pH and EC meter problem

[dodidoki]

I need help.Can anyone give me a good advice for getting correct devices???? These ones are all calibrated, stored in KCl, merged into the same solution...even the showed temps are not the same.....

 

[wongwong]

What means by calibrated? freshly calibrated with pH buffer?weekly/monthly?
Self read from pH buffer which probe give you closer value?
5.92 vs 6.23 indeed do not differ much if in mininal buffering system
fertilizer often get some precipitate/ sticky organics that stick to probe head drifting reading, some battery-powered one even get the reading drift when the battery voltage drops ..........&avoid playing with something too alkaline, it ruin the probe quite fast

 

[Ray]

Maybe the thermistor in one is a bit off. Do you have a way to adjust the temperature readout to a known value? Some meters have automatic temperature compensation, while others require a manual adjustment.

 

[dodidoki]

Thanks, i bought a better device, Milwaukee mw101 pro with temp. compensation.I will get in on Monday.

 

[dodidoki]

What means by calibrated? freshly calibrated with pH buffer?weekly/monthly?
Self read from pH buffer which probe give you closer value?
5.92 vs 6.23 indeed do not differ much if in mininal buffering system
fertilizer often get some precipitate/ sticky organics that stick to probe head drifting reading, some battery-powered one even get the reading drift when the battery voltage drops ..........&avoid playing with something too alkaline, it ruin the probe quite fast

Yes, new devices, freshly calibrated with buffers, autamaticly calibrate if merged into buffer.

 

[katzenhai2]

What is the best way to test the pH value of substrate? Run water through it and test that or take some substrate, crush it and then test the water? Won't the pH be lower if I run more or less water through the pot? Or what would be more accurate: running water through the pot or immersing the pot in water for a while?

 

[Ray]

The tried and true "pour-through" test is pretty reliable:

• Water the plant thoroughly, drenching the potting medium with the solution of your choice.
• Wait 60 minutes for the pot to fully drain and for the “pot chemistry” to come to equilibrium.
• Trickle enough pure water (distilled is best) evenly over the surface of the medium to collect about 50 ml (a shot glass) of the drainage.
• Test the pH of the collected liquid. That is representative of what the plant experiences.

 

[terryros]

I am starting to think that the pour-through procedure is better for identifying if your media is retaining salts. You get this information from doing the process that Ray described but testing the EC. If the EC of the pour-through fluid is distinctly higher than the EC of the fertilizing solution, something is accumulating. Obviously, the retained salts are going to impact the pH as well.

 

[Ray]

All of the above.

 

[katzenhai2]

Thank you both, Ray and Terry.

I'm currently looking for digital pH-meters. What I have learned so far is that the probes last about a year with regular use and then need to be replaced. With irregular use and good care, up to 2 years. But they cost almost as much as a new device.

Furthermore the pH-meter probes can usually be used for water >200 µS/cm. There are special pH-meter probes that can be used with water >20 µS/cm. From this I draw the conclusion that when measuring with RO water the standard probes show deviations - although the question here is how big this is - because there are only very few ions in the water.

Then what about pH test sticks? The topic of pH measurement does not seem to be as simple as measuring conductivity.

 

[terryros]

Istvan, I have used Apera pH and EC meters. I think they sell in Europe. The pH meter uses a single calibrator solution at pH 7.0. Since I am only trying to be sure that my fertilizer solution is around 5.8, I am content with a single calibrator. The EC meter uses a single calibrator (I think 1413) so my fertilizer solutions in the 500-700 range are easily measured and don’t need to be exact. Both meters are compact and easy to use.

I think like you, I need my water mixture to be RO with 15-20% tap water to achieve the pH target.

