How to Accurately Test Pool Water

Regularly testing pool water is a cost-efficient means to solve small imbalances before they become bank-breaking disasters. Testing your pool is also a proactive way to maintain the aesthetic appeal and lifespan of your pool. Left unattended, a slightly diminished pH level can result in a destroyed pool pump, corroded ladders, and pockmarked concrete infested with algae. Chlorine eradicates bacteria, protecting you and your guests from exposure to pool-borne illnesses. Vigilant testing, though perhaps tedious, arms you with knowledge and grants you the power to take corrective action before a fixable problem becomes an ongoing nightmare of expenses.  

1. How often should I test my pool water? ⌄

2. How do I test my pool water with pool test strips? ⌄

3. How do I test my pool water with a water test kit? ⌄

4. Testing for chlorine ⌄

5. Testing for pH ⌄

6. Testing for total alkalinity ⌄

How often should I test my pool water? 

To maintain a pool that is sanitary, crystal clear, and balanced, you should be testing your chlorine and pH at least two to three times per week. You should test your alkalinity once per week. Other measurements demand less frequent testing, but the more you test your pool the more opportunity you have to balance the water’s chemistry. 

Frequency of testing will also greatly depend on factors like pool usage and weather. If you’re throwing a large pool party, check the water after your guests have departed. If your kids are spending each summer day swimming in the pool, you’ll probably want to test it nearly every day. If a rainstorm rolls through, you’ll want to check to see if the precipitation disrupted the pH balance or chlorine levels. Chlorine is vital in protecting your pool from harmful bacteria and algae growth, so it is important to monitor it diligently. 

Here’s a guide indicating the frequency with which you should be monitoring your pool’s levels: 

How do I test my pool water? 

Pool test strips 

Conventionally, pool test strips have been the most popular testing option for homeowners with pools. They are simple, inexpensive, and provide quick results on the standard pool test of chlorine, pH, and total alkalinity. There are also a host of other pool testing strips to determine levels of potential contaminants like TDS, salt, bacteria, and phosphates.  

Pool test kits 

You can also test your pool’s chlorination, pH, and total alkalinity with water test kits. Known by popular brand-names like Taylor or Poolmaster, pool test kits use liquid reagents to test your pool’s chemistry. These reagents alter the color of a pool water sample to indicate the levels of chlorine, alkalinity, and pH. These are more labor-intensive than test strips and come with a bit of a learning curve.      

Digital & electronic testers 

Electronic pool testers and digital test kits have increased in popularity, as they can deliver comprehensive pool water analyses straight to your smartphone. Some of them are electronic meters you can dip into the pool. They will then provide read-outs of pH balance or TDS levels on their screens. Others are devices installed in the pool that connect to an app on your smartphone. These can deliver you detailed read-outs of your pool’s levels throughout the day. Unfortunately, some electronic and digital tests have dubious accuracy and tend to be the more expensive pool-testing options.

How do I test my pool with pool test strips?

To achieve accurate results with your pool test strips: 

1. Immerse the strip in your pool water briefly (2 seconds will suffice).
2. Remove the strip with pads facing upwards (be sure not to shake off excess water).
3. Hold the strip still for 15 seconds.
4. Compare the strip to the legend and match the colors to their corresponding values.
5. Balance your pool’s chemical levels accordingly.    

What are the advantages of pool test strips? 

Pool test strips are inexpensive, which is one of their greatest advantages. Their low price point is not an indicator of lower quality readings either. They have the added advantage of being the most simple form of pool testing. All you need is the pool, the strip, and the color-coded legend on the back of the bottle the strip came in. 

However, you’ll need to keep in mind that you will go through pool testing strips much quicker than you will go through the materials of your liquid test. Most pool test strips come in bottles of 50, so depending on your frequency of testing you may need a couple of packs to make it through the summer. It’s also of great importance to check the expiration date on pool test strips. If you have leftover strips from last summer, be sure they haven’t expired before dipping them in your pool. An expired test strip will not provide you with accurate readings of your pool. 

Most pool test strips also offer a range of testing options. The classic 5-in-1 test strip will check the levels for chlorine, free chlorine/bromine, pH balance, total alkalinity, and total hardness. 6-in-1 test strips add a cyanuric acid test to that list. There is an assortment of strips on the market offering tests with a narrower focus. These include TDS strips, phosphate strips, salt strips, and copper strips. To keep a well-maintained pool you will need to keep tabs on all these levels, though they require more infrequent testing. 

Are pool test strips accurate? 

