Water Test Fails: 12 Simple Mistakes You Could Be Making

Dr. Pool water testingWelcome back, students of pool! I’ve spoken on the topic of pool water testing before, and we also have a nice beginner’s guide to pool water testing.

Today’s pool testing guide covers some of the finer details of conducting backyard water analysis, and a few common pitfalls of using an outdoor laboratory.

Pool water testing can become so routine that you may not realize these simple mistakes could make your test results inaccurate. There are 12 pitfalls to avoid when testing your pool or spa water:

1. Water Sample from the Wrong Area of the Pool

Where you gather your water sample from in a swimming pool matters. Avoid areas near return lines, steps, ladders and corners of the pool. These are locations in a pool where the pool chemistry is going to be different from the pool as a whole.

proper-water-sample-techniqueIn order to get an accurate sample of your pool water, don’t draw the water from the surface because that is where the highest concentration of pollutants like oils and debris gather. The surface is also where evaporation is taking place and the interaction with the air can throw your results off. As a rule of thumb, an elbow deep depth between the shallow and deep ends of the pool is the sweet spot.

2. Not Testing the Sample Immediately

You pulled the sample from the perfect area and depth of the pool but didn’t test it right away. Life is full distractions – letting a sample sit too long gives it time to react with the air, sunlight, and even humidity. Commit to the process!

3. Tilting The Reagent Dropper

testing-pool-waterThis is one of the small details that can make a big impact on the accuracy of your test results. Tilting a reagent bottle as shown, instead of holding it straight up and down will make the drop smaller and throw everything off. If your test kit includes tablets, remember to crush them fine. Just like drops, cutting corners on this step will ruin the chemical reaction. Speaking of proper measurements…

4. Too Little or Too Much Water Sample

Even the slightest inaccuracy of a water sample can skew your test results. It may only be a few dozen drops of water, but too little or too much can tip the scales. Precision is key when it comes to achieving the best results possible. Hold your test vial at eye level and the bottom of the meniscus or curve of the water should be lined-up with the “Fill” level line.

5. Not Swirling the Sample

You followed steps 1-4 perfectly, and added the perfect amount of reagent into the perfect amount of water and in all the excitement, didn’t swirl between drops. Take your time and mix the reagents thoroughly. Holding the comparator on the top between your thumb and forefinger, and rotate your wrist to swirl the sample within the test vial.

For the titration tests (FAS-DPD, pH demand, Alkalinity & Calcium), if you are unsure if the sample color has changed completely, add another drop. If you do not see a change, just subtract that drop from your count. Or when the color changes color briefly, and one more drop changes it completely, you can count the last drop as 5 ppm, instead of the normal 10 ppm.

6. Expired Test Reagents

pool water test reagentsPoring over every detail during the testing process could all be in vain if your pool water test chemicals were compromised before you even pulled your first water sample. It’s best to begin each season with fresh reagents. Typically, the chemicals used in test kits are considered to have a shelf life of about a year.

7. Improperly Stored Reagents

The best test kit money can buy can be rendered useless due to improper storage. The shelf life of pool test chemicals can be greatly impacted by hot and cold temps. Ideal storage temperatures are between 5° to 22°C (40° to 70°F). Bear in mind, that a constant fluctuation of temperature can also negatively impact the chemicals. Store pool test kits in a cool, dark place, and avoid prolonged exposure to the sun.

Frozen Test Reagents: Water test kit makers suspend shipments of liquid test kit chemicals during freezing weather, however water test chemicals may still be viable after freezing for a short time period. Allow frozen reagents to thaw at room temperature. If the bottle has cracked or if there are crystals around the tip, or particles floating in the bottle after shaking, you should replace the reagent.

Clear Reagents Turning Colors: Taylor reagents 1, 2, 3, 5, 6, 7, 9, 10 and 12 should be colorless and clear. Drop a few drops onto a flat part of the testing vial; if the drops look cloudy, or are any color other than clear transparent, you should replace the reagent.

