Swimming Pool pH Chemicals
What is pH?
The pH (always written with a lower case p and an uppercase H) is the acidity level of a substance. It is measured on the pH scale which goes from 0 to 14. At one end of the pH scale is 14 which is very acid and at the other end zero is very alkali. In the middle is the pH value of 7.0 which is neutral. In a swimming pool the ideal pH level is 7.2 to 7.4. A pH in between 7.0 and 7.8 is OK but lower than 7.0 or higher than 7.8 is bad. The pH level in your swimming pool is very important. It is usually referred to as the "pH balance" because you are always trying to achieve the correct balance between acid level and alkali level.
Why is the pool pH so important?
There are a number of reasons why getting the pool's pH right is important.
- Incorrect pool pH can lead to eye irritation in bathers.
- The chemicals used to keep the water clean work best if the pool pH is correct.
- High pH levels (alkali) can lead to the pool walls and pool equipment scaling up with deposits of calcium.
- Low pH levels (acid) can lead to damage to pool walls as the grouting or plaster is leached out. Metal objects will be corroded and bathers skin can be dry and itchy.
What to do if your pool pH is too high.
In most of the South of the UK the source water in the taps has quite a high pH (alkaline). Consequently pool owners have to add pool acid to lower the pH. The chemical most often used is known as Dry Acid. Also called pH Minus or pH reducer the actual chemical name is Sodium Hydrogen Sulphate. Dry Acid is the preferred chemical because it is in dry, granular form. Liquid Acid can be used but, unlike dry acid, it is quite dangerous to handle. Add pH Minus according to the instructions on the product. You may need quite a lot, tens of Kgs over the course of a season is not unusual in some areas.
What to do if your pool pH is too low.
Water with low pH (acid) is found in areas where the source water comes in off mountainous areas. Scotland, South Wales and Northern areas often have low pH levels. To correct this you need to use a chemical commonly known as Soda Ash. Also known as pH Plus or pH Increaser the chemical name is Sodium Carbonate. Don't confuse this with Sodium Bicarbonate as used for stomach upsets but Sodium Bicarb is used in swimming pools to control Total Alkalinity. More on that below. Add pH Plus according to the instructions on the product.
How do you test for pool pH?
Knowing what the pH level of your pool water is requires a simple test. There is more on how to carry out the test and the various testers in the pool water testing section. The testers usually test for Chlorine level and Total Alkalinity too.
What is Total Alkalinity?
Total Alkalinity (known as TA) is closely related to pool pH balance. The ideal level for TA is 80 to 120. It is a complex subject and we go in to it in greater depth in our blog posting on Total Alkalinity. If your TA is too low you can easily raise it by adding the chemical know as Alkalinity Increaser who's chemical name is Sodium Bicarbonate. The same chemical as used for stomach upsets but cheaper, non-food grade quality is used in swimming pools. Lowering TA is not so easy. Refer to our blog posting for more on this subject (link above).