TDS probe questions

Hi all, i've done a couple of hydro grows before and am doing one again (after many years!), i bought a cheap TDS probe (https://www.amazon.co.uk/HoneForest-Accurate-Temperature-0-9990ppm-Aquariums/dp/B073713G5F/ref=sr_1_19?dchild=1&keywords=tds+probe&qid=1605653126&quartzVehicle=36-1774&replacementKeywords=tds&sr=8-19)

This time around i want constant monitoring of EC/PH/Temp so i bought a TDS probe to use with an Arduino uno.

The cheap probe says the water is at around 0.9 EC, the Arduino probe says it's around 0.47. If there was a small difference i wouldn't worry but this is a large difference.

How accurate are the cheap probes and has anyone else used an Arduino probe like this one : https://www.amazon.co.uk/Xineker-Conductivity-Arduino-Detection-Quality/dp/B07T73P185/ref=sr_1_2?dchild=1&keywords=arduino+tds+probe&qid=1605653289&quartzVehicle=36-1774&replacementKeywords=arduino+tds&sr=8-2


Cheers.

Did you calibrate both probes?

Thanks 930G. The manufacturer says the Arduino probe needs no calibration, it also does temperature compensation. The cheap meter has no calibration screw. I think i'll buy some calibration fluid and check them.

plantastic said:

I think i'll buy some calibration fluid and check them.

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yep

rkymtnman said:

yep

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Delivery will take too long, found this though : https://scienceinhydroponics.com/2017/03/how-to-prepare-your-own-solutions-for-ec-meter-calibration.html

plantastic said:

Delivery will take too long, found this though : https://scienceinhydroponics.com/2017/03/how-to-prepare-your-own-solutions-for-ec-meter-calibration.html

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get some distilled or RO water and see what it reads. dasani is RO (pretty sure?). should read really close to 0 EC

rkymtnman said:

get some distilled or RO water and see what it reads. dasani is RO (pretty sure?). should read really close to 0 EC

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Thanks rkymtnman, i distilled some at home and the ppm was ~125 so an EC of 0.25. Trouble is that that's the same reading after i add canna aqua a+b and some calmag.

Waiting for the proper fluid to arrive.

I'm cheap as fuck so I did this:

And had reliable numbers on my arduino, so I would say the manufacture is full of crap and that their sensor should be calibrated, or at the very least whatever it's default values for known reference standards should be stored in vars to translate into the correct values.

Thanks guitarguy