# EC-meter (DIY)



## BluesBoy (Jul 2, 2004)

Hi!

I have built an own pH-controller with data logging of pH x 2, water temperature, status of the CO2-solenoid, CO-consumption etc:
http://www.bluesboy.se/viewimage.php?id=355

The latest feature I'm trying to add to this controller is an electronic conductivity meter (EC). I have built an electrode prototype with two carbon electrodes in a plastic housing. 
http://www.bluesboy.se/viewimage.php?id=407

I have built up the circuit based on a PWM signal from the microcontroller with some AC-coupled capacitors so the signal to the electrodes is an alternating current (100 Hz) proportional to the resistance in the water. 
Well, it seams to work quite well if I measure and compare tap water, tank water before adding nutrients and after adding nutrients. http://www.bluesboy.se/viewimage.php?id=426
http://www.bluesboy.se/viewimage.php?id=416

If I do a 50% water change the signal is decreasing as expected.

Now my problem:
I cannot see a decreasing signal when the plants are running with good photosynthesis (heavy pearling) for a week or two without adding more nutrients:
http://www.bluesboy.se/viewimage.php?id=421

The plants are running at high speed so I assume there should be a great nutrients uptake even if I only have 0,3 W/l light. This movie sample shows the photosynthesis after 12 days without adding more nutrients:
http://www.bluesboy.se/movies/Kondukt12.wmv (Windows Media 4.3 Mb) and this is an overview of my 540-litres tank: 
http://www.bluesboy.se/viewimage.php?id=418

Does anyone have any ideas why the (measured) EC is constant for so long time? Anyone who have measured TDS or EC with good result (expected nutrient consumption)?

Thanks in advance!


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## plantbrain (Jan 23, 2004)

Bacteria will maintain it, some inorganics will exchange some and keep it relatively stable, and the plants also have some influences on the EC.

Plant uptake often involves counter ions they use. The nutrients are incorprated into their tissue whilwe the counter ions are pumped into the water column. So the EC generally will stay the same unless things are limited/unbalanced etc.

Also, make sure you give enough time for the EC to stabilize.
You might try redox and mV also.


Regards,
Tom Barr


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## plantbrain (Jan 23, 2004)

You can make a Redox probe fairly easily if you have a ISE or a mV type meter.
A sodering iron, solder, some 18 gauge wite, 1 cm of platinum wire, I think 18 gauge as well and plastic tube.

Solder the tip of Pt onto the wire. Silicone the ends.

Hook wire up to a BNC.
If you have a calomel ref probe type mV meter, that is best.

You can make the redox probes as long as you wish.
So 2ft probes placed into you substrate as a function of time can be done.
If you place several in your tank upon start up, you'll get a good idea of the nature of the substrate during the start up phase.

You can put quick release attachments onto each probe, so you can swap probe readings with one mV meter.

The connections need to be out of water, but the probes can be made any length deisred and you can also measure the Redox depth difference through time as well.

Or as a function of depth in single location. Simply push the probe downward in 25mm distances for each movement, wait 1-2 hours then take the reading.

You can also try at different distances from the roots of the plants also compared to areas without plant roots.

Lots of different things few folks in the hobby have ever tried.

Keep it up.

Tom Barr

www.BarrReport.com


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## BluesBoy (Jul 2, 2004)

plantbrain said:


> Bacteria will maintain it, some inorganics will exchange some and keep it relatively stable, and the plants also have some influences on the EC.
> 
> Plant uptake often involves counter ions they use. The nutrients are incorprated into their tissue whilwe the counter ions are pumped into the water column. So the EC generally will stay the same unless things are limited/unbalanced etc.


 That explains the behaviour I got=D> . I thought EC could be used to see when it is time to add more nutrients due to plant uptake (consumption). If I now understand the theory correct I can use it to see when it builds up too high levels (time for wc) due to small errors in dosing regime/uptake rate? 
In that case the next step for me is to add nutrients one by one and see the influence of EC - just to get a better understanding. I know the EC is the sum, but it would be interesting to see the effect of individual nutrients.

Edit: You was too fast  A new post before I answered. 
I will consider your suggestion about the redox probe. Thank's!


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## plantbrain (Jan 23, 2004)

BluesBoy said:


> That explains the behaviour I got=D> . I thought EC could be used to see when it is time to add more nutrients due to plant uptake (consumption). If I now understand the theory correct I can use it to see when it builds up too high levels (time for wc) due to small errors in dosing regime/uptake rate?
> In that case the next step for me is to add nutrients one by one and see the influence of EC - just to get a better understanding. I know the EC is the sum, but it would be interesting to see the effect of individual nutrients.
> 
> Edit: You was too fast  A new post before I answered.
> I will consider your suggestion about the redox probe. Thank's!


Sorry to ninja post

Well EC is a pretty generalized thing, not a bad idea to play with, but practical matters are another issue. If things get out of whack, then you can have some movement, but if things are running smoothly, the EC will not help you, the other issue is source water EC can change......

It is a good idea to do the individual nutrients in a test, then you can get a good feel for which are significant in terms of EC.
I have not done that.

Just the general.
But most lost interest in it.

regards, 
Tom Barr


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