Maintaining proper pool water chemistry is crucial for keeping your pool clean, safe, and inviting. One important aspect of pool maintenance is monitoring and adjusting the alkalinity of the water. Alkalinity refers to the ability of water to resist changes in pH. The recommended alkalinity level for a swimming pool is between 80-120 ppm (parts per million).
Baking soda, also known as sodium bicarbonate, is commonly used to raise total alkalinity levels in pools. But how often should you add baking soda? There are a few factors to consider when determining the ideal frequency for adding baking soda to your pool.
How Alkalinity Affects Pool Water
Alkalinity serves as a buffer that prevents drastic fluctuations in pH. Water with low alkalinity is prone to pH bounce, where the pH level spikes up and down. Rapid changes in pH can corrode pool surfaces, irritate eyes and skin, and require frequent additions of acid or base to stabilize the water.
On the other hand, water with high alkalinity is resistant to pH change. This may seem desirable, but it can become difficult and require large amounts of acid to lower pH in high alkalinity water.
The ideal alkalinity range allows for stable pH with smaller amounts of pH up/down chemicals. With proper alkalinity, regular minor pH adjustments can easily keep the water in the optimal pH range of 7.4-7.6.
Factors That Affect Pool Alkalinity
There are several factors that cause alkalinity levels to rise and fall in a swimming pool. Understanding what impacts alkalinity will help determine how often baking soda needs to be added.
Makeup Water
The main source of water added to pools is the fresh water used to fill it up and replace water lost due to splashing, backwashing filters, draining, and swimmer use. The alkalinity level of this makeup water will directly influence the overall alkalinity of the pool.
Municipal water supplies generally have moderately low alkalinity in the range of 40-60 ppm. Well water alkalinity varies dramatically based on the geology of the location, ranging from 0 to over 400 ppm. Starting with low alkalinity makeup water means baking soda will need to be added more frequently.
Rainwater
Rainwater is naturally low in alkalinity, containing only trace amounts from atmospheric dust. For outdoor pools, heavy rains can dilute alkalinity each time the pool overflows. Indoor pools are less impacted by rain.
Chemical Additions
Certain chemicals added to pools can increase or decrease alkalinity levels. Most notably, sodium bisulfate (pH down) lowers alkalinity, while muriatic acid (hydrochloric acid) has no effect on alkalinity. Conversely, sodium carbonate (pH up) raises alkalinity. With routine additions of these chemicals for pH adjustment, alkalinity will gradually change over time.
Calcium Hardness
Pools with calcium hardness over 250 ppm may experience slow increases in alkalinity over time. This occurs as calcium carbonate precipitates out of solution. Calcium carbonate aggregates act as a mild base and slightly raise pH and alkalinity.
Measuring Pool Alkalinity
The only way to know your pool’s alkalinity level is to have your water tested. Pool testing strips provide a quick and convenient option for measuring alkalinity on your own. More accurate results can be obtained through pool stores or commercial labs using titration testing.
Plan to test the alkalinity at least weekly during pool season. Testing more frequently allows you to spot trends and make incremental adjustments before levels stray too far from the ideal range. Many pool owners find it helpful to record test results in a logbook.
Pool Testing Strips
Dip-style alkalinity test strips provide measurements in 10-20 ppm increments. To use, briefly submerge the strip in pool water, then compare the resulting color to the chart on the test kit container to estimate alkalinity level. Test strips have a margin of error around +/- 10 ppm.
Titration Testing
Titration testing is a volumetric analysis that provides highly accurate alkalinity measurements. The process involves adding an indicator solution to a sample of pool water, then slowly dosing with a dilute acid titrant until a color change signifies the alkalinity endpoint. A skilled technician can determine alkalinity within 1 ppm accuracy. At pool stores, alkalinity titration tests costs $5-10 per sample.
How Often to Add Baking Soda
How frequently baking soda needs to be added depends on your pool’s starting alkalinity, the makeup water source, and how rapidly the alkalinity decreases due to chemical additions and dilution.
