How to Properly Maintain Swimming Pool Water Chemistry

Maintaining the chemistry of your swimming pool will prevent harmful bacteria from building up and keep the pool pleasant and safe for your friends and family to use. Doing this yourself instead of hiring a professional can save you money. Perform regular maintenance to keep the pool clean and ensure the alkalinity, pH, free chlorine, and cyanuric acid are within the acceptable levels.

Method 1

Method 1 of 3:

Doing General Maintenance

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1
Test the pool water before and after making chemical adjustments. Pick up several pool testing kits from a pool supply store or order them online. Plan to test the pool water twice a week whether it’s been used or not. Also, always test the water after changing any element of the water chemistry to ensure the pool is safe to use. Follow the directions on your kit to measure the alkalinity, pH, free chlorine, and cyanuric acid levels in the water.^{[1]XTrustworthy SourceCenters for Disease Control and PreventionMain public health institute for the US, run by the Dept. of Health and Human ServicesGo to source}
- Typically, you’ll fill containers with pool water and add the specified number of drops of bleach or other chemicals to the samples. Then, dip a test strip into each container following the manufacturer’s instructions to evaluate the water’s chemistry.
- You can get free test strips online by visiting the Water Quality and Health Council website at https://waterandhealth.org/healthy-pools/.
2
Run the pool pump at all times if possible. Properly circulating the water is essential for maintaining the chemistry in your pool. Let the pump run continuously so the water stays clean and chemicals like chlorine are evenly dispersed. If you can’t keep the pump on all the time, run it at least 10 hours per day.^{[2]XResearch source}
- Be sure to backwash your filter regularly so the contaminants travel out of your pool and into the waste port.
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3
Clean your pool at least once per week. Regularly cleaning your pool helps to remove contaminants like skin, oils, sunscreen, and hair products that disrupt the chemistry of the water. Use a net skimmer to remove bugs, leaves, and other surface debris. Vacuum the pool walls and floor to remove sunken debris and get a deeper clean. Clean the walls and floor of your pool with a pool brush to remove mildew and mineral buildup.^{[3]XResearch source}
- Work from the shallow end to the deep end and be sure to clean and empty all the filters when you’re done.
- To maintain the pool, get a vacuum once a week. The plaster and pebbles cannot tolerate loads of dust.^{[4]XResearch source}
- It does wonders for the color of the pool. When you go on a vacation and come back, the color of the water may be Tahoe blue or have a grayish tint. But when you turn on the vacuum, you can see streaks, and the pool becomes blue again.^{[5]XResearch source}
- It is not expensive. Most vacuums cost less than $200.
4
Shock the pool once every week at night. To shock the pool, add 3 lb (1.4 kg) of calcium hypochlorite shock. As chlorine works to clean your pool, it binds to other chemicals like ammonia and nitrogen, which not only render it effectively inactive but also create an irritant that can cause skin conditions like jock itch. To eliminate combined chlorine, shock your pool on a regular basis.^{[6]XResearch source}
- Shock your pool after rainstorms and pool parties as well to sanitize the water.

Method 2

Method 2 of 3:

Adjusting the Alkalinity and pH

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Alkalinity buffers the pH and can prevent large increases or decreases in the acidity and basicity of the water. Test and adjust the alkalinity before adjusting the pH. If the alkalinity is too low, mix baking soda with water and pour the mixture into the pool to increase it. If the alkalinity is too high, adjust it along with the pH using muriatic acid.
Tip: Add 1.5 pounds (0.68 kg) of baking soda to a 10,000 US gal (38,000 L) to raise the alkalinity 10 ppm.
2
Maintain a pH level between 7.2 and 7.8. The term pH refers to how acidic or basic your pool water is. Typically, the tap water you use to fill your pool has a neutral pH of 7, but additives or contaminants can change the pH. A pH of 7.2-7.8 is the ideal range for pool water, so if your reading is above or below these levels, it's important to adjust it. Having the right pH ensures the water won't irritate your skin or eyes and will also keep the water clear.^{[7]XTrustworthy SourceCenters for Disease Control and PreventionMain public health institute for the US, run by the Dept. of Health and Human ServicesGo to source}
- If swimmers are having a problem with “burning eyes,” the pH is probably to blame, not the chlorine.
- Pool owners with zero CYA will notice that the chlorine is more effective at a low pH (around 7.2) while owners who have CYA in their water will see similar kill times even at a high pH.
Lower the pool’s pH levels using muriatic acid. Find muriatic acid (AKA hydrochloric acid) at a pool supply store. Read the packaging to determine how much to add to your pool to lower the pH to an acceptable level. Pour the muriatic acid directly into the deep end of the pool while the pool pump is on and the water is circulating. Retest the water after about 6 hours of continuous filtration and readjust the pH as needed. This will prevent “bouncing,” which occurs when the pH levels switch between being high and low.
Warning: Wear long-sleeved clothing, pants, close-toed shoes, gloves, goggles, and a respirator or mask when working with muriatic acid to prevent irritation to your skin, eyes, or lungs.
Increase the pH with soda ash. Soda ash (AKA sodium carbonate) can easily raise the pH and total alkalinity of your pool water. In general, plan to use 6 ounces (170 g) of soda ash per 10,000 gallons (38,000 L) to raise the pH by 0.2. Pour the soda ash into a clean bucket then fill the bucket with water and mix the soda ash into it. Then, spread the mixture around the perimeter of the pool. Ensure the pump is on so the soda ash dissolves and gets evenly distributed.

