Testing for pool alkalinity is critical for ensuring your pool's water is optimally balanced. Alkalinity, also referred to as "total alkalinity," is measured in parts per million (ppm) and refers to the strength or intensity of the alkaline substances in your pool's water. Essentially your pool’s alkalinity is a measure of resistance, or rather how difficult it is to make changes to your pool’s pH.
For example, when the TA or the water’s resistance to changes in pH is low, the pH will fluctuate since, in this scenario, the water’s pH level is vulnerable and can be easily influenced by everything it comes in to contact with, whenever you use your pool normally.
How pH Affects Your Water
A pool’s pH is a scale that measures the acidity of your swimming water. The pH scale ranges from 0 to 14 with 7.4 being the ideal pH level for pools. A pH level that is too high means the water is basic or lacking in acid. If your water reads as too low on the pH scale, then it is considered too acidic.
Maintaining a reading that is close to neutral 7.4 is important.
The process of selectively raising or lowering your pool’s alkalinity is called buffering, because in a sense you are putting a buffer around your pH levels, trying to hold them within a stable range.
Pools that have unstable pH readings that sway too far on either end of the spectrum can cause your chlorine to lose its effectiveness as a disinfectant, turn your water cloudy, irritate eyes, and cause dry skin. Low pH conditions will etch pool walls, corrode metal, and turn water green.
Since alkalinity plays a buffering role in your pool water’s health, the other chemicals and substances in the water are always going to be working against it. For this reason, it’s unlikely that your alkalinity will be too high and it’s much more likely that it will be too low or approaching lower levels that need to be raised. If by some chance your alkalinity is exceptionally high, you can tone it down by adding muriatic acid to the water, but this is risky if you’re a pool novice. Try to just wait. Total Alkalinity will tend to drop over time.
However, if your alkalinity is too low, it is important that you take the appropriate steps to change it.
Step 1 - Test Your Pool Water
Using a pool water testing kit, dip the water collector under the water to a depth of 12-18 inches. Pull the collector out of the water and make sure the water is filled up to the fill line on the collector.
Add your reagents as instructed in your water testing kit's provided manual. Be sure to add a chlorine neutralizer to the sample to get the best reading, as chlorine can often affect the pH level readings. Depending on the kit you've purchased, you may have to add a cover to your collector and shake it to mix the reagents with the water. If you've used test strips, the instructions will likely advise you to wait 20-30 seconds for the best reading.
Check the color against the chart provided with your kit. Paying close attention to the pH level readings, note if the level is within 80-125 ppm for gunite or concrete pools, or 125-170 ppm for painted, vinyl and fiberglass pools. In other words, your pH level should be between 7.2 and 7.6 respectively on the litmus scale. If so, you don't need to take any further action.
Note: Depending on which kit you are testing with, there may also be a scale that is telling you your chlorine levels. It is always a good idea to look at those results to be aware of everything going on in your pool, but the chlorine test will not have any bearing on how you alter your alkalinity levels.
Step 2 – Convert to PPM
If your water test shows your TA is too low (below 80 ppm or 125 ppm depending on your pool type), you'll need to raise it by adding sodium bicarbonate. Use the chart that came with your water testing kit or pool chemicals to determine how much sodium bicarbonate to add.
If you are still confused about measuring parts per million (ppm), it is simply a ratio. For example, we’re measuring the sodium bicarbonate in pounds but our pool water in gallons. So, to reliably find the right amount of sodium bicarbonate to use, you will need to know the amount of water in your pool in pounds.
Now ideally, you are aware of how large your pool is at least in a measurement of gallons. Given that we are trying to convert this into parts per million, it’s important to know how many gallons of water it takes to weigh out 1 million pounds.
120,000 gallons of water is the mass equivalent of one million pounds. So, that means that if you had a 120,000 gallon pool in which the water weighed exactly 1 million pounds, you would add only one pound of sodium bicarbonate to the water to increase the alkalinity by 1 ppm. The ratio is now more obvious as it is 1 pound of sodium bicarbonate per one million pounds of water.
If your pool has a different gallon capacity, just do the math and maintain that ratio (i.e. 240,000-gallon pool would get 2 pounds of sodium bicarbonate, a 60,000-gallon pool would only get a half of a pound of sodium bicarbonate).
WARNING: Sodium bicarbonate can only be added at a rate of 2.2 pounds for every 11,000 gallons of water every four days. This means you cannot add the entire quantity of sodium bicarbonate in one session; the process must be spread out.
Add Sodium Bicarbonate
Turn your pump off and put on your eye protection and gloves. Broadcast the sodium bicarbonate by shaking or sprinkling it into the deep end of the pool. Don't just dump it into the pool. It will clump and sink, taking longer to disperse. Leave the pump off for two hours, then turn it back on.
Retest And Reapply
Retest after three or four days. Test your pH levels as well as your TA levels because sodium bicarbonate and any other chemicals will affect the pH balance.