Measuring your 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, pH test strips are just 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!

Maximum nutrients are available at a pH of 6.2 to 6.5

On the other hand, many old-time soil gardeners swear by 7.0 as the pH you want to keep. This is mainly to benefit the 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 (even without humic acids present). I only say all of this to prove a point- pH test strips and pH drop indicator tests are both 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 just as accurate as the day I bought it, and I have never purchased any calibration solution.

Get Accurate pH Readings

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.

You should never need to buy calibration solution really. 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 cup of room temperature tap water to be sure. Better yet, use distilled water!

Having done it both ways myself, I really have no preference. PH test strips and drop kits 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 or drop kits....it is very convenient to leave a bottle at each location, just in case you forget your pH meter (or your batteries die).

Adjusting your Nutrient Solution pH

Check the pH of your nutrient solution at least once every day. From time to time you will need to adjust the pH. This should only be done with high quality pH UP and pH DOWN products specifically made for hydroponic gardening. Add them a little at a time, mix the nutrient solution well, and retest the pH until it is OK. When maintaining your nutrient solution, always check and adjust the pH first. Check and adjust the nutrient solution strength last, because the addition any pH UP or pH DOWN will increase your nutrient solution strength.

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