correctly your calibrate meter. See “Changing the Calibration Factor for Hanna Meters” to do this correctly.
2. Place electrode into clean water to rinse it.
3. Shake off excess water.
4. Make sure that the meter is in the ppm reading mode and not in the pH or μS (EC)
5. Place meter into calibration solution (i.e. 1500ppm (0.7 conversion factor)).
6. Press the MODE button and keep holding down the button until CAL appears on the screen.
7. Release the MODE button
8. The meter will now display the calibration solution that is required to calibrate the meter. “CAL” will also flash on the meter screen during calibration. DO NOT USE ANY OTHER SOLUTION OTHER THAN WHAT IS DISPLAYED ON THE METER SCREEN TO CALIBRATE YOUR METER.
9. Once your meter is calibrated then it will go back into ppm reading with the solution temperature just below the ppm reading.
10. Your meter is now calibrated.

Hanna Gro'Chek Portable pH/TDS/EC Meter (HI9813-0)

1. These meters are easy to calibrate.
2. Place electrode into clean water to rinse it.
3. Shake off excess water.
4. Press the PPM button to get the meter into ppm mode.
5. Place the ppm probe into the ppm calibration solution.
6. Adjust the PPM dial until the ppm reading on the meter is the same as that for the solution.
7. Your meter is now calibrated.

Hanna Gro'Chek Portable pH/TDS/EC/°C Meter w/Cal-Check Feature (HI9813-6)

1. These meters are easy to calibrate.
2. Place electrode into clean water to rinse it.
3. Shake off excess water.
4. Press the PPM button to get the meter into ppm mode.
5. Place the ppm probe into the ppm calibration solution.
6. Adjust the PPM dial until the ppm reading on the meter is the same as that for the solution.
7. Your meter is now calibrated.
8. Nutra-Dip Continuous Tri Meter (pH/TDS/Temp)
9. This meter is easy to calibrate.
10. Place electrode into clean water to rinse it.
11. Shake off excess water.
12. Place the ppm probe into the ppm calibration solution.
13. Adjust the PPM adjustment screw until the ppm reading on the meter is the same as that for the solution.
14. Your meter is now calibrated.

Oakton Waterproof TDS Tester – Low

1. The calibration screw for these meters is found next to the batteries in the battery compartment.
2. Place electrode into clean water to rinse it.
3. Shake off excess water.
4. Place the ppm probe into the ppm calibration solution.
5. Adjust the PPM screw in the battery compartment until the ppm reading on the meter is the same as that for the solution.
6. Your meter is now calibrated.

Changing the Calibration Factor for Hanna Meters (HI98311 and HI98129)

1. To change the conversion factor on these meters make sure the meter is reading in ppm mode.
2. Hold down the MODE button until TEMP appears on the screen. Before TEMP appears on the screen you will notice that CAL will appear first TEMP will appear after this.
3. At this point if you press the hold button you will be able to change you meter’s reading from °C to °F.
4. Press the MODE button, the conversion factor will now appear. It should read 0.5; press the hold button until it reads 0.7.
This will be the correct conversion factor for your meters if you are using the Genesis calibration solutions.
5. Press MODE button, the Beta factor will appear. DO NOT CHANGE THIS, it should remain at 1.9.
6. Press MODE button again until your meter returns back to the ppm reading.
7. Your Hanna meter is now ready to be calibrated using the Genesis calibration solutions.

Up is potassium hydroxide and pH Down is phosphoric acid (commercial growers will sometimes also use Nitric acid and Sulfuric acid). Customers who use tap water will normally need to use pH down to balance the pH of their nutrient solution. Tap water tends to have a lot of carbonates which tends to buffer tap water at a higher pH. Customers who use RO water will need to use pH Up as the reverse osmosis strips the tap water of all the carbonates, thus leaving the water with no buffering ability. The nutrients the growers use to feed their plants is acidic, and once the grower has applied all the required nutrients and enhancers the reservoir pH can be below 5. This is too low for plants; thus pH Up needs to be used in order to raise the pH to 6. Customers using both pH Up and Down should take care when using these products as both are very concentrated. Only small amounts should be used at a time until the customer becomes familiar with the products.

Different plants require different strengths of nutrient solution, e.g. lettuce cannot be fed the same nutrient strength as tomatoes.

Click here for a general guide and can be used for most plants

Plants should never be subjected to a sudden increase of more than 200ppm in the nutrient solution from one watering to the next. The transition from one growth stage to the next should take place over a few days. Clones and seedling should always be fed a low ppm (nutrient strength) in the beginning. Over the next few days the ppm’s can be increased up to 800ppm. Clones that are subjected to a ppm strength of 800ppm straight after transplanting will go into stress and shock. Clones and seedlings should always be kept for at least one week in the vegetative stage before attempting to put the plants into the stress of flowering. This gives the plant some time to acclimate to its new environment and also gives the grower a chance to gradually increase the nutrient strength.

pH Meter

Always remember to keep the pH probe moist when not in use. It is best to use pH Electrode Storage Solution; if you have run out of storage solution you can use pH 4 solution as an alternative. For the Hanna HI98129 black combo meter, place storage solution in the well of the cap that the pH electrode (not the TDS electrode) rests in. It is not advisable to store the EC/TDS/CF/PPM probe in any storage solution.

TDS Meter

The best way to store your TDS meter is to keep it clean and dry. TDS meters do not require any storage solutions. DO NOT store the TDS meter in distilled water.

For long term storage, make sure that the batteries are removed from the meter as leaking batteries will corrode the circuit board rendering the meter useless. None of our meters’ warranty covers leaking battery damage. For long term storage of the pH meter it is best if the probe is stored in sufficient storage solution; if the solution evaporates then the pH probe will dry out.

1:2 Dilution Method

1. Mix 3 oz. of soil with 6 oz. of distilled water
2. Let mixture stand for 15 to 20 minutes
3. Filter liquid into clean cup
4. Take reading