What pH is Best for Pools?

Experienced service techs know that the pH in many of their pools generally rises above 7.8 within four to seven days following chemical treatments.  It is a chemistry reality that when water contains 80 ppm to 120 ppm of carbonate alkalinity, and is left alone and untreated by additional chemicals, the pH will rise to 8.0, and sometimes as high as 8.4 and stay there until chemically treated again. 

What does this mean?  It means that thousands upon thousands of residential pools are not kept within the (APSP-recommended) pH range of 7.2 to 7.8 on a constant basis. This has been true ever since pools starting getting built in residential backyards many years ago.  Yet, there is no indication that unsafe conditions or other problems have resulted from that fact. 

However, for the past 50 years our industry’s chemists, class instructors, and trade associations have been advocating to service techs that a pH above 7.8 is wrong, unsafe, automatically unbalanced, and causes various problems. Is that true, or not?

How Standards Got Started 

Let’s consider what happened 50 to 60 years ago that probably influenced our industry to adopt the restrictive pH range of 7.2 to 7.8 as our standard.

At that time, calcium hypochlorite (Cal-hypo) and sodium hypochlorite (bleach) were the primary sanitizers for residential pools.  It was observed that adding Cal hypo or bleach to pool water with a pH of 8.0 to 8.2 would sometimes cause cloudiness.  It was also observed that maintaining a pH of 7.2 to 7.8 and a lower alkalinity helped reduce cloudiness when those sanitizers were added.

So it makes sense that some in our industry promoted the concept of keeping the pH at a lower range of 7.2 to 7.8 and the alkalinity below 180 ppm to avoid making pool water cloudy. 

However, for some reason, what started out as a reasonable standard for bleach and Cal-hypo pools a half-century ago got out-of-hand, and our pool industry has ever since been (incorrectly) taught that a pH above 7.8 automatically causes cloudy water and scaling conditions, causes eye and skin irritation, and that pool water at higher pH levels cannot not be properly sanitized with chlorine no matter what.  And those same false claims were also applied to alkalinity levels above 180 ppm.

In all fairness, those recommended levels may be a good standard when using those alkaline sanitizers and in hot weather areas – but not necessarily for all other pool products and other pool conditions.

The fact is that the pH of pool water can be easily maintained at 8.0 to 8.4 without either cloudiness or scale. At the time the standard was introduced the Saturation Index was not commonly used in the industry, but now it is regularly used and understood.  Simply maintaining the water within a balanced LSI range is all that is required to avoid cloudiness or deposits from calcium precipitation.

Also, there are studies that show that eye irritation does not develop until the pH rises above 9.0 or is below 7.0. This is consistent with the EPA drinking water standard, with high pH eye drops for soothing irritated eyes, and in fact higher pH levels even lead to less irritation from chloramines when they are present.  Yet current APSP literature still contains the listing of incorrect consequences of high pH and alkalinity.

With the availability of other chemicals and new technologies, including acidic or near-neutral chlorine sanitizers such as Trichlor and Dichlor, our current industry’s chemists, associations, and those who are writing our standards should consider modernizing the chemistry parameters for all pool situations and conditions.


How to Achieve Good Chlorine Efficacy

In addition to water balance, let’s examine the most important aspect of pool water treatment, which is keeping pool water properly sanitized and safe for swimmers.  This topic has also been misunderstood. 

Again, for fifty years, many seminar instructors have stated something like “high pH makes chlorine less effective, or at high pH, chlorine is not powerful enough to get the job done.”

Many who hear that incomplete statement end up believing that no matter what, high pH prevents effective sanitizing by chlorine, and that there is nothing that can be done to overcome this “fact.”  But that would be the wrong conclusion. 

The following question should be asked: is it possible to achieve sufficient and effective sanitation with a pH above 7.8?  The answer is yes.  All one has to do is to increase the chlorine level slightly higher to achieve the same amount of chlorine efficacy and effectiveness. How easy is that?

For example, let’s start with pool water that has a pH of 7.8, and contains 1.0 ppm of chlorine, which is an “acceptable” amount of chlorine efficacy according to industry standards.

If the pH of pool water is 8.2 (which often happens in many pools), all that is needed to achieve the same chlorine efficacy is to increase the chlorine level to 2 ppm.  That’s it; just add an extra 1ppm of chlorine.  That would match the chlorine efficacy of 1.0 ppm at pH 7.8. 

This means that there is the same amount of hypochlorous acid (HOCl) at a pH of 8.2 with 2 ppm of total chlorine as there is at pH of 7.8 with 1 ppm of total chlorine.  And of course, maintaining the chlorine residual above 2 ppm provides a greater amount of chlorine efficacy, including more in reserve for long-term sanitizing.

Let’s also understand that as the more active chlorine (hypochlorous acid) gets used up by killing bacteria and algae, the less-powerful hypochlorite ion will start converting over to hypochlorous acid very quickly, and therefore, soon becomes the more powerful type (hypochlorous acid).  The hypochlorite ion does not remain as hypochlorite forever, which is sometimes misunderstood. 

