Shocking a pool is a common practice to keep the water clean and safe. Shocking involves adding a large dose of chlorine or another oxidizer to the pool to destroy contaminants such as bacteria, algae, and organic matter. But does shocking a pool lower alkalinity? And why does alkalinity matter in the first place?
What is Alkalinity and Why is it Important?
Alkalinity is a measure of how well the water can resist changes in pH. pH is a measure of how acidic or basic the water is. The ideal pH range for pool water is between 7.2 and 7.6, which is slightly basic. If the pH is too low (acidic), it can cause corrosion of metal parts, irritation of skin and eyes, and reduced chlorine effectiveness. If the pH is too high (basic), it can cause scaling of pool surfaces and equipment, cloudy water, and reduced chlorine effectiveness.
To prevent drastic fluctuations in pH, pool water needs to have some buffering capacity. This is where alkalinity comes in. Alkalinity is mainly composed of bicarbonates, carbonates, and hydroxides in the water. These substances can neutralize acids or bases that are added to the water, thus keeping the pH stable. The ideal alkalinity range for pool water is between 80 and 120 parts per million (ppm).
How Does Shocking Affect Alkalinity?
Shocking a pool does not lower alkalinity directly. Alkalinity is related to the buffering capacity of the water, which helps to control pH. When a pool is shocked, it is raising the chlorine level, which means it is increasing the disinfection level of the water.
However, shocking a pool can affect alkalinity indirectly by affecting pH. Depending on the type of shock used, shocking can either raise or lower pH temporarily. For example, calcium hypochlorite (cal-hypo) shock has a high pH of around 12, which can raise the pH of the pool water. On the other hand, sodium dichloro isocyanurate (dichlor) shock has a low pH of around 6, which can lower the pH of the pool water.
When the pH changes, the alkalinity may also change as a result. This is because some of the alkaline substances in the water may react with acids or bases to form different compounds. For example, when the pH is low, some of the bicarbonates may react with acids to form carbon dioxide and water, thus lowering alkalinity. When the pH is high, some of the carbonates may react with bases to form bicarbonates and hydroxides, thus raising alkalinity.
However, these effects are usually temporary and minor, as most shock treatments wear off quickly and do not significantly alter the total amount of alkaline substances in the water. Therefore, shocking a pool does not have a major impact on alkalinity in the long run.
How to Lower Alkalinity in a Pool?
If your alkalinity is too high (above 150 ppm), you may need to lower it to prevent problems with your water chemistry. The most effective way to lower alkalinity in a pool is to use muriatic acid or sodium bisulfate (pH reducer). These substances are strong acids that can neutralize some of the alkaline substances in the water, thus lowering both pH and alkalinity.
To lower alkalinity in a pool using muriatic acid or sodium bisulfate, follow these steps:
- Test your pool water using a test kit or test strips to determine your current pH and alkalinity levels.
- Calculate how much acid you need to add to your pool using an online calculator or a chart provided by your product manufacturer.
- Turn off your pool pump and heater.
- Pour the acid slowly into one spot in front of a return jet in the deep end of your pool. Avoid splashing or spilling the acid on yourself or your pool surfaces.
- Wait for at least 30 minutes before turning on your pool pump and heater.
- Test your pool water again after 4 hours to check your new pH and alkalinity levels.
- Repeat the process if necessary until you reach your desired levels.
How to Restore Your pH Level Without Raising Alkalinity?
If you use acid to lower your alkalinity, you will also lower your pH. However, if your pH drops below 7.2, you may need to raise it back to the ideal range without raising your alkalinity again. The best way to do this is to aerate your pool water.
Aeration involves adding air bubbles to your pool water using an air pump, a fountain, a waterfall, or any other device that creates agitation on the surface of the water. Aeration increases the rate of carbon dioxide outgassing from your pool water, which raises the pH without affecting the alkalinity.
To raise your pH using aeration, follow these steps:
- Test your pool water using a test kit or test strips to determine your current pH level.
- Turn on your aeration device and let it run for several hours or until you see a noticeable increase in your pH level.
- Test your pool water again to check your new pH level.
- Adjust your aeration device as needed until you reach your desired pH level.
The Bottom Line
Shocking a pool does not lower alkalinity directly, but it can affect it indirectly by affecting pH. However, these effects are usually temporary and minor, as most shock treatments wear off quickly and do not significantly alter the total amount of alkaline substances in the water. Therefore, shocking a pool does not have a major impact on alkalinity in the long run.
If you need to lower your alkalinity in a pool, use muriatic acid or sodium bisulfate (pH reducer). These substances are strong acids that can neutralize some of the alkaline substances in the water, thus lowering both pH and alkalinity. If you need to raise your pH without raising your alkalinity, use aeration. Aeration increases the rate of carbon dioxide outgassing from your pool water, which raises the pH without affecting the alkalinity.