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Monitor Your Monitor: How Your pH Meter Actually Works In Your Grow Room

Make sure your pH monitor is working well or it could cost you! Make sure your pH monitor is working well or it could cost you!


Ever want to know what exactly is happening when you test the pH levels in your hydroponic garden? It’s not as complicated as you might think. This new column will seek to explain the science that happens inside your grow room. Ready for a master class?

For starters, we all know that water is H2O‚ but a chemist will write it HOH because when you view water as H(ydrogen) and O(xygen), pH makes a lot more sense. More H’s mean more acidic, and more O’s mean more alkaline. When H and O are balanced you get pH 7.0 — pure water. pH actually stands for power of hydrogen concentration, an exponential logarithm that means that pH 5 is 10 times more acidic than pH 6. Now that you know this basic chemistry, you’re ready to start understanding how a pH probe works.

No matter how fancy a pH meter is, at its core is a silver electrode in a silver chloride solution. This makes a battery that is sensitive to changes in H-ion concentration on the other side of some very delicate glass. When submerged in pure water, the battery generates 0 volts. But if the water is acidic or alkaline, it creates a positive or negative charge depending on whether the pH is above or below 7. At 25°C, you get about .059 volts for each point of pH.

Glass electrodes are delicate, and soluble ions in the probe will actually migrate through the glass during extended exposure. For that reason, caring for your pH probes is essential for getting accurate readings. There seems to be a lot of confusion in the growing community on the care of pH probes, so here’s the actual science:

- Always store pH probes in acidic solutions. PH 4.0 solution is fine, and tap water will do.

- Never store probes in R.O. or de-ionized water. Ions will migrate into the water, killing the probe.

- Never let probes dry out. The glass will develop micro-cracks, making it read erratically.

- Keep probes out of bright light. The silver compounds in the probe are photosensitive.

- Clean your probe by swirling it in pH Down, then R.O. water, then pH Up, then R.O. water. Repeat a few times until the probe is clean.

I have probes that are 10 years old and work perfectly. I wouldn’t bet a grow cycle on them, though! The only way you’ll know your probe is failing is if you get dead plants. Replacing pH probes once a year is cheap insurance.

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pH Perfect from Advanced Nutrients takes care of your pH problems.
Last modified on Wednesday, 23 January 2013 18:33

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