Measuring the Nutrient Solution pH

by Michael E. Basham
(Virginia)

My question is about nutrient solution pH levels. I started my first hydroponic garden about six months ago. and I have had a moderate amount of success. One thing that I have yet to get settled in my mind is what method to use in measuring the pH levels in my various systems. Some sources say it is better to use test strips, while others say a moderately priced meter is the way to go. One con in regards to using a meter is the calibration solutions that must be used to keep it accurate. What method would you recommend for a home hobbyist?

Answer: Michael- for the home hobbyist, test strips should be fine for monitoring the nutrient solution pH. There are a number of reasons for this. First, the ideal range for the pH is around 6.2....this is the spot where the maximum number of primary, secondary, and micro-nutrients are available. However, when hydroponic gardening, many growers use a much lower pH. I personally have known growers who mix their nutrient solution up at 5.2-5.5 pH, and then let the pH of the solution slowly drift upwards over time. Be careful if you try to do this....some plants will not tolerate it!

On the other hand, many old-time soil gardeners swear by 7.0 as the pH you want to keep. This is mainly to the benefit of beneficial micro-organisms in the soil, which in turn release humic acids, which in turn help to keep nutrients chemically available at a pH of 7.0. However, even in a hydroponic system, the vast majority of the nutrients are still available at a pH of 7.0. I only say all of this to prove a point- pH test strips are more than accurate enough to manage your nutrient solution pH effectively.

On the other hand, a good pH meter is more accurate. Even though it is expensive when you first purchase it, you never have to worry about buying pH test strips ever again. I owned a Milwaukee pH meter for the last 10 years....it is still as accurate as the day I bought it, and I have never purchased any calibration solution.

The first thing you want to do to keep your meter accurate is to always keep it clean! Every time you test your nutrient solution pH, you should immediately rinse the probe with plain water. I used to keep a little calibration solution in the rubber cap of the probe, but this is not absolutely necessary. The second thing is DON'T ever touch the glass or metal parts of the probe with your bare hands (or anything else, really)....the oils from your hands will affect the pH reading, and so will any scuffs or scratches on the glass part of the probe.

Finally, you should never need to buy calibration solution. I did so a couple of times when I first got my pH meter, and it is a waste of money. Instead, I made sure the instrument was accurate when I first purchased it (they usually come with one packet of calibration solution), then I tested some room temperature tap water. Municipal water supplies are usually very consistent as far as pH is concerned. Simply remember what the pH of your tap water is supposed to be, and from time to time test the meter in a little room temperature tap water to be sure.

Having done it both ways myself, I really have no preference. PH test strips are certainly more affordable. If you have multiple locations that need the nutrient solution pH tested, this is another reason to go with test strips....it is very convenient to leave a bottle at each location, just in case you forget your pH meter (or your batteries die). I hope this helps you out Michael, and Happy Growing!

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