What is total alkalinity and why is it important.
Pool owners are often confused by “total alkalinity” and how it relates to pH. Total Alkalinity and pH are important and while related need to be checked separately.
If the total alkalinity is too low
||pH is a measure of whether the pool water is acidic or alkaline (or somewhere in the middle). pH is important because if not correctly adjusted, chlorine may not effectively sanitise the pool. A healthy pool should have a pH between 7.4 and 7.6
||Total alkalinity on the other hand is a measure of the overall alkaline substances in the water. Its important because unless adjusted to the correct level, you will find it is difficult to maintain the pH at the correct level.
Basically, the pH of the pool can “bounce around”. The total alkalinity of the pool should be adjusted to between 80 and 120 parts per million (or ppm).
, the pH will tend to bounce (pH rapidly going up and down, seemingly at random). The pool surface itself can experience etching and staining.
If the total alkalinity is too high
, the pH is difficult to adjust, the water becomes cloudy, the pool constantly needs acid (according to your test kit) and the chlorine loses its efficiency as a disinfectant.
Who tests total alkalinity, and how often
Many pool owners with “larger” test kits perform total alkalinity tests at home. Alternatively, most pool shops with water testing services will perform this test.
Whereas pH is normally tested weekly, total alkalinity (once corrected) tends to be checked every couple for months.
How to adjust Total Alkalinity.
To raise the level of total alkalinity (if below 80ppm)
We add sodium bicarbonate (ordinary “Bi-Carb Soda”, often sold as pH Buffer). Note that you should only add sodium bicarbonate at the rate of 1 kg per 50,000 litres of water every 4 days. Raising the total alkalinity can therefore be quite a time-consuming, slow process.
Lowering the total alkalinity
This is also a slow process. Ordinary pool acid is added to the deepest part of the pool with the filter off. The acid should only be added a little at a time (no greater than 1 litre each dose). Wait 3 days between applications. It could take days or even weeks to reduce the total alkalinity, if it is very high.
Finally, if you are adjusting both pH and Total Alkalinity, remember adjust the Total Alkalinity first and fine tune the pH later.