How to Test Your Swimming Pool Water

©Eveniya Sheydt / Adobe Stock
A pool water testing strip

Common questions among new pool owners are about how often to test pool water. On average, pool owners get into the habit of testing their water once a week, and that’s the maximum amount of time I recommend waiting between tests. If you go longer than that, things can sometimes get away from you without you even noticing! Checking your pool’s water weekly helps you develop a consistent schedule for both chemical and equipment maintenance.

How to test pool water

The most common kinds of testing kits are testing strips, drop test kits, and digital test kits. Find one that fits your personal preferences, and testing your pool will be a breeze.

All testing kits, whether strips or drops, have an expiration date, and they become less accurate the closer you get to that date. For test strips, they start to lose accuracy even just six months after you first open the container’s cap. This is due to the oxidation of the chemicals in the pads of the test strip.

So, always be sure you’re using testing equipment that’s less than a year old or check it against a more accurate testing system, such as the laser readers that you can find at a pool store, every six months.

For more information about testing your pool water, as well as everything else you need to know about owning and maintaining a swimming pool, check out my book Pool Care For Dummies.

Testing strips

The strip will test your sanitizer, pH, and alkalinity at a minimum and some others will also test your cyanuric acid and your calcium hardness. Just follow these steps to use a test strip:

1. Gently dip a test strip into the pool’s water. You can also scoop a sample of water from the pool into a cup and dip the test strip in there. Be sure to reach 18 inches down for the water sample to get the most accurate reading.
2. Hold the test strip horizontally, pads-side up, for 15 seconds.
3. After the 15 seconds, match the colors of the testing pads on the strip to the chart on the back of the bottle.

Using a test strip is simple and quick, and one of the most common ways to check the levels.

There are some downsides to using the test strips, though:

• As simple as they are, it’s a little tricky to get accurate results from them. Most brands recommend a very controlled dip into the water — so no swishing around, and no shaking the test strip off after it’s out of the water. Too much strip jostling may cause colors to appear faded or even bleed into each other.
• The colors on the pad are sometimes hard for the reader to decipher. For instance, the pH is almost always indicated by a shade of red, but not all people can easily tell the difference between one shade of red and the next.

Drop (or reagent) test kits

©Rocklights / Adobe Stock
A drop (or reagent) testing device

When I do weekly service on customers’ pools, I personally use a drop test kit as my regular testing system. There are a lot of different brands that you can try, and a lot of different options. They range from testing only chlorine or pH levels, to being able to test all of the balancing levels in your pool like total alkalinity, calcium hardness, and cyanuric acid along with the chlorine and pH in your pool.

Drop test kids will all have the same components to them, beakers and the little bottles of liquid reagents. Different brands will have slightly different instructions, but the concept with the tests are all the same.

You will fill the beaker with your pool water up to the suggested fill line. There may be two different lines for two different amounts of water, so follow your test kit’s instructions thoroughly. You will then add the appropriate amount of drops of the liquid reagent that is meant for testing the chemical you are looking to check.

Each chemical level you are trying to check, like pH or alkalinity, will all have a separate corresponding liquid drop reagent. You will thoroughly mix the drops with your pool water and it will turn a certain color. Check that color against the color chart provided with your kit and it will indicate if the level you are testing is low, ideal, or high.

I personally don’t have a preference on brand; I’ve used a few different brands and find them all to be accurate. The big thing in selecting your drop test kit is that you want to be able to replace the drop reagents as needed. Worst case is you could replace the whole kit, of course. But if only one bottle runs out or expires, it’s much simpler to get just the drop reagent you need.

I like drop test kits that have the ability to test chlorine, pH, alkalinity, and your pool’s acid demand. (I discuss the importance of those levels in later sections of this chapter.)

Drop test kits can be pricy, depending on the brand you choose. Some of the lesser-known brands can have a price ticket of around $20, but other brands can range up to $100, and they will both test for the same levels!

Higher quality brands tend to be more accurate and reliable, which is where you get the price increase from. The bottles can range in size, but most of them are one or two fluid ounces each and will easily last you a whole season with weekly testing.

Most of the reagent drop-style testing kits are made for halogen (chlorine/bromine) based pools. There aren’t many that are meant for biguanide-based pools. So, if you do have a biguanide pool, you’re usually stuck with strips as your only at-home testing method.