Pool test strips provide accurate readings of your pool’s chemistry. In fact, pool test strips are a more reliable method of testing your pool water than a liquid test kit. Pool test strips eliminate the risk of human error. Precision is key when adding reagents and measuring out water samples and pool test kits can show faulty results if an incorrect amount of solution was added to the water during the test. In contrast, pool test strips require no technique and deliver the same accuracy of information. 

How do I test my pool with a pool test kit? 

Pool test kits are significantly more involved than a simple strip. The basic chlorine, pH, and alkalinity test occurs in two stages and requires numerous reagents. 

To test for chlorine and pH with a kit:

1. Dip your arm elbow-length into your pool and gather a sample. This should be about 18 inches beneath the pool’s surface. The water chemistry of the surface may not be an accurate reflection of the entire pool. 
2. Make sure the water does not pass the fill line marked on the sides of the vials. The smaller vial tests the chlorine and the larger vial tests the pH. 
3. Add the designated drops of the OTO chlorine indicator reagent to the chlorine vial. Some kits use a powder to test chlorine levels. 
4. Add the designated drops of the phenol red reagent to the pH side. Many kits will also have you add one drop of chlorine neutralizer to the pH test to prevent the chlorine from interfering with the pH results. 
5. Place the caps on the vials and gently shake the water. You can achieve this by turning the kit upside down a few times. A vigorous shake can produce air bubbles and affect the color. Never use your fingers or hands to cover the vials. The oils and acids on your skin can change the pH readings. 
6. Match the color of the water to the color chart. The more yellow the water, the higher the chlorine levels. The redder the water, the higher the pH. Make sure you are matching the colors against a white background to ensure accurate results. 

To test for total alkalinity with a kit:

1. Gather your sample from the pool. Remember, it should be elbow-length deep and toward the middle of the pool. 
2. Make sure the water has reached the appropriate alkalinity line. This line is usually found about halfway down the pH vial. Some test kits will provide you with a separate vial to test alkalinity. 
3. Add the designated drops of the two indicator agents. This will turn the water a bright color like green or purple. 
4. Add one drop of sulfuric acid reagent and swirl the water. Continue to add one drop at a time, swirling after each drop. Count the number of drops it takes for the water to completely change colors. With some kits, this results in clear water, other kits this results in bright red water. You will want to check the kit’s instructions to know what color change you are looking for. 
5. Multiply the number of drops it took to alter the water’s color by 10. This will give the total alkalinity in ppm (parts-per-million). For example, if it took 8 drops to change the water’s color, your total alkalinity is 80ppm. 

What are the advantages of pool test kits? 

Many people believe that pool test kits produce more accurate results than pool test strips. This is not necessarily true. Pool test kits can produce skewed readings if the tester accidentally adds an extra drop of a reagent or shakes the vial too vigorously. If performed with care, the test kit’s results will give you clear readings on your pool water. The colored water is easier to visually match with the legend than the small colored patches on the test strips. However, testing with a kit will consume much more of your time and requires dedicated focus. 

Pool test kits are initially a more expensive investment, but the reagents will last the length of the summer without needing replacements. Though reagents have a long shelf life, it is recommended that you purchase new reagents at the start of each new pool season. Pool test kits that offer more expansive testing options, like total hardness or cyanuric acid, are considerably more expensive than strips with the same capacity.  If you prefer to test your pool with a test kit and are familiar with all the steps involved, it is an effective way to examine your pool’s chemistry. If you are a pool testing novice, pool test strips are probably the smarter choice. 

What levels should my pool chemistry be? 

Testing for Chlorine 

Why is there chlorine in my pool? 

Chlorine is the key factor in keeping your pool free from bacteria and crystal clear. Chlorine sanitizes pool water by a process called oxidation. When chlorine is added to water, it forms a weak acid called hypochlorous acid. This acid has a neutral electrical charge. Hypochlorous acid can penetrate the negative charge of bacteria’s cell walls and destroy the microorganism from the inside out. Chlorine’s remarkable disinfection properties will keep your pool clear of algae infestations and pathogenic bacteria. This protects your swimmers from pool-borne illnesses. Chlorine also oxidizes the organic material that is deposited in your pool by both swimmers and nature. This is what gives a well-maintained pool that beautiful shimmer. 

Why should I test my pool for chlorine? 

Chlorine can only keep your pool pristine if it’s consistently being replenished. When chlorine breaks down organic matter or bacteria via oxidation, the chlorine molecule itself is also degraded. The sun’s ultraviolet rays also break down chlorine. Chlorine is your pool’s most important line of defense against contamination, so it’s necessary to regularly monitor its levels.

