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pH Drift
Alkalinity vs…. alkalinity

When it comes to pH, there is a few different terms used to describe if the pH is low (<7) or high (>7).  If you want a refresher on what pH is and why we should care, check out our pH post

Substances with a low pH are called acids, and high are called bases.  However, some say alkalinity instead of base.  This can cause a great deal of confusion when describing the concentration ( [x] ) of naturally occurring Calcium Carbonate ([CaCO3]) in water, as this is also typically referred to as Alkalinity.  Another way you may have heard the measurement of this concentration described is “hardness” and instead of CaCO3, you might have heard lime.  It is important to understand the differences between alkalinity as pH and alkalinity as [CaCO3], and we will get into why below.

While [CaCO3] does not directly infer a certain pH, it does impact it.  The higher this concentration, the greater buffering or resistance to change in the pH the solution will have.  If you are trying to lower or raise the pH, the more CaCO3, the more acid or base you will have to add to get to your desired pH.  The Ca++ ion is positively charged, and the CO3 ion is negatively charged. Note that they are double charged, so each ion can form two bonds.

This double bond is what makes them a good buffer, as they are each able to bond with two ions of singular charges when they disassociate.   There are some spectrum analysis tools available for [CaCO3] testing but are currently all manual and require consumable reagents.  Your source water usually will not vary much, so if you have a water quality report from your local municipality or from a well test on hand, you should have a good idea of the water’s [CaCO3].

So next time you are analyzing your fertigation water, know that when you’re trying to change the pH, you will have to contend with the amount of [CaCO3] that’s already in the water, and because not all starting water is the same, the same fertilizer recipe with different water may require vastly different amounts of acid/base to get your fertilizer water into an appropriate range.  There will be more blogs on the topic to come.  If you have any questions or comments, feel free to reach out to info@phenologic.com

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