Over the past few weeks, the most common email questions I’ve been receiving have been related to pH and TA – and understanding their relationship. They really are very close “cousins” and the relationship is pretty interesting.
Today, we’re going to discuss EXACTLY how the relationship works so you have a better understanding.
IMPORTANT: I also have a MAJOR announcement for SPA owners that I’ll get to at the bottom of this message.
Let’s dig deeper for a better understanding…
However, the relation ship between pH and total alkalinity (TA) is the most instrumental one that resides in your body of water…
If the total alkalinity is in the right range, pH won’t be so volatile. If your pH is bouncing, chances are the TA is too low. TA is the real driving force to controlling the pH.
If a service tech or do it “yourselfer” doesn’t understand this relationship, poor water balance can result.
TA is the governor of pH. Don’t try to change the pH unless the TA is in the right range. The first correction is always TA…then you address any pH issue. And you may never have to change it if the TA is OK.
Here’s a look at exactly what pH and TA are, how they relate and interact and what service techs can do to keep it all under control.
What is pH?
Let’s go back to High School chemistry class (I’ll keep it painless and I promise there’s no test at the end).
pH is defined as a measure of water’s acidity or alkalinity. This is done by determining the power of hydrogen ions (H+) in the water. These ions are measured on a logarithmic scale from 0-14, with 0 being the most acidic and 14 the most basic or alkaline.
In simplified terms, pH is actually counting how many hydrogen ions are in the water.
Ideally, one is shooting for 7.4 to 7.6, slightly on the base side of neutral. This is a comfortable range for humans as well as the optimal pH range for chlorine to do its job.
Keep in mind that extraneous factors from both people and Mother Nature can alter pH levels. Things such as pool parties with high bather loads or heavy rainstorms, especially when the rain tends to be on the acidic side, all have an impact. In the wake of such events, we need to check water chemistry variables as soon as possible.
If the pH is allowed to dip below the 7.2 minimum standard, the water becomes more acidic or, as it is sometimes known, aggressive. This can lead to equipment corrosion, pool surface damage and inefficient sanitizer use.
If the pH rises above the 8.3 level, the pool may experience scale and high turbidity. In either case, skin and eye irritation can be an end result here.
It is important to monitor pH levels because the number drastically impacts the Saturation Index equation – a formula used to diagnose water’s chemical balance.
When the pH changes (for any reason),so does the Saturation Index.
That’s because although both TA and pH figure into the Saturation index, pH has a larger impact on it.
For example, a TA reading of 150 ppm uses a factor of 2.2 in the formula. A reading of 200 ppm is represented by a factor of 2.3. In fact, TA ranges from100 to 300 ppm are represented by factors ranging only from 2.0 to 2.5.Consequently, it takes a major shift in TA ppm to affect the results of the Saturation Index formula.
On the other hand, the Saturation Index uses the actual pH reading in the formula – not a factor–so the change in the pH will have a profound effect on the outcome.
Whatever the pH changes, the index will change in the exact same amount. It’s a 1:1 factor. If you want to change the Saturation Index, lower or raise the pH.
When pH levels stray, most employ muriatic acid to lower it and sodium bicarbonate or soda ash to raise it.
However, it’s not always that simple. If all the variables are not in their proper ranges as well, particularly total alkalinity, it can be difficult keeping the pH within ideal limits.
The TA/pH relationship:
Total alkalinity has an important relationship with pH in swimming pool water. But first, what exactly is TA?
Total alkalinity is essentially a natural buffering system that helps to stabilize pH readings. If pH is counting how many hydrogen ions in the water, TA is counting how many things in the water are capable of absorbing hydrogen.
Simply put, total alkalinity is made up of things that can take on hydrogen.
At higher pH ranges, total alkalinity is the combined presence of hydroxide ions (OH-),carbonate ions (CO3) and bicarbonate ions (HCO3).
However, in swimming pools and hot tubs, where the pH range shouldn’t stray too far from the recommended mid 7 range, TA remains strictly a bicarbonate.
TA is nearly 100 percent bicarbonate in pools unless the pH is in the 9.0range or better. You can define TA as the sum of alkaline salts and, in essence, to simplify things…the primary one is bicarbonate.
When TA levels are too high or too low, it affects overall water balance. For example, with water that has very low TA levels, the pH is under stabilized and will change dramatically whenever even small additions of chemical are made.
Water becomes more corrosive to plaster and metal fittings and heater elements. In conditions of excessive bicarbonate alkalinity, the pH is overstabilized and tends to remain around 8.3. The pH level is likely to bounce back to the 8.3 range even after acid is added. With TA and pH in such high ranges, dull, turbid water also can result.
I truly hope this pH and TA “overview” helps manage this interesting relationship – it can be a complicated one. I’ve really tried to break it down to something that isn’t terribly technical so it can be better understood.
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All the best,
Terry Duff
{ 4 comments… read them below or add one }
This has been the best information I have ever received concerning ph and ta in swimming pools. It gives me a better understanding of how they relate and what is going on in my pool. I have had a problem for sometime controlling the ph because my ta was always low(74-78). I thought by raising the ta to the recommended level it would raise my ph significantly. Thank you for this informative article.
Hi Gary,
Music to my ears – truly glad the info helped you. As a sidenote…one item not addressed in there that I should have mentioned.
Generally speaking, dial the TA in first…a likely result may be low pH – if it’s still above 7.0, wouldn’t take action as it should naturally rise in coming days.
If it’s below that…would recommend using sodium bicarbonate to life pH levels. This will have a minimal impact on the TA number.
Thanks again Gary.
Terry
Terry,
I must echo Gary’s sentiments.
You’ve dropped the bomb on this explanation.
Plus, thanks for taking me back to High School Chemistry. I didn’t do all that well back then, but you pulled me through your explanation with flying colors.
Thanks.
Many thanks Bill!
Appreciate the kind words…can be a fairly boring topic – glad it made sense.