What is the difference between total chlorine and free chlorine? 

You’ve probably noticed your test strips show two readings for chlorine: total chlorine and free chlorine. Total chlorine is the measurement of the total amount of chlorine present in your water. Free chlorine measures the amount of unused or available chlorine in the water. The free chlorine still can disinfect bacteria and algae in the water. Free chlorine is the reading you should be primarily focused on.   

What happens if my pool doesn’t have enough chlorine? (below 1 ppm)

• Contamination: Without chlorine to break down contaminants, potentially dangerous bacteria, algae, and microorganisms will run rampant in your water. When algae is allowed to bloom, it provides a home for bacteria to flourish in. Algae will destroy your pool cartridge filters. In addition to posing health risks to those swimming in your pool, algae growth will turn the pool water green and cloudy.
• Pool imbalance: Chlorine, pH, and alkalinity work in tandem to stabilize your pool’s water. When the chlorine levels are too low, you will have great difficulty keeping your pH and total alkalinity in check. 

What happens if my pool has too much chlorine? (above 4 ppm)

• Eye & skin irritation: If you’ve ever swum in a heavily chlorinated pool, you’re aware just how badly chlorine can make your eyes and nose sting. It also strips oil from your skin, leaving it dried out. Chlorine also has bleaching properties and can fade your bathing suits.
• Waste: Your pool doesn’t need this much chlorine to operate efficiently, so there’s no reason to waste your chlorine tablets and money maintaining a pool with high chlorine content.   

How do I balance my pool’s chlorine levels?

Raising chlorine levels 

To raise your pools chlorine levels, you will need to introduce more chlorine into your pool. This can be done by adding chlorine tablets or “shocking” your pool with granular chlorine. 

• Chlorine tablets: Add chlorine tablets to your chlorinator, skimmer basket, or floating chlorine dispenser. These will dissolve slowly in the water and introduce new chlorine into the water to fend off bacteria. If you do not have an automatic chlorinator in your pool, you will need to manually add chlorine tablets yourself every week. 
• Shock your pool: That strong, distinctive “pool smell” doesn’t actually come from chlorine. It comes from chloramines, a byproduct of chlorine created during the disinfection process. Shocking your pool dramatically raises the chlorine level for a brief time, both to destroy these chloramines and to stabilize your pool’s chlorine levels. Be sure to only shock your pool after dusk, as the sun’s rays will burn off chlorine. It is also important to wear goggles and protective clothing to protect yourself from the chemical 

When shocking your pool, calculate the amount of shock you will need according to the manufacturer’s instructions. Most pool shocks need to be pre-dissolved in warm water before they can be added to the pool. After dissolving, walk around the perimeter of the pool, slowly pouring the shock in to ensure an even distribution. Wait at least eight hours before swimming in the pool again.

Lowering chlorine levels      

Reducing chlorine levels in your swimming pool is very simple. 

• Stop adding chlorine and wait: Continued exposure to sunlight, swimmers, and dirt and debris will reduce the chlorine levels in just a day. Chlorine is perpetually being depleted by the pool, so if your levels are running a little high, your best and safest bet is just to wait it out. 

Testing for pH

What is my pool’s pH level? 

Your pool’s pH level is the measurement of the total acidity and alkalinity balance of the water. The pH scale runs from 0 to 14, with 7 in the center representing neutral. A pH level of 7 is neither acidic nor basic. Pools strive to maintain a pH level just above this neutral value, from 7.4-7.6. The pH of the human body itself falls in the neutral range, and the ideal pool pH approximately matches the relative neutrality of human eyes and mucous membranes. It’s worth noting that each number above or below 7 is actually a 10x increase in acidity or alkalinity. For example, a pH score of 4.0 is ten times more acidic than a pH score of 5.0. Similarly, a pH score of 9.0 is ten times more alkaline than a pH score of 8.0.

Why should I test my pool for pH?

The chemical imbalance that arises from improper pH levels can leave your pool walls stained, your water discolored, your pump corroded, and irritate your skin, eyes, and nose. 

What happens if my water is too acidic (below 7.4 pH)?

• Eye and skin irritation: Water with a low pH causes a stinging, burning sensation in the eyes and nasal cavities of swimmers. Acidic water irritates the skin as well, causing it to itch, burn and feel dry. This is because water with high acidity strips the skin of oils your body naturally produces. 

