pH and your Pool: Why is your pH High or Low

pH is the most important test factor for you swimming pool and if it gets out of balance there are many negative effects that you will encounter. The ideal pH is 7.5 but it can be as low as 7.2 and still be fine. Most experts agree that 7.4-7.6 is the range the pH should be maintained at in your swimming pool.

pH (7.2-7.8)
The pH of the water, determines if it is acidic or basic. Either extreme can have disastrous effects on the pool finish, equipment, or plumbing. When the pH is out of range, bathers may complain of eye discomfort or other ailments.

An acidic pH will cause the water to become aggressive. It will etch the plaster and cement finishes around the pool. Worse yet, it will dissolve the metallic components of the pool. The most expensive metallic component is the copper heat exchanger within the pool heater. The ideal range for the pH again is 7.4 - 7.6 (though 7.2 - 7.8 is acceptable).

Low pH will cause:

Corrosive Water

Stains

Etched plaster

Eye & Skin Irritation

Cloudy Water

Increased Chlorine Activity

Destruction of Total alkalinity

Stretching of Vinyl Liners

Blistering of Fiberglass Pools

High pH will cause:

Scale Formation

Stains

Cloudy Water

Short Filter Cleaning Cycles

Eye & skin Irritation

Poor Effective Chlorine

So you can see that keeping your pH in balance is very critical. If the pH gets too high or too low it can have damaging effects on your pool.

Testing for pH:

Testing once a week is ideal. For a new pool start up testing daily for the first two weeks is recommended. But once a week will give you a good indication of how stable the pH is in the pool water. There are various ways of testing the pH; test Strips, basic test kits and Taylor Kits that use reagents. Alternate testing can be done with the ColorQ Pro7 Photometer testing and Digital pH testers.

The most common way to test is with Phenol Red. It is a reagent drop test that is very accurate. The color of the reagent in water will indicate if the pH is high or low. Digital Testers and testers that use a photometer will give you an exact digital readout of the pool pH. These are good for those who have trouble with the color scale of the reagent testers.

Lowering high pH:

If the pH starts to get high in your pool the only way to lower is by adding acid. Either a dry acid or liquid acid. Muriatic Acid of 31.45% is the most common acid used to lower the pools high pH. Dry acid or Sodium Bisulfate is the dry form of acid that can be added to lower the pH. Some test kits like the Taylor K-2006 will have an Acid Demand Test. This is a reagent test that will tell you how much acid to add to your pool to lower the pH. A chart is included with pool gallons and how many pint or quarts to add depending on the test results.

Raising low pH:

If your pH is low you can raise it up using a base. A base is the opposite of an acid and it will raise the low pH up in your pool rapidly. The best base is Borax as it will raise the pH without raising the Total Alkalinity. Baking Soda (Sodium Bicarbonate) works well also but it is mainly used for raising the Alkalinity and requires large amounts to raise the pH. Soda Ash (Sodium Carbonate) raises the pH well but it also raises the pools Alkalinity up so use Soda Ash if Borax is not available in your area.

Pool Surface Types and pH:

One thing often overlook when discussing pH is the pool surface type. Since cement has a high pH of 12-13 – some plasterers even say closer to 14, the Acid Demand will be high since the plaster is very base. That is why when a newly plaster pool is curing in the first 6 months it seems like you are adding tons of acid every week to keep it low.

A Pebble Tec pool will be less base and more acidic as the surface is basically made up of river rocks. You will notice that in a Pebble Tec pool the Acid Demand is lower than a plaster pool. Vinyl and Fiberglass pools are basically a piece of plastic and plastic has a low pH around 6. That is why you rarely need to add acid and in fact find yourself adding Base to raise up the pH when it drops low. Tile pools also have a lower Acid Demand but slightly higher than Vinyl and Fiberglass.

Types of Sanitizers that affect pH:

The three main chlorine sanitizers that affect pH are 3” Trichlor Tablets, Salt Water Generators and Cal-Hypo (Calcium Hypochlorite). Trichlor Tablets have a very low pH around 2 so using these frequently will lower the pools pH. That is why they are not recommended for Vinyl and Fiberglass pools. Salt Water Generators increase the pools pH as they convert the salt into chlorine. Sometimes to astronomical levels. And Cal-Hypo has a high pH and if you use this as your primary sanitizer the pH and Calcium Hardness will rise.

So be aware that these three sanitizers affect the pH in your pool. Liquid chlorine or bleach has the least affect on pH and Trichlor shock with a pH around 4 also has a minimal affect since it is quick dissolving. Dichlor is pH neutral so it doesn't really move the pH one direction or another.

Alkalinity:

Regardless of your water source all water will contain some alkaline materials. The amount will vary depending on your water source. Alkalinity is the water's ability to neutralize acid. Total Alkalinity is the measurement of the water's resistance to a change in the pH. Alkalinity and pH are closely tied together and are interconnected.

I will touch on this more in a separate article but the Alkalinity is important to prevent pH bounce. This is where the pH rises or falls rapidly. Know that the pools Alkalinity level is important and to prevent pH bounce the ideal range is 80-120 ppm.

pH and Chlorine:

One final note about pH. If the pH is in the ideal range of 7.4-7.6 the chlorine kill rate will be most effective. This means the chlorine will quickly kill bacteria and viruses. If the pH is lower than 7.2 it will be strong but will be used up faster. If the pH is over 8.0 the Chlorine is less effective and has a slower kill rate. You will also notice more algae with a high pH even if the pool is showing good chlorine levels.

So you can see the pH has a wide range of affect in your pool water. Check it weekly and keep it balanced and you will see many of your water issues corrected and resolved.