Muriatic acid has become an increasingly popular approach to maintain proper pH levels in swimming pools. Why? Because it is relatively inexpensive compared to other chemicals (running at about ten dollars per gallon depending on your favorite home supply store). Muriatic acid is truly hydrochloric acid (HCl) but a less pure and diluted version of it. Pure hydrochloric acid will serve the same strong acid, pH lowering purpose at a much higher cost to the pool owner.
That being said, handling corrosive acids is no joke; but when done correctly they will aid the longevity of a swimming pool through cleaning and well balanced pH levels to prevent unwanted side effects or expensive equipment maintenance.
Benefits of adding muriatic acid to your pool
By adding muriatic acid to a pool that has shown signs of increased pH levels, the muriatic acid will prevent calcium build-up, chlorine deactivation, and avoid leaving your precious waters susceptible to bacteria growth and other unwanted contaminants—eventually making it unusable. This pH maintenance will also prevent any unwanted health effects for swimmers, like skin irritation and other digestive tract issues.
What does muriatic acid do to a pool?
First, we need a quick recap of water pH. This value represents the hydrogen ion concentration in water. Scaled from 0 to 14, acids yield pH values below neutral 7, and bases will have pH values above 7. For example, pure water is a neutral 7 on the pH scale whereas muriatic acid can range from 1 to 2 depending on the concentration, meaning it is a very strongacid. In this way, if you add a little bit of muriatic acid to water the pH will drop. The changes can easily be measured using a water pH test kit for convenience of setup and actual measurement.
This is the key concept of using muriatic acid: adding measured amounts of muriatic acid to lower and manage pool pH levels and alkalinity (see next paragraph). In theory it is very simple, but background knowledge is necessary to perform this task safely and properly to keep everyone swimming along.
One more parameter to recap is alkalinity, or the ability of liquids to resist acidification. This parameter is commonly confused with describing a basic liquid (pH value greater than 7) and the terms should not be used interchangeably. It usually trends with pH, however, this liquid buffering capacity is created by carbonates and bicarbonates (baking soda!) dissolved in a liquid. Alkalinity allows the pH to stay relatively stable when you’re adding acidic substances, like chlorine and our new friend muriatic acid.
This can be a frustrating distinction for pool owners who attempt to change pH and nothing happens, or it changes drastically. Alkalinity and pH are also affected at different rates by different chemicals. In this way, it is always important to take water chemistry in small increments of change—which can be frustrating but much safer and more efficient in the long run. Thankfully alkalinity can be measured with various test strips and electric probes to achieve an alkalinity of around 100 ppm (parts per million) to 150 ppm.
Overall, pH is easier to measure and a more accessible value in indicating a healthy pool, but alkalinity also influences pH so must be considered and balanced. Alkalinity can be controlled by adding baking soda, or other store bought chemicals, to a pool while at neutral-ish pH. That being said, this article will focus primarily on pH and muriatic acid (Note: pH should be at relatively neutral pH levels, 7-7.4, before altering alkalinity to avoid a large shift in either parameter).
What are healthy pool pH levels?
Healthy pool pH levels will be slightly basic around 7.2 to 7.8, this is the optimal range for swimmer comfort, pool longevity, and active chlorine percentage. pH values above this range will decrease the active chlorine significantly and lose the disinfectant properties that are necessary to kill bacteria and algae, and other human wastes.
This increase in pH will not be as hazardous to human health as an acidic pH would be; but as the pH rises and the chlorine stops working, the pool water can become cloudy, start to scale, and ruin the pool equipment altogether due to calcium deposits.
What is pool scale?
Scaling, or pool scale, refers to the point where water becomes too basic and calcium starts to solidify, giving a soft and flaky look to the water. This phenomenon can be readily observed along the pool walls, at the water line, as a white flaky buildup or “scales.” Pool pH levels can rise naturally over time due to high alkalinity; but if your pool reaches this point it is important to act in order to maintain the lifetime of your pool. This is where muriatic acid comes in.
How do I know if my pool pH levels are too high?