Interestingly, sanitizers such as ozone, UV, and PHMB (biguanide) are not affected by a high or low pH.  Bromine efficacy is still considered effective at a pH of 8.4.  So why is there a restrictive pH range of 7.2 to 7.8 for those products?

So can there be adequate sanitizing efficacy and a good margin of safety when maintaining a pH of 8.2 or even 8.4?  Absolutely.  The science shows that and so does empirical evidence.  So why limit the available options of providing properly sanitized swimming pool water for our consumers?


Flexibility is Needed

While we are on the subject of allowing higher pH levels for swimming pools, it is interesting to note that there are water municipalities that provide tap water with a pH in the range of 8.8 to 9.3 to millions of residents.  Yes, that is correct, and they add about 2.0 ppm of chloramines for sanitizing. That water is safe, and does not adversely affect people who ingest or bathe in it.

Even the PhD chemists at Olin Chemicals 40 years ago wrote that a pH of 7.2 to 8.4 was non-irritating to the eyes, and was more of a concern when the pH is below 7.2.

Another point is that many service techs (and even self-maintenance pool owners) have been following the Jock Hamilton Index, which recommends maintaining the pH at 7.8 to 8.2, and they have been successful at doing this for many years without problems.

Since the pH of pool water generally wants to rise to 8.0 and often up to 8.4 (assuming a moderate alkalinity), and since that pool water can be properly balanced and sanitized, without eye or skin irritation, and without cloudiness, why not allow service techs to maintain pool water at a pH of 8.0, 8.2, or even 8.4 when they are using a non-alkaline sanitizer?

Why are restrictive standards being imposed that may make maintaining pool water more difficult, cumbersome, and complicated in certain conditions?  There can be easier and more effective ways to maintain pools, and not only is that possible, it is the way many experienced service techs and pool companies are maintaining their pools today, and have been for over 40 years.

This is not the first time that service technicians have pointed out that chemical experts could use a little advice or even correction. Service professionals demonstrated that the “Acid Column” technique was a myth, and it was service professionals who corrected the industry’s dosage charts for acid and baking soda.

Currently, the APSP is developing a new water chemistry standard for residential pools.  Now is the time to modernize and correct the old material that is in need of an update. Service technicians have much to contribute to the process, rather than relying on old and occasionally incorrect information. Now is the time to create standards that can withstand scientific and reasonable scrutiny – and allow for us to work smarter rather than merely “the way it has always been done…”

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  • Hi Kim if you are around?

    I had to recently use some eye drops, remembering your post about them being a high pH. They did make my eyes water but I wondered if the high pH actually caused a auto response from the tear ducts to a high pH solution? It felt much better when the tears did their job more than the drops.

  • Hi John,

    Excellent points. You are correct that Vinyl or Fiberglass pools can be maintained properly using different parameters than what the industry suggest is Ideal. 

    I will be posting another article about the industry's recommend "Ideal Alkalinity" range and will be addressing some of the points that you have mentioned.

    It is true that once hypochlorous acid is used up sanitizing the water, that the hypochlorite ions will convert over to hypochlorous acid very rapidly to continue the sanitizing process, and that happens regardless of what the pH is.

  • Interesting post Kim, I think the issues which get overlooked are the information for different types of pool rather than  lumping them all in together as "Pools" from your excellent posts on plater etc to vinyl pools each type can have its own chemistry. My vinyl lined pool is my test bed and I run with Alk low at around 35-40ppm which easily provides a rock solid pH of 7.4 despite many adults and my bubbling air through the water to try and increase the pH. Bicarbonate of soda in water produces a pH of around 8.4, too high really so a lower buffer like borates, cyanuric acid or magnesium chloride could well be useful to prevent the pH drift upwards.

    I get that we can increase the chlorine level to offset the high pH and that may well be what has to happen in plaster pools to protect the surface but again in others that would give rise to using more chlorine to arrive at the same sanitation active level but in the times of trying to reduce chlorine levels this feels like going backawards.

    I did not know that the chlorine would convert from the ion side to the acid side without a reduction in pH as I was led to believe that was the/mechanism that controlled that, is that not the case?

    I seriously believe that in order to progress we do indeed need to dump the old ways but the new way shouldnt be with extra chlorine it should be through better filtration.  Finer filtration removes more of the organics that chlorine reacts with which mens being able run with lower chlorine perfectly safely and lower chlorine will lead to less pH rises.  Pucks are formulated to work in plaster pools with the industry std level of alkalinity if they are used in low alcalinity pools like mine then the pH could also be an issue through what the industry calls bounce but bounce is false it doesnt bounce it moves in accordance to the amount of acid/alkali added andwith lower alkalinity it takes a lot less to move it but it doesnt drift upwards toward 8.4 it can days to get to 7.8 with my air blower running which is to actually being used to test pH canges over time.

    There are loads of things wrong in the pool industry and I cant see a one size fits all approach when vinyl pools can be so much easier to maintain with low alkalinity.

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