Digital test kits

• Strips that have a corresponding app that you download to a tablet or smartphone: You dip the test strip into your pool water, then snap a photo through the app, and it reads the results for you. But, of course, the app’s accuracy is all based on how precisely you dipped the strip and the lighting in which you took the photo. The concept is great and works reasonably well, especially considering they’re in the lower price range of digital options, around $15 to $20.
• Specialty test strips that have a separate digital reader: With this style, you use the strips like you would any other kind of test strip, dipping them into your pool sample. And then you insert the strip into the reader. The readers are designed to work with only the strips made specifically for it, but they’re quick, easy, and accurate. They’re a mid-price range, usually around $75 to $90.
• All-in-one testing meters: There are two styles of these meters:
  • An electronic testing meter where you dip the sensor into the pool, and the results come up on the meter itself.
  • A floating device that has a sensor in your pool that sends information to an app on your phone.

All of these readers are great ways to step up your ability to check your levels accurately at home, but none of them are perfect. It never hurts to get your pool water tested at a local pool store that you trust (see the following section), or even to check the accuracy of your main testing system with another style (which I go over in the preceding sections). Having basic test strips and a digital floating meter can only help in making you a better pool owner.

Testing at a store

The system used in most pool stores has a high-tech meter that reads small plastic disks that are filled with your pool water. Basically, here's how it works:

• The disk is inserted into the meter.
• The meter spins the disk, mixing the sample water into a variety of chambers along the sides.
• The meter uses lasers to read the colors that those chambers turn.

The meters are usually connected to a computer where the results are automatically entered into a program. That program creates the printout that a pool store employee reviews with you.

This type of highly accurate testing you get at a pool store isn’t something that you do weekly or even biweekly. Your pool’s chemistry can change in that short a time period, but not enough that you need to visit the pool store. If you use a testing system like this too often, you will go slightly crazy trying to get your pool “perfect” when you have an acceptable variance within your levels.

Perfect range for alkalinity is 100 ppm, and if you test it at a pool store and it says your level is 89 ppm, it can get really overwhelming to try to get it exact when 89 ppm is still considered in the acceptable variance. These testing systems are also expensive to run for the pool company, so a majority of them may limit you to only six free tests a year and begin charging for each one after that.

Testing at your pool store should be done

• Two to three days after the pool has been opened and started running
• One week after completing the initial balancing on your first test
• Once a month during the season
• Two weeks prior to the winterization of your pool

Guidelines for water testing at a pool store

• Take your sample from at least 18 inches below the surface of the pool to get an accurate sample and use a container that allows you to get at least 12 ounces of sample water. The pool store may never use that full 12 ounces, but if you need to have extended tests run or have the test repeated, you want to make sure you bring enough water to cover it.
• If you're wondering how to bring pool water to be tested, use a container that has had no other liquids in it, if possible. Acidic liquids such as pickle juice, wine, or orange juice will alter your results. It doesn’t matter how many times you rinse the bottle out, the traces of the acidic liquid distort the numbers, especially your pH. The only safe reusable bottle I would really recommend is an old water bottle.
• If you just opened your pool, don’t bring a sample in until the pool has been circulating for at least 24 full hours. It’s amazing how much your chemicals actually sink to the bottom of the pool over the course of winter!
• Don’t bring in a water sample if you’ve shocked the pool with chlorine-based shock within 48 hours. (You can read about this cleaning process in Chapter 10.) Almost all testing systems are based on the color your water turns when mixed with a certain solution. Just like how chlorine bleaches your clothes, it absolutely lightens the color that the water turns when mixed with the testing solution. This advice goes for all color-based testing systems — if your chlorine is over 8 parts per million (ppm), you probably aren’t getting a very accurate reading.
• If the water turns a certain color when the testing solutions are added, then water that has a distinctive color in the container in which you collect it most likely will be inaccurate when you add those test solutions. If the water in your sample bottle is green, all the colors that your test samples are supposed to turn will be mixed with green, not allowing for accurate results.
• If your water sample has been sitting in your hot car all day at work, its chemistry changes while it’s sitting in the container. If you’re going to bring a water sample somewhere, always be sure to bring it as fresh as possible.

Try not to over-test your pool water. I know that may seem crazy, but just like when you’re on a diet, checking your weight daily doesn’t give you an accurate representation of what’s happening. If you check your pool every day — or even twice a day — you get slightly different results every time. Testing the water isn’t a perfect science, and you’ll make your head spin if you try to make your water’s chemical balance perfect every second of every day.