pH is the most important element in swimming pool water chemistry - it affects every other chemical balance in the pool water. pH is a scale for measuring the pools acidity or alkalinity level. The pH level indicates the relative acidity or alkalinity of your pool water. pH is measured on a scale from 0 (strong acid) to 14 (strong alkaline) and pH neutral is 7. In pools a slightly alkaline level between 7.2 & 7.6 is ideal because this range is the most comfortable to the human eye, provides optimum use of free chlorine and provides water that is not corrosive or scale forming.
If pH falls too low (below 7)
- Water becomes acidic, eye & skin irritation occurs.
- Corrosion - Heater element may corrode (unless you have Titanium heating elements) the pump impeller & other metal fittings on the pool will corrode.
- Dissolved metals may leave stains on the walls. Rapid loss of alkalinity and wrinkling of Liner.
If pH is too high (above 8)
- Chlorine activity is slowed and inefficient. Scale formation and discolouration of pool walls.
- Water becomes cloudy and the filter is overworked & may become clocked.
- Eye & skin irritation may occur.
Pool water needs to be sanitised to ensure bather safety. Bacteria will rapidly multiply in pool water that remains untreated / unsanitised. The most widely used disinfectant (sanitiser) for domestic pools in the UK is currently Chlorine, we will discuss alternatives to chlorine during this guide. Your pool water should be maintained at the correct chlorine level at all times.
Total Alkalinity (TA)
Total Alkalinity is a measure of water’s resistance to change in pH – TA is the amount of alkali (not to be confused with alkaline) in the form of bicarbonates, carbonates and hydroxides present in the pool water. TA affects and controls the pH.
The ideal level for TA is between 80 and 140 parts per million (ppm)
If the TA is too high:
- The pH will be difficult to adjust.
- A High pH level often occurs.
- This causes cloudy water, decreased disinfectant effectiveness, scale formation & filter problems.
If the TA is too low:
- The pH will be unstable and difficult to maintain.
- pH changes rapidly when chemicals or impurities enter the water.
- pH may drop rapidly causing etching & corrosion.
How Does TA Affect the pH Level?
In basic terms TA acts like a buffer for your pH level. If you picture a playground seesaw as the pH indicator, and you place 2 people of the same weight on either end - the seesaw balances which relates to pH neutral. The people are representing the TA and if one of these people were to get off of the seesaw this would cause a massive change in the pH level one way or the other. Now picture the same seesaw with 10 equally weighted people on either side, the pH is again balanced but now if one person were to get off of the seesaw the balance would not change as drastically due to the 9 remaining people acting as a counterbalance. There are a number of products available such as T.A
Water Hardness / Calcium Hardness
Water hardness depends on the amount of dissolved calcium in the pool water. High levels will give rise to scale formation whilst low levels cause corrosion to pool surfaces & equipment. The water hardness should be maintained at a minimum level of 200ppm. Water hardness can be increased by using a water hardness increaser such as Hardness Plus. Unfortunately the only way to reduce water hardness is to dilute the existing pool water.
Testing Your Pool Water
To ensure that your pool water is a safe and clean environment you will need to spend a short time testing the water chemistry & if required, adding the appropriate water treatment products.
There are several types of testers available:
• Test Strips – (Litmus paper) are the simplest and quickest means of testing your pool water for chlorine & pH.
• Liquid Reagent – Care needs to be taken with this type of test kit to ensure the correct amount of reagent is added.
• Test Tablet – These kits are probably the best means of testing your pool water; they offer simple, accurate analysis at an affordable price. You should check your pool water daily for both sanitiser and pH. Total alkalinity should be tested on a weekly basis & the water hardness should be tested on a monthly basis.