How to Accurately Test Pool Water

Regularly testing your pool water is a small investment to prevent large problems in a pool. Pool water testing 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 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.  

How often should I test my pool water? 

To maintain a pool that is sanitary, crystal clear, and balanced, you should be testing your pool’s chlorine and pH levels at least two to three times per week, and you should test the 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 throw a large pool party, check the water as soon as you can once the party ends. If your kids spend each summer day swimming in the pool, you will probably want to test it nearly every day. If a rainstorm rolls through, you may 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 is 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.

Most pool test strips also offer a range of testing options. The classic 5-in-1 test strip checks 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. A variety of strips on the market offer tests with a narrower focus. These include TDS strips, phosphate strips, salt strips, and copper strips. To keep a well-maintained pool, you must keep tabs on all these levels, though they require more infrequent testing. 

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 and 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 these devices are electronic meters you can dip into the pool. They provide read-outs of pH balance or TDS levels on their screens, while other devices install in the pool and 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 to use pool test strips

To achieve accurate results with your pool test strips: 

1. Immerse the strip in your pool water briefly. 2 seconds of immersion should be plenty.
2. Remove the strip with pads facing upward. Be sure not to shake off excess water.
3. Hold the strip still for 15 seconds.
4. Compare the strip to the legend on the bottle and match the colors to their corresponding values.
5. Balance your pool’s chemical levels accordingly.    

Advantages of pool test strips 

• This is one of their greatest advantages. Despite their low cost, test strips yield fairly accurate results.
• Simple to use. All you need is the pool, the strip, and the color-coded legend on the back of the bottle the strip came in. 

Disadvantages of pool test strips

• May need greater supply. Keep in mind that you will go through pool testing strips much quicker than you will 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.
• Can expire. If you have leftover strips from last summer, be sure they have not expired before dipping them in your pool. An expired test strip will not provide you with accurate readings of your pool. 

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 water samples, and liquid pool test kits can show faulty results if an incorrect amount of solution is added to the water during the test. In contrast, pool test strips require no technique and deliver the same accuracy of information. 

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How to use 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 shakethe 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 match 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; with other kits, you will see bright red water. Ensure you 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.

Advantages of pool test kits

• Easier to match colors. The colors on pool test kits are easier to distinguish than those on pool test strips.
• Supply lasts longer. Pool test kits are initially a more expensive investment than test strips, but the reagents will last the length of the summer without needing replacements. However, you should purchase new reagents at the start of each new pool season.
• More comprehensive. Most pool test kits offer a more comprehensive analysis of your pool’s chemistry. For experienced pool owners, this is a positive. Novice pool owners are better off sticking to the simplicity of test strips.

Disadvantages of pool test kits

• Less accurate results. 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.
• More time consuming. Using a pool test kit takes far longer and requires more focus than using test strips.

What levels should my pool chemistry be? 

How to test chlorine in a pool

Why is chlorine in my pool? 

Chlorine is the key factor in keeping your pool water clear and free from bacteria. 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 keeps 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.

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.

Why should I test my pool's chlorine levels? 

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

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 are allowed to bloom, they provide a home for bacteria to flourish and destroy pool cartridge filters. In addition to posing health risks to those swimming in your pool, algae growth turns 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 have ever swum in a heavily chlorinated pool, you are aware just how badly chlorine can make your eyes and nose sting. It can also fade bathing suits and strips oil from your skin, leaving it dried out and itchy.
• Waste: Your pool does not need this much chlorine to operate efficiently, so there is no reason to waste your chlorine tablets and money maintaining a pool with high chlorine content.   

How to raise chlorine in a pool

To raise your pool’s chlorine levels, you must 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” does not 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 to prevent the sun’s rays from burning off the chlorine you add. You should also wear goggles and protective clothing to protect yourself from the chemical.

When shocking your pool, calculate the amount of shock you 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.

How to lower chlorine in a pool

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 to wait it out. 

How to test a pool’s pH

What is the best pH for a pool? 

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 range from 7.4-7.6, just above the neutral value. 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 is worth noting that each number above or below 7 is a 10 times 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’s pH?

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

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 causes 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 corrodes all of your pool's metallic fixtures. This includes your ladders, the pool’s pump, and the diving board. Corrosion can shorten your pump’s lifespan, leading to premature pump failure. Acidic pool water can also fade swimwear, causing bathing suits to wear out quicker and become susceptible to bleaching. Water with a low pH destroys plaster in the pool, as well as stains 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.  

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

• Eye and skin irritation: Just like with pool water with a low 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 to raise pH in a pool

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

• Soda ash (sodium carbonate):  You need about 6 ounces of soda ash to raise the pH 0.2 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 need 12 ounces of soda ash. If your pool is 20,000 gallons, you must 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. 

How to lower pH in a pool

To decrease the pH of your pool, you 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 should avoid using it on a windy day. You do not want to risk this chemical 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 dissolves within 15 minutes. Wait around 6 hours, then test it to make sure you have 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 prevents the acid from 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 to add only ¾ of the recommended amount  to avoid overcorrecting. Once added, turn the pump back on and allow the acid to circulate. 

Muriatic acid is thought to be more effective than sodium bisulfate. However, if muriatic acid sits on the floor of your pool for too long, it can damage the material. 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. 

How to test a pool's alkalinity 

What is total alkalinity in a pool? 

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 can 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 will 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, and 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, floors, and around the 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 and 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 to raise pool 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, pool baking soda packaging comes 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. 

How to lower pool alkalinity

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

• Dry acid and muriatic acid: The primary difference between lowering alkalinity and lowering pH is the dosage added. You can find these instructions on the label, on an online pool calculator, or by 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 on 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.