 

[katzenhai2]

The tried and true "pour-through" test is pretty reliable:

• Water the plant thoroughly, drenching the potting medium with the solution of your choice.
• Wait 60 minutes for the pot to fully drain and for the “pot chemistry” to come to equilibrium.
• Trickle enough pure water (distilled is best) evenly over the surface of the medium to collect about 50 ml (a shot glass) of the drainage.
• Test the pH of the collected liquid. That is representative of what the plant experiences.

The drainage water has only 90 µS (with 30µS of my RO water). Unfortunately the pH value cannot be determined reliably with standard pH electrodes when using RO water.

 

[Arne]

The drainage water has only 90 µS (with 30µS of my RO water). Unfortunately the pH value cannot be determined reliably with standard pH electrodes when using RO water.

You will get an instantaneous value for the pH which will serve its purpose. It will not mean anything if you measure over time though because the pH will drift. The lower concentration of salts, the faster the drift of pH.

 

[katzenhai2]

You will get an instantaneous value for the pH which will serve its purpose. It will not mean anything if you measure over time though because the pH will drift. The lower concentration of salts, the faster the drift of pH.

From everything I've read about pH electrodes the problem is as follows:

Due to the low salt content in the water there is increased resistance between the two electrode measuring points. Therefore the measured pH value is too high than it actually is. The range is between 0.3 and up to 1 pH value which I find to be relatively high with large fluctuations depending on the salinity of the water.

For water with very low conductivity there are special (expensive) pH electrodes that release some potassium chloride into the water around the electrode to reduce resistance. A simple measurement with standard electrodes leads to incorrect results.

I had already thought about adding a few drops of potassium chloride to the water to balance it out as this salt is supposed to be pH neutral. Since I'm new to pH measurement I'm not sure if the measured values are reliable.

 

[terryros]

The drainage water has only 90 µS (with 30µS of my RO water). Unfortunately the pH value cannot be determined reliably with standard pH electrodes when using RO water.

You must be using a very low concentration of fertilizer. With a fertilizer solution that is approximately 100 ppm N and an EC that is in the 600-700 µS range, I get a pour-through EC of about 200 using RO water with an EC of 5. With a 200 µS solution I think the pH will be valid.

 

[katzenhai2]

You must be using a very low concentration of fertilizer. With a fertilizer solution that is approximately 100 ppm N and an EC that is in the 600-700 µS range, I get a pour-through EC of about 200 using RO water with an EC of 5. With a 200 µS solution I think the pH will be valid.

I think I know where the mistake is: I only used RO water when watering. I should have followed Ray's advice to the letter (using a fertilizer when drenching the pot).

I usually use around 500-600 µS. For a day in between I just flush with RO.

 

[terryros]

I think I know where the mistake is: I only used RO water when watering. I should have followed Ray's advice to the letter (using a fertilizer when drenching the pot).

I usually use around 500-600 µS. For a day in between I just flush with RO.

I think what you did still shows that you are not accumulating salts in your potting media.

 

[katzenhai2]

Watered today with 600 µS (only calcium nitrate). Waited 2 hours after watering, then used RO water and collected about 50-100ml at the bottom. EC of my RO water: 30 µS. EC from collected water: 90 µS.

What am I doing wrong? Waited too long?

Btw my paphs are all constantly wet, if that's important. The pots stand between sphagnum moss. Does this possibly exchange nutrients with the pot substrate? There is no direct contact but puddles of water at the end of the pot could maybe... would have to investigate more closely.


Top view of the empty spaces where the pots stand. Does the moss then feed on the fertilizer? No wonder it grows so lushly...

 

[terryros]

What does watering mean for you? Is it a large volume of solution or only a modest amount? You are adding it to the pots in place in the moss, so I am thinking the amount isn’t very large?

 

[katzenhai2]

What does watering mean for you? Is it a large volume of solution or only a modest amount? You are adding it to the pots in place in the moss, so I am thinking the amount isn’t very large?

I take out the pots and use a sprayer over a bowl to spray about 500ml onto the substrate per pot. I never thought about it but this way each plant only receives half of the fertilizer...