• Damaged concrete and vinyl: Water with a low pH level will cause concrete surfaces to become pitted, providing algae a perfect place to hide away and bloom. Low pH can cause etching on metal, concrete, and plaster walls. It can roughen mosaic tiles and diminish their aesthetic appeal. Acidity also causes vinyl panels to lose their elasticity, making them wrinkle, buckle, and eventually tear. 

• Corrosion: Acidic water will corrode all of your pool's metallic fixtures. This includes your ladders, the pool’s pump, and the diving board. Corrosion will shorten your pump’s lifespan, leading to premature pump failure. Acidic pool water will also fade swimwear, causing bathing suits to wear out quicker and become susceptible to bleaching. Water with a low pH will destroy any plaster in the pool, as well as stain the walls of the pool. 

What happens if my water is too alkaline (above 7.6 pH)

• Scale build-up: When the pH is too high for an extended period, scale can form across the surface of the pool floor, the walls of the pool, and the pipes. The pool’s waterline will gather debris and darken the pool walls. Scale will also attach itself to media filters, like sand, reducing their filtration efficiency and permitting dirt and contaminants into your water. Circulation will also decrease as the pipes become clogged with scale.  

• Reduces chlorine’s effectiveness: The efficacy of chlorine is drastically reduced in water with a high pH level. This will allow algal buildup as well as give your pool a murky, hazy coloration. Chlorine will no longer be able to break bacteria down with the same ease. You also waste a lot of chlorine if you attempt to balance highly alkaline pool water’s chlorine levels. 

• Eye and skin irritation: Just like with pool water too low in pH, you will experience physical discomfort swimming in pool water high in alkalinity. The body prefers to be in a neutral pH environment that mirrors its own balance, and high pH pool water will leave your eyes and nose burning and your skin feeling dried out and sticky. 

How do I balance my pool’s pH level? 

To adjust your pool’s pH level, you need to add in a chemical agent to either raise or lower the balance.

Raising pH levels 

To raise the pH level of your pool, you will need sodium carbonate, more commonly called soda ash. These are commonly sold under names like “pH Increaser” or “pH Plus”.

• Soda ash (sodium carbonate):  You’ll need about 6 ounces of soda ash to raise the pH 0.2 pH points in a 10,000-gallon pool. So, for example, if your pool is 10,000 gallons, and you need to raise the pH from 7.0 to 7.4, you’ll need 12 ounces of soda ash. If your pool is 20,000 gallons, you’d need to add 24 ounces to raise the pH from 7.0 to 7.4. After you’ve measured out the appropriate amount of soda ash, mix it in a bucket of water before adding it to your pool. Soda ash will not dissolve evenly if dumped directly into the pool. After you’ve mixed your solution, walk around the perimeter of the pool and pour the soda ash into the water. Wait one hour and allow the pool pump to circulate the soda ash before checking the levels. Soda ash may turn your pool water a hazy color but it will clear up within a day. 

Lowering pH levels

To decrease the pH of your pool, you will need either sodium bisulfate (dry acid) or muriatic acid. These are commonly sold as “pH Minus” or “pH Reducer”. 

• Sodium bisulfate (dry acid): Sodium bisulfate comes in the form of dry powder, so you’ll want to avoid using it on a windy day. This is a chemical and you do not want to risk it blowing onto your skin and eyes or all over your patio. Pour the powder into the return jets sites, so the water can circulate the dry acid throughout the pool. Only add ¾ of the recommended amount. You want to avoid accidentally lowering the pH too much, and you can always add more later. The dry acid will dissolve within 15 minutes. Wait around 6 hours, then test it to make sure you’ve achieved your desired results. 
• Muriatic acid: Muriatic acid is a much more potent chemical than sodium bisulfate. You want to take extreme caution when using it to balance your pH (keep in mind, this is a chemical used to pickle steel and dissolve rocks). It will burn both your skin and the concrete around your pool. Wear goggles and protective clothing and make sure none of it spills onto your tiles, masonry, or metal fixtures like ladders. Turn off the pool pump and let the water become still. This step is to avoid the acid merely resting on the pool’s surface. After about an hour, pour a direct stream of muriatic acid into the deep end of the pool, avoiding all metal and concrete surfaces. (Remember, only add ¾ of the recommended amount. You want to avoid overcorrecting.) You then turn the pool back on and allow the acid to circulate. 

This method is thought to be more effective, however, if muriatic acid sits on the floor of your pool for too long, it can damage the pool floor. To avoid this, you can leave the pool running and slowly pour it in by the return jets, thus allowing the pool to circulate the acid. Either way, you’ll want to wait 4-6 hours after you’ve added the acid before returning to test the pool water. 