As a general guideline:
– Test alkalinity at least once per week
– Aim to maintain an alkalinity level between 80-120 ppm
– If alkalinity falls below 80 ppm, add baking soda to raise it by 20-30 ppm
– Only add more if follow-up testing after 24 hours shows the desired increase was not achieved
– If alkalinity is still trending down after each addition, baking soda may be needed as often as every 2-3 days
– For pools with alkalinity dropping 50+ ppm per week, switch to sodium carbonate which boosts alkalinity more effectively per pound
The exact dosage of baking soda needed depends on the volume of water in the pool. Here is a dosing table:
Baking Soda to Increase Pool Alkalinity by 20 ppm
| Pool Size (gallons) | Baking Soda (lbs) |
|---|---|
| 5,000 | 0.5 |
| 10,000 | 1.0 |
| 15,000 | 1.5 |
| 20,000 | 2.0 |
| 25,000 | 2.5 |
| 30,000 | 3.0 |
| 35,000 | 3.5 |
| 40,000 | 4.0 |
Spread the baking soda around the pool perimeter and allow it to dissolve overnight before testing alkalinity again. Run the filter and brush the pool walls and floor to help distribute the baking soda. Manage pH, calcium, and cyanuric acid levels accordingly since raising alkalinity also impacts these parameters.
Troubleshooting Alkalinity Issues
Sometimes pools develop problems keeping alkalinity stable. Here are some troubleshooting tips:
Alkalinity Too High
If alkalinity creeps above 150 ppm, use muriatic acid or sodium bisulfate to lower it. Adding large doses of pH down chemicals will bring the alkalinity back into range. Prevent future spikes by reducing the baking soda dosage and frequency.
Alkalinity Too Low
Check that the test results are accurate by having a pool store validate. Increase the baking soda addition to 2 lbs per 10,000 gallons and test every few days. Switch to sodium carbonate if baking soda is not raising alkalinity adequately. Identify and address any dilution issues from new water additions or leaks.
Alkalinity Always Trending Down
Frequent alkalinity drops likely mean the makeup water has very low alkalinity. Change to a makeup water source with higher alkalinity. Or plan to add baking soda or sodium carbonate after every significant water addition or rain event. Reduce acid dosing frequency to slow the alkalinity decline between additions.
Alkalinity Fluctuating
Wide swings in alkalinity indicate improper chemical balance. Adjust maintenance practices to bring pH, calcium, and cyanuric acid to target levels before trying to stabilize alkalinity. Eliminate any extreme highs or lows in pH reading that could be rapidly dissolving alkalinity buffers.
Maintaining Proper Pool Alkalinity
While requiring some monitoring and chemical additions, keeping alkalinity in the ideal range is very achievable with a little effort. Here are some tips for easy alkalinity management:
– Test alkalinity weekly and record measurements
– Develop a routine baking soda addition schedule based on test trends
– Use sodium carbonate if you need larger alkalinity increases
– Reduce acid dosing if it is rapidly crashing alkalinity
– Validate readings and troubleshoot if levels are not responding as expected
– Balance pH, calcium, and cyanuric acid first before fixing alkalinity
– Communicate alkalinity adjustments to pool maintenance staff
Proper alkalinity is crucial for healthy pool water. Measure frequently, make careful baking soda additions, and balance related chemicals to maintain levels in the 80-120 ppm sweet spot. With some consistency and vigilance, you can keep alkalinity right where it needs to be.
Conclusion
The ideal frequency for adding baking soda to a pool varies based on the starting alkalinity, makeup water source, chemical additions, and degree of dilution. Test alkalinity at least weekly and add baking soda as needed to maintain a level between 80-120 ppm. Use 1-4 lbs of baking soda per 10,000 gallons to increase alkalinity by 20 ppm increments. Adjust the dosage and frequency based on the specific conditions of your pool. Maintain proper balance of pH, calcium hardness, and cyanuric acid as well. With routine testing and careful baking soda additions, keeping your pool’s alkalinity in the target range is straightforward. Proper alkalinity is essential for easy pH management and a sparkling clean pool.
