Before learning about calibration solutions, it is important to learn about the pH pen you are trying to calibrate and how to take care of a pH probe properly.

Now, we learn that when you press “calibrate” on a ph pen, as part of its software, it will reset to 7.0 no matter what the actual pH of a solution is. This is why you calibrate it using the 7.0 calibration solution so that when it resets to 7.0 it is actually in a 7.0 solution. This starts us off on an even field and allows us to correctly move forward. 

But, since we now know that we are forcing our pen to say 7.0, how do you know if the probe is reading accurately 7.0 or if it’s only reading 7.0 because you reset the pen? That’s when the 4.0 calibration solution and the 10.0 calibration solution come into play.

You need to check both sides of the spectrums on the scale, the acid side and the alkaline side.

When you dip the newly 7.0 calibrated pH pen into the 4.0 solution it should read 4.0 or very close to it. Respectively, when you place the probe in the 10.0 solution it should read 10.0 or very close to it.

However, if you calibrate the pen at 7.0 and then you place it into the 4.0 calibration solution and it reads something completely different like 5.6 or you place it into the 10.0 calibration solution and it gives you a number nowhere close to 10.0 either then something is wrong with the pen.

Sometimes one side of the pH scale might be off but the other side is being read accurately.

Let’s say you expose the probe to sunlight and now it reacts stronger to the acid, so now when you calibrate it and then place it in the 4.0 calibration solution the reading might be way off but when you place it into the 10.0 calibration solution it reads it just fine. so now you know that the pen is not reading the acid side of the pH scale correctly. Which, can lead to problems if you are trying to measure something that has a low pH. And vice versa.

If your pen reads the 4.0 calibration solution correctly then it will most likely read the acid side of the scale (between 1and 6.9) correctly. And if it reads the 10.0 calibration solution correctly then it will likely read the alkaline side of the scale correctly (7.1 to 14). Once your pen starts reading these solutions incorrectly, however, then there will start to be a misreading on whatever side is giving you issues.

What do you do if your pH pen is giving you incorrect readings?

At this point, once you’ve determined that your pH pen is having problems reading either, or both, sides of the pH scale, the only solutions are to buy a new pen or, if you have a pen with an interchangeable probe, replace the probe.

Most people don’t feel like they need to purchase all 3 calibration solutions and just get the 7.0 to reset their pH pen, but, as you’ve learned here, that doesn’t work. Once you understand why you need all three then it becomes clear.

For the most part, all pH pens last about 6 months, and even though companies say they come calibrated, between travel and storage they become uncalibrated, so these calibration solutions are vital to making sure you know what the pH of your solutions are. 

Remember, having the correct pH is imperative to the well being of any plant you cultivate.

Is there a way of going around buying all the calibration solutions if you really don’t want to buy them?

The only quick fix answer for not wanting to buy all the solutions but still checking to see if your pH pen is working correctly is buying pH strips or a pH test indicator. These are very inexpensive and can be used as a reference for your pen.

Before adding any nutrients to your water use the strip/indicator to check the pH of the water, this will give you a rough estimate of the pH, then use your pen to measure the same water, if it correlates with the strip/indicator then your pen is likely working correctly.

PH strips and test indicators, however, do not work after nutrients are added to the water because most nutrients are dyed and do not allow the strips/indicators to function properly making them obsolete. 

If your pen does not agree with the strip/indicator when measuring the pH of the water then you will have to end up buying the calibration solutions in order to calibrate or determine what the issue is.