Method 3

Method 3 of 3:

Sanitizing Your Pool

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Chlorine is measured in parts per million, or ppm. If the levels are lower than 1 ppm, there may be harmful bacteria lurking in the water. Conversely, if the chlorine levels are too high, you might experience skin and eye irritation.^{[8]XResearch source}
Variation: Chlorine is the most widely used pool sanitizer, but there are other options available, including bromine and ozone as well as sanitizing systems such as ionization and ultraviolet irradiation.
2
Use chlorine tablets to easily increase the amount of chlorine in the pool. It's much less work to use chlorine tablets or sticks rather than granular chlorine, which has to be pre-dissolved in water and added on a daily basis. The most common and least expensive form of chlorine is 3 in (7.6 cm) tablets, which are slow-dissolving and require less maintenance. If you have an above-ground pool, a small in-ground swimming pool, a hot tub, or a spa, 1 in (2.5 cm) chlorine tablets are ideal.^{[9]XResearch source}
- The active ingredient in chlorine tablets and sticks is called “Trichlor” (or Trichloro-S-Triazinetrione), and the active ingredient in granular chlorine is called “Dichlor” (or Sodium Dichloro-S-Triazinetrione).^{[10]XResearch source}
- Look for a concentration of 90% Trichloro-S-Triazinetrione in chlorine tablets or sticks.^{[11]XResearch source}
- If you choose to use granular chlorine, look for a concentration of 56% to 62% Sodium Dichloro-S-Triazinetrione in granular chlorine.
3
Put the chlorine tablets in a floating chlorine feeder. Read the packaging on the tablets to find out how many to use based on the existing chlorine levels in the water and the size of your pool. Put the tablets in a floating chlorine feeder and put the feeder in the pool. As the feeder floats around, the chlorine will gradually dissolve and be distributed throughout the pool water.^{[12]XResearch source}
- Instead of a floating feeder, some pools have a skimmer basket that hooks on the side of the pool. If your pool has this, drop the chlorine tablet right into the basket. Skimmer baskets are commonly used with above-ground pools.
- Other pools come equipped with chemical feeders. Chemical feeders slowly meter out precise amounts of chlorine into your pool water automatically and offer very precise control over the amount of chlorine being added to the swimming pool. If a feeder is adjusted properly, you may not have to worry about your chlorine level for a week or more.
If you add too much chlorine or shock to your pool, you can easily lower it with a chlorine neutralizer, available at pool supply stores. Follow the instructions on the package to find out how much to add based on the size of your pool and how high the chlorine levels are. Then, pour the liquid into the pool while the pump is on and let it disperse.
Variation: The sun naturally breaks down chlorine, so if the chlorine levels are less than 5 ppm, simply stay out of the pool for a few days and let the sun do its job. Or, you can drain some water and replace it with fresh water to dilute the pool. Just be sure to do a water test before swimming to ensure the chemicals are within acceptable levels.
5
Maintain cyanuric acid levels at no higher than 40 ppm. Cyanuric acid (CYA, also called isocyanuric acid) must be used in outdoor pools to keep the sun from burning off the chlorine. It’s included in the majority of commercial dichlor/trichlor tablets. Although cyanuric acid is a stabilizing ingredient in chlorine that prevents it from being destroyed by the sun, it does so at the cost of reducing the effectiveness of the chlorine. Test the water regularly to check the CYA levels and ensure that the chlorine won't lose its sanitizing ability.
- At 40 ppm, cyanuric acid will allow chlorine to perform optimally (high levels of CYA contribute to Total Dissolved Solids (TDS) which interferes with chlorine activity).^{[13]XResearch source}
- If the CYA is too high, switch to chlorine tablets or sticks that don't contain it until the levels drop an acceptable amount.

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What is hard water?
Community Answer
Hard water is water rich in calcium deposits.
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How can I tell if the alkalinity is too high or too low?
Brianne Babbitt
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Test it. Have your local pool supply store test your water and get a test kit. There is no way to look at your water and know if the chemicals are out of balance. Even algae isn't always a balance problem.
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What do I add to pool water if the chlorine levels are above normal?
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Drain some water from your pool and replace it with clean, fresh water. Or you can add a chemical called Thio-Trine.
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In addition to its many other benefits, chlorine is also an effective algaecide and will keep algae from building up underwater in your pool.^{[14]XResearch source}
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Warnings

Add chlorine to water and not water to chlorine, as it may cause a violent reaction.
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These chemicals are hazardous. Keep out of reach of children.
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Always follow product label instructions from the manufacturer.
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Always wait a minimum of 2 hours between adding different chemicals to the pool to prevent any negative chemical reaction and to maximize the effect of your chemicals.
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Muriatic acid is the best choice for lowering pH levels, but creates dangerous fumes and should be used with extreme care.
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