Colored Reagents Changing Colors: Taylor reagents 4, 8 and 11 are colored indicator solutions. Reagent 4 or pH Indicator is red, while reagent 8 or Total Alkalinity Indicator is green and Calcium reagent 11 is a blue color. If another color, you should replace the reagent.

Colored Reagents Staining Bottle: Taylor reagents 4, 8 and 11 should not stain the bottle in which they are contained, which indicates a separation of the test pigment. If the reagent bottle is stained, you should replace the reagent.

8. Cracked or Faded Comparator Vials

Taylor test kit comparators and other test kit partsSimilar to reagents, a cracked test vial or comparator can lead to pollutants spoiling your results. Even a faded or slightly scratched test vial can open the door to particulates that have no business getting mixed up with your perfectly swirled reagents. If the test vial or optical chamber looks old, faded or perhaps slightly stained—it’s time for a new test vial.

9. Using Test Reagents From a Different Test Kit

You can’t mix and match test kit reagent chemicals; this isn’t a matter of brand loyalty. Pool test kits vary by manufacturer and even the slightest variation of pool test chemicals strength and dropper orifice size can (everyone in unison) Render-Your-Test-Results-Inaccurate. Where have we heard that before? While we are on the topic of mixing and matching…

10. Mixing Test Reagent Bottle Caps

When you are done with a pool test chemical it is important to put the cap back on immediately. Not only does this help protect it from reacting with environmental variables it can prevent putting the wrong cap on the wrong bottle. Even if both caps are the same color (more reason not to delay), the chemicals under the caps are certainly not and a little bit of residue is enough to unravel the fabric of the universe – or at the very least, cross contaminate your reagents and you know that is a gateway to trouble.

11. A Clean Test Kit is an Accurate Test Kit

Don’t touch the tip of the dropper bottles with your fingers. Exposure to these chemicals could irritate your skin and also the oils from your fingers can contaminate the drops. In addition to a clean reagent dropper bottle, thoroughly rinse out the test vials or optical chambers after testing. Lingering chemicals from a previous test is a surefire way to ruin your next test.

12. Misreading The Color Chart

As cool as you look in your sunglasses, take them off when reading discerning the hues on the optical chamber. Perhaps this is obvious, the tint of your sunglasses can make 7.5 look like 7.6 on the color scale.

esting-water-with-sunglassesHand-in-hand with removing your sunglasses is making sure you are not holding the optical chamber up to an artificial light source, or anything other than a white background (the purpose of the white rectangle, found in some test kits). A blue sky or blue water background can lead to a green pool when you misread test results.


If there is one key aspect of pool maintenance where spending more will ultimately save you money in the long run, it’s using a high quality test kit from a reputable manufacturer. Cut corners in this area and you could end up spending more on chemicals attempting to restore water balance and fight water problems.

I highly recommend the Taylor K-2005 test kit (and K-2006), and the ColorQ Pro7 by LaMotte, and greatly prefer the accuracy of liquid test kits over the convenience of test strips because, in pool chemistry, accuracy is king!

talk-to-us!Did we miss a tip or have a pool question you need answered? We love to hear from the In the Swim Pool Community! Please feel free to email us @ socialmedia or reach me directly @ Dr. Pool.


Dr. Pool



Water Test Fails: 12 Simple Mistakes You Could Be Making — 3 Comments

  1. Pingback: Slash Swimming Pool Maintenance Costs | InTheSwim Pool Blog

  2. New at this. Pool is a 25 x 4. I figure 32,000 to 33,000 gal?
    Chlorine is 0
    I’ve added 9 gallons bleach over 3 weeks and have shocked weekly.
    Ph is 7.8 maybe a little higher
    Alkalinity is 80
    Total hardness is 200
    CYA is 0. Added 2 pounds of stabilizer yesterday and 3 clorine tabs. Same readings today. Going to add another 2 pounds of stabilizer today.
    Pool is above gound

    • Hi, drop the pH down to 7.2, and the chlorine will be twice as active (and powerful). You should begin to see the effect of the stabilizer right away. With a lower pH and stabilizer level, you should begin to test a chlorine level, If not – shock one more time with 5-6 lbs of cal hypo.

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