Total Alkalinity

Total alkalinity is a measure of the total alkaline substances found in the pool water. For swimming pool purposes we usually determine the carbonate content of the water by measuring the level of calcium carbonate. Total Alkalinity (TA) should usually be kept at 80 - 120 ppm, though in high alkalinity waters this is often hard to achieve without resulting in an abnormally low pH. The results of a low TA may be one or more of the following:

• etching of the plaster, marbelite, marcite or tile grouting
• corrosion of metal parts (pool heater, steps, scoop pole, etc.)
• staining of the pool's surfaces
• green water
• burning eyes and itchy skin
• pH bounce (rapid fluctuations in pH)

What is alkalinity?

Raising Low Total Alkalinity

Sodium bicarbonate (bicarb) will raise the TA without excessively raising the pH. Regular pH-up will raise the pH as well as the TA and should not be used. Care should be taken to increase the TA over a period of time, adding a maximum of 1 pound of bicarb for each 6,000 gallons of water. The bicarb can be added at this rate every 4 days, until the required level is reached. The results of high TA may be one or more of the following:

• pH keeps going up despite regular addition of pH-down
• cloudy water
• burning eyes and itchy skin
• reduced chlorine efficiency resulting in algae growth

Lowering High Total Alkalinity

Regular small "acid shocks" with pH-down will reduce the pH while lowering the TA. This can be an extremely slow process and it may take weeks or longer to reduce high TA. One suggested method is as follows:

• turn off the pumps and allowing the water to settle
• slowly add the pH-reducer into one spot in the deep end of the pool
• allow the chemicals to "burn off" some of the alkalinity for 15 - 30 minutes (You may notice some bubbles rising to the surface. This is carbon dioxide and is indicative of the destruction of excess alkalinity.)
• turn the pumps back on and allow the water to mix thoroughly

The above method should be used only when the pH is high and your pool requires pH-reducer. If the pH is normal, adding a shock will reduce the pH to undesirable levels resulting in further pool problems. Care should be taken not to let the pH-reducer sit for too long as it will begin etching and softening the plaster, marbelite, marcite or tile grouting. It is also recommended to dilute the pH reducer in a bucket of water before adding to the pool to prevent this problem from occurring.