Testing for total alkalinity 

What is my pool’s total alkalinity? 

Your pool’s total alkalinity is a measurement of the water’s capacity to resist sudden changes in pH. Total alkalinity is your pool’s pH buffer. By neutralizing acids in the water, the total alkalinity is able to stabilize the pH level and prevent it from fluctuating. Though it sounds like it’s the same measurement as your pH’s alkalinity, your total alkalinity is a different metric. pH is measured against a scale. Total alkalinity is measured in density (parts-per-million, or ppm). It is the number of total dissolved alkaline particles in your pool water. To establish a proper buffer for your pH balance, you’ll want to maintain a total alkalinity between 80-120ppm. If both your pH and your total alkalinity are imbalanced, you should adjust your alkalinity levels first. 

Why should I test my pool’s total alkalinity? 

Haphazard pH levels can cause detrimental damage to your pool itself. Steadying askew pH levels can be one of the most frustrating tasks in pool maintenance. It is very easy to overcorrect when adjusting pH levels and you want to avoid rapidly cycling back and forth between basic and acidic pool water. Maintaining a balanced total alkalinity level gives you some assurance that your pH level is protected against drastic changes. 

What happens if my total alkalinity is too low? (below 80 ppm)

• pH bounce: When total alkalinity is low, the pH level can fluctuate wildly between acidic and basic. If you were to add in large quantities of an agent like soda ash to try and raise a low pH level, you could end up far overshooting your target and driving the water too high into the alkaline range. When the total alkalinity is too low, pH cycles back and forth uncontrollably. 

• Staining, etching, & corrosion: Just like when the pH is too low, low total alkalinity causes damage to your masonry, tile work, mosaics, and vinyl. Grooves can form in your pool walls as the material degrades. Metal fixtures will rust and corrode. Vinyl walls will stain. Virtually everything housing your pool and in your pool is at risk of degradation when exposed to low total alkalinity for extended periods of time. 

What happens if my total alkalinity is too high? (above 125 ppm)

• Scale: When the alkalinity is too high, calcium carbonate deposits can build up on your pool walls and floors as well as around your pool’s pump. These deposits, known as scale, can cause permanent structural and aesthetic damage to your pool. Scale can also clog your pool filters and render them ineffective, forcing you to replace them prematurely. 

• Pump & pipe damage: When scale builds up in your pipes and around your pump, their performance is significantly diminished. As your pump clogs with scale, it will no longer circulate water as quickly or effectively. Damaged pool filters will not be able to remove contaminants or algae with the same proficiency. Your pool water’s safety can become compromised. 

How do I balance my pool’s total alkalinity? 

Balancing total alkalinity is a similar process to balancing the pool’s pH. In the process of balancing your pool’s total alkalinity, it’s very possible you will upset the pool’s pH levels. However, keep in mind, balanced total alkalinity promotes balanced pH. Once your total alkalinity levels are in check, slowly make adjustments to bring the pH into the desired range.  

Raising total alkalinity 

The cheapest and most popular way to raise your pool’s total alkalinity is with sodium bicarbonate, known widely as baking soda. 

• Baking soda: The baking soda you purchase at your pool store or online is no different in composition from the baking soda you purchase at the grocery store. However, the pool store’s packaging will come with dosage instructions, making it the wiser option. If you are ever unsure of the amount of any balancing agent to add, you can consult an online pool calculator. Baking soda is a powder, so avoid adding it on windy days. Add the baking soda into the pool in an arcing pour to avoid it collecting too densely in select places. Once you’ve added the appropriate amount, wait six hours before re-testing alkalinity and pH. 

Lowering total alkalinity 

Just like with lowering pH, you lower your pool’s total alkalinity with dry acid or muriatic acid. 

• Dry acid & muriatic acid: The primary difference between lowering alkalinity and lowering pH will be the dosage added. You can find these instructions on the label, or again, by using an online pool calculator or consulting your pool store. The amount of acid required to lower alkalinity is usually greater than the amount required to lower pH, so expect your pH to drop below the optimal range. Remember, always add in less than the recommended dosage. It is better to slowly adjust your water’s levels than get trapped in a cycle of overcorrection. After your total alkalinity is in range, wait to see if the pH balance corrects of its own accord. You can aid this process by aerating your pool. Set your pool pump to the highest setting and point your return jets upward. Wait and continue to test your pool’s chemistry. If after a few days your pH still needs a nudge, add in light amounts of soda ash. 

| For more on pool maintenance, explore our blog on how to maintain your pool filter cartridge. |