As discussed previously, if you visually see the scaling phenomenon, the pool pH is too high. But nobody wants to get to this point. Thankfully, pH is a very measurable characteristic of pools. This can be done with many different pH probes but it is important that you have one that works and ideally one that will read to at least one tenth of a decimal place (0.1).
To test, place a pH test kit in the pool water and wait for a reading (hopefully in the optimal range of 7.2 to 7.8). Note: do not forget to calibrate your pH probe! This is a very important step of pH measurements.
Once a reading is achieved, the value will inform you of how to act next (i.e. if your pH is outside optimal levels) and this will always be the first step in knowing if your pool pH and overall pool health is trending in the wrong direction.
How to add muriatic acid to a pool
1. Test the pH of the pool water using a pH probe.
It’s best practice to test the water a couple of times a week using a pH probeto catch any rapid changes in water chemistry. At this step, if your pH is too high then muriatic acid will be the best bet for lowering pool pH into healthy levels. Again, if alkalinity and pH are both off, first attempt to bring the pool pH slightly below optimal levels since adding alkaline substances will increase alkalinity and also pH (albeit a smaller increase).
2. Determine pool volume and the required amount of muriatic acid.
Keep in mind, lowering pool pH should be done incrementally for best results. Other pool pH decreasing chemicals can be found and advertised but muriatic acid will be the most cost effective option.
If the volume of the pool is unknown, a little math will save the day for once. Depending on the shape (we will assume a rectangle for now), simply measure the length, width, and average depth of the pool. Multiply all three to obtain cubic feet. Then, multiply cubic feet by 7.5 to get the total number of gallons.
Length x width x average depth x 7.5 = total gallons
Note: if the pool has a sloped bottom use the average depth between the shallow and deep end. If the pool has a sharp drop, consider splitting the pool into two parts for a more accurate calculation, and then add the two parts together.
3. Wear proper protective equipment (eye protection, gloves, clothes to cover skin). Do not skip this step!
Muriatic acid is a strong corrosive acid that can severely burn your skin, eyes, and any other living creatures. The fumes can also cause issues with lunges and breathing, so avoid direct inhalation.
Large rubber gloves that reach your elbow, lab goggles, aprons, closed-toe shoes, and full clothes are best practice when dealing with acid. Better safe than sorry in this scenario.
4. Dilute the acid to the desired level using the acid label or an online calculator.
Using a plastic bucket, fill it halfway with water and begin adding your acid carefully. Always add the water first to avoid acid splashing and other dangerous chemical reactions. Think, “acid to water, always acid to water.”
Depending on the acid concentration, a 1:10 ratio of acid to water is the ideal condition. If using a standard 5-gallon bucket that is half full with water, 4 cups or 1 quart would be the ratio equivalent to 1:10. Glass liquid measuring cups are great for this task as they provide easy measurement and pourability. On the other hand, an online calculator will be able to provide more detailed amounts of muriatic acid if necessary.
Beware inhaling any of the muriatic acid fumes, or splashing any on yourself or the surrounding area. Accidents do happen, however, so it’s best to have baking soda nearby to quickly pour on any spilled muriatic acid to neutralize it, and then clean up the residual. Keep in mind muriatic acid can damage concrete too, so don’t let it sit!.
At this point you should safely have a mixture of water and muriatic acid in a bucket. Give it a little mix with a plastic or wooden stirring device; and always avoid splashing any out.
5. Turn the pool on
To increase water circulation and enhance muriatic acid dispersion throughout the pool, it is best practice to turn the pool on before adding acid if you’re trying to lower the overall pH. By having the pump on it will aerate the pool, slightly increasing pH and aiding alkalinity. Therefore, adding muriatic acid to the pool while the pump is running will reduce the likelihood of large drops in pH. Remember, the name of the game in pool chemistry is sequential steps, not large changes.
Equally important, by turning the pool on the acid will constantly mix. This tactic will prevent acid from “pooling” on the bottom of the pool and degrading the pool floor. Again, have we mentioned that this is a strong acid? However, this concept of pooling can be used to largely increase the alkalinity of the pool without altering pH as much. A few minutes with the pool off after you add the acid can be beneficial to alkalinity, but always turn your pool on shortly after to avoid severe damage to the pool floor.
