Total Alkalinity is the measurement of the concentration of all alkaline substance that dissolve in water.
Total alkalinity is used as a measure of how much alkaline there is in the water. So, in swimming pool water, you should be concerned with bicarbonate alkalinity. This should be between 80 ppm and 120 ppm. So, if the total alkalinity is within this range then it will prevent rapid pH changes and will stabiles the pH level in the water.
So if the total alkalinity is too low then marbelite and plaster walls will become etched, metals corrode and your pools walls and floors could stain. Also the water could turn green, people’s eyes can burn and the pH bounce (pH rapidly going up and down randomly). But if TA is too high than the pH will be difficult to adjust, so than the water will become cloudy, the pool constantly needs acid and the chlorine loses its efficiency as a disinfectant.
You must test for Total Alkalinity regularly.
If you need to raise the level of Total Alkalinity than you use sodium bicarbonate. You should use this because it’s the only chemical that will increase TA without increasing the pH. Note that you should only add sodium bicarbonate at the rate of 1 kg per 50,000 litres of water every 4 days.
To lower your the levels of TA can take a while to do. You would need to add Acid, either liquid or dry to the deepest part of the pool with the filter on. It takes a while to lower the levels of TA because the acid should only be added a little at a time and you must dilute before pouring it in the pool. Then you need to wait 3 days between applications, and it could take days or weeks for the TA to reduce if the levels where very high to begin with.