Dr. Pool’s Guide to Water Testing


Hello again, It’s Dr. Pool – coming to you from the Lab here at In The Swim.

Today’s topic is Pool Chemistry – how to sample, test, evaluate and adjust your pool water chemistry.

Whether you have a small pop-up pool, or a small waterpark in your backyard, the process is the same.

Why Test Your Pool Water?

Water Balance can change rapidly, from active pool use or from all matter of windblown debris and precipitation.

Having “Balanced Water ” means that your levels of Alkalinity, pH, Calcium Hardness and Stabilizer are proper – which protects your equipment, but also your swimmers, by allowing your sanitizer to work most effectively.

The only way to know what these 4 levels are, is to test your pool water – frequently. Accurate pool testing also allows you to make correct adjustments to these water balance parameters.

Testing for sanitizer levels is even more crucial for the safety of your swimmers, and to make sure that you’re not using too much, or too little chlorine in your pool. You can also determine when to shock the pool, by testing for both Free and Total Chlorine levels.

Pool Water Tests

Sanitizer levels in your poolChlorine, Bromine or Splashes – your sanitizer is the fastest changing parameter; it depletes rapidly in the water. Test your levels daily until you determine the proper amount to add – too little and bacteria and algae will grow, and too much and you risk chloramine formation and pool surface deterioration.

Chlorine tablets are an expense that can be reduced, by using only as much as you need. Even with Salt Generators, running a level no higher than 1.0 ppm will reduce the workload of your salt cell, and result in more comfortable swimmers.

pool pH testsThe next fastest changing measurement is pH. Everything on Earth has a pH value, I’m sure you’ve heard of “pH balanced” shampoo, and you probably know that pH is a scale of relative basicity or acidity, ranging from 0 – 14, with 7.0 being neutral, or neither basic or acidic.

Swimming pools pH levels are best in the 7.2 – 7.4 range. Your chlorine will be most effective at a lower pH range, and your pool surfaces will be safe from scaling. Allow your pH to drop below 7.0 however, and your water can become corrosive towards your pool surfaces and equipment.

alkalinityThere is an expression of “Alkalinity First” – referring to the importance of adjusting your Alkalinity, before adjusting pH or other water balance parameters. It’s listed here third however, due to it’s speed of movement, relative to the other 4 water balance measurements.

Alkalinity is a measurement of the carbonates and bicarbonates in the water, and is sometimes defined as the “buffering capacity” of your pool water. Test your Alkalinity at least weekly, to prevent it drifting up or down; out of range of 80-120 ppm. Keeping your Alkalinity in check will help keep your pH in check, which in turn, helps keep your sanitizer in check.

hardnessThis is the measure of the hardness or softness of your pool water. You’ve heard of water being soft or hard. Hard water has high levels of Calcium dissolved in the water, and soft water has less.

Testing for Calcium Hardness checks for levels of Calcium in the water. Too little and the water may become aggressive, and seek to pull Calcium from the pool surfaces. Too much Calcium, and deposits may form, or you may have frequent issues with cloudy water.

Pools should maintain Calcium levels in the 180 – 220 ppm range to be considered “balanced”, although it can usually climb up to 400 ppm with little adverse effects.

stabilizerAlso known as “Conditioner”, Stabilizer is known chemically as Cyanuric Acid, which was found 40 years ago, quite by accident, to protect the chlorine molecule from the sun.

We put Cyanuric Acid into our chlorine tablets, but most pool owners need to add additional Stabilizer to the water, to build the residual, or level to 40-80 ppm.

Stabilizer is the slowest to change – of all of these pool levels. It only depletes through dilution; that is, from backwash, splash out, lowering the water for winter or if you drain and refill the pool.

How to Test Your Pool Water

3 methods of Pool Testing: Test Strips, Test Kits and Digital Testers.

Test Stripsaquachek-test-strips. These are considered the least accurate, but also the most convenient to use. I’d rather see our customers use a liquid test kit (below), for more accurate measurements, but I understand if you don’t share my passion for titration testing. At least the water is being tested!

Just dip the strip and compare to the color chart on the bottle. Use a test strip that will test all of the 5 water balance parameters, listed above. The 7-way Test Strip is the most complete pool strip. We also have test strips that measure for copper, borates, phosphates, salt and biguanide levels.

Test Kits. With this type of testing, there are certainly more steps involved, and each test is performed individually. Fill the vials with a test sample, and add the colored indicator reagents to compare sample colors for pH and Chlorine.k2005-test-kit

Alkalinity and Hardness are measured using a titration test. After adding the indicator solution, you add a titrant, dropwise, until a complete color change is observed. Multiply the number of drops by 10 (t x 10) to determine the readings.

Stabilizer tests are performed with a turbidity test. The reagent, mixed with a pool water sample, will turn cloudy in the presence of Cyanuric Acid. Squirt the mixture into the vial with the black dot at the bottom. Stop filling the vial when the dot disappears, or is no longer visible. Read the measurement on the vial, at the point of the water level.

The advantage of Test Kits are more accurate results, for more accurate adjustments. Using a test kit like the Taylor K-2005 will perform all pool water balance tests perfectly. The Taylor FAS-DPD test kit also tests all 5 parameters, but uses a titration sanitizer test, for more accurate results.

Digital Testers. There are two types of Digital Pool Testers – Test Kits that read test vials with photometric scanners, or Handheld Testers, that you dip into the pool directly to sample the water.

The advantage of digital measurement is clear – more accurate results! In addition, many digital testers can display the amount needed for adjustment, so chemical dosage charts are not needed.colorq 7 test kit

ColorQ PRO 7 test kits, preferred by pool pros and water treatment professionals, uses a digital photometer, and provides a display of test results and adjustment chemicals needed.

Highly accurate photometric scanner precisely determines all water balance tests, over a wider range than most other test kits. Insert the test vial into the photometer, and push one button to obtain test results and recommendations.

Hand Held testers have been around for many years. We carry many different models, such as the LaMotte PockeTesters, shown below left, Individual testers for either: pH, Salt, TDS or ORP. The SafeDip tester will test for pH, Chlorine, Salt or TDS, and the new, slim UltraPen has a version for pH testing, and one for ORP (Oxidation Reduction Potential). Guess which UltraPen is which, based on their red or yellow color? 🙂handheld-digital-pool-testers

Where to Test Your Pool Water?

Whether you use test strips, fill a test vial, or use a digital test device, take your water test sample at a water depth of 4-6″, so that you are not testing surface water.

Also, take your water sample from an area of good circulation, just downstream from one of your return inlets.

When to Test Your Pool Water?

The best method is to test your water daily, until you can establish correct dosing for the pool. After you have achieved solid water balance that lasts longer than a few days, you can reduce your testing to several times per week.

Now that we’ve covered the Why, What, How, Where and When of pool water testing, the only question left is Who… will test the pool water?

If you are the official pool tester, enjoy the excitement that is Chemical Testing and Analysis!

Dr. Pool

Dr. Pool


Dr. Pool’s Guide to Water Testing — 4 Comments

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