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I was blessed to get some great questions as a result of the post I made about my latest hydro lettuce station.  I am learning as I try things out and through getting great questions and feedback like the one from gotbock.

gotbock’s question::

post replyMy Hydro setup

 

 

from gotbock via /r/hydro/ sent 5 hours ago

Do you know if you’re pH and EC probes are designed to be held in your nutrient solution for long time periods? Most meters I’ve used require at least the pH probe to be stored under storage solution (usually saturated KCl) when not in use to maintain the probe. Otherwise they will go out of calibration pretty fast.

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After researching, I came across this article which helped me better understand the why of gotbock’s point and what I would do differently given the probe stays in a nutrient solution.

ionsonglassmembranepH

The article notes that if the glass membrane is kept in a solution that has plenty of sodium and potassium ions (which a nutrient solution would), these ions will penetrate the membrane along with the hydrogen ions. Now instead of measuring H+, the probe provides measurements of Na+ and K+…so the pH readings are off as you point out. The ions that are a key part of the nutrients will adhere to the glass and off go the readings.

As gotbock notes, the best way to prevent this is to clean off the glass membrane with distilled water and then store in a storage solution.

I have not done enough testing to understand the practical challenge (how inaccurate) the readings will be. Especially since I am monitoring for a range of readings. For example, I’m growing lettuce so I want the pH value to be between 5.5 and 6.5.

I would agree calibration would have to be done more often. I don’t know how much more often. Once I automate this process with the Ladybug Shield, I can choose to calibrate daily/weekly, etc. with the goal of minimizing this challenge.

 

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