If you are still nervous about the pool floor being eaten by the acid, gently scrub the pool bottom as the acid mixes.
6. Add muriatic acid to the pool
Once your mixture is safely created and the pool is on, slowly add the acid and water mixture to the pool. For quicker mixing, pour the bucket contents around the edge of the pool while slowly walking around the pool. This will also help aerate the mixture as discussed in step 5.
Once the bucket is empty, always thoroughly clean it of acid. Again, a little baking soda will help neutralize the acid and avoid any accidents in rinsing and cleaning. Even the small amount of acid that could be in the bucket can cause large reactions and burns, as discussed previously. Even if the bucket has been cleaned 800 times, it’s best to only use that bucket as the muriatic acid pool bucket (just in case any acid is leftover). Use a marker and write “muriatic acid bucket” or some other catchy name that will indicate use for muriatic acid only.
7. Wait and repeat
The pump should run for at least half an hour to thoroughly mix the muriatic acid as it diffuses around the pool. If you’d like to aerate the pool longer and increase the pH a bit, keep running the pump or use an aerator/air stone to oxygenate the pool water. Dissolved oxygen probes are also very useful in determining the amount of aeration necessary. This method of aeration also helps reduce the pool from changing pH or alkalinity in large steps.
The morning after steps 1-6 were completed to add muriatic acid to a pool, start from step 1 and test the water with your favorite pH probe. And the process begins once again! Remember to test your pool pH several times a week even if the pool pH and alkalinity are at healthy levels.
Other factors to consider
Overall, different chemicals can be used besides muriatic acid to achieve healthy pool levels, but muriatic acid is the most widely used due to its inexpensive nature and proven effectiveness in cleaning and maintaining healthy pools.
Again, baby steps are best in altering pool water chemistry. It is not unlikely for this process to take 2-3 rounds of adding acid to the pool. Although beyond that, one should consider calling a professional or bringing in a water sample to your local pool store for advice.
If after one round of adding muriatic acid to a pool and the pH drops too low, before panicking keep the pump and/or aeration devices running. This will slowly raise the pH over time. Remember, pH is unstable and susceptible to changes. If nothing happens in a day or so, consider rechecking alkalinity or using pH increasing chemicals (in very small amounts). Lastly, it is crucial not to use the pool if pH values drop too low, which can be very harmful to human health.
If this all seems too much or you just hate the word chemistry, consider other pool options like saltwater pools. These may require more initial setup and less opportunity for non-professional maintenance, but overall require much less chemicals and can be much softer on swimmer skin. This is also an option for those allergic to chlorine.
In summary, it is extremely important to maintain proper pH and alkalinity levels of your swimming pool. This preventative maintenance will increase the longevity of your pool equipment by reducing algae growth, calcium deposits, and other particulates from damaging equipment and pool exterior. It will also increase swimmer comfort and reduce the likelihood of health conditions that can arise from incorrect pool maintenance. Namely, skin irritation, digestive tract discomfort, and/or other bodily pH issues. A healthy body yields a similar, slightly basic, pH level as a healthy pool.
In this manner, the importance of frequently measuring the pH of a pool to uncover signs of unhealthy pH levels cannot be understated. Fixing these pool parameter levels can be simple, but it requires a little background knowledge, a pH probe, chemicals (plus safety!), some time, and some effort. Don’t rush this process, however, and your pool will be healthy for adequate use and relaxation all summer long.
If you are unsure exactly which type of pH probe or testing kit will best suit your needs, do not hesitate to reach out to the world-class team at Atlas Scientific for more information.
pH probes contain two electrodes (a sensor electrode and a reference electrode) that measure the hydrogen-ion activity in a solution. The exchange of ions generates a voltage that is measured by the pH meter converting the voltage into a readable pH value. The glass electrode was invented by Nobel Prize winner Fritz Haber in 1909,
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