How To Check Pool Chemicals

How to check pool chemicals

This is a guide on checking your swimming pool or spa chemical levels. Written by www.WCPandS.com. There are a variety of ways to check chemicals, including but not limited to liquid test kits, strip testers, and digital testers (using either vials of water or strips)

Note: Two different types of test kits can each give slightly different readings from the same water samples. None of the three types of test kits are 100% accurate. Choose one type of test kit to check your pool or spa and base all of your chemical needs off of that.

The most commonly checked chemicals that any pool or spa owner should know how to check are the sanitizer (usually chlorine or bromine) and PH levels. While checking the water alkalinity level is also important, it only has to be checked once every xxx days/month(s)/week(s).

Sanitizer and PH

The two most checked chemical levels in any swimming pool or spa are the sanitizer and PH levels. These two are the foundations of healthy pool water and should be checked at least once every week.

The tools needed to check these two are included in almost all water test kits.

Most swimming pools use chlorine as its main sanitizer. However, occasionally,  pools and spas will use bromine instead. Most test kits test the chlorine/bromine levels from 0 to 3-5ppm.

Note: The ideal level of sanitizer for a pool or spa is 3.0.

If you have a liquid test kit, most of these will test for chlorine and bromine with one solution using the same steps for both.

How to check the chlorine/bromine with a liquid test kit:

1) Fill the chlorine/bromine side and then the PH side of the test beaker to the levels shown on the beakers.

(Pic of beaker with correct amount of water while pointing out the fill line)

2) Add 5 drops of the #1 solution. (pic of adding drops to chorine side of beaker)

3) Add 5 drops of the #2 solution to the PH section of the beaker. (pic of adding to PH side)

3) Mix. (pic of mixing solution and water)

4) Match the color of the mixed water with the side color guide to determine the level of the sanitizer/pH.

This really comes down to looking for specific colors.

For chlorine you want bright yellow. Light yellow or clear needs chlorine. Orange or red is too much chlorine.

For pH a pink or a light red color is ideal. Purple needs acid. Orange or Yellow needs soda ash.

Below are a few examples.

Note: Do keep in mind that these shades will look different when you do them because of the different color properties from the camera taking the pictures, the photo editing software used to edit the pictures and your home computer screen setup. 

An ideal chemical reading CL2.0 pH 7.6

Cl 0.2 pH 7.2 Needs chlorine and soda ash

Cl 2.0 pH 7.8 Needs acid

Cl 1.0 pH 7.0 Needs chlorine and soda ash

Cl 1.5 pH 7.6 Needs chlorine

Cl 2.0 pH 7.3 Needs soda ash 

If you have a test strip kit, check the instructions to see if your kit will test for chlorine or bromine. Though it is not uncommon for test strip kits to offer testing for both, most will only test one or the other. The option for also checking the pH level is common for most test strips.

The instructions for strip tests can vary slightly from one manufacturer to another. In general, they involve placing a test strip underwater for a few seconds, then removing it from the water and comparing to the color guide usually found on the side of the test strip container.

How much sanitizer to add

There is no set answer to how much sanitizer should be added to change the levels by a specific amount. This is because after adding chlorine/bromine to a pool, there could be things in the water that will “use” the sanitizer, causing the levels to drop back to zero in just a few hours. What you will want to do is add a little and see how that changes the chemical levels. If the pool or spa needs more, you can always add more. What you don’t want to do is add too much and have to remove chemicals that you just added.

For chlorine used in a full sized pool, add 1/2 gallon of chlorine, wait about 20 minutes, and then recheck the chlorine level. 

If the pool is smaller than the average sized (less than 10k gallons) pool, you will want to add less, from .25 gallon or less at a time.

How much is too much chorine/bromine

This can be difficult to determine since most test kits readings will max out between 3-5ppm. One of the ways to tell if the chlorine level is too high is by the color of the beaker after adding the testing solution. 

At 3.0, the chlorine/bromine test side will be a bright yellow. As the level goes up, the colors will change from yellow to orange to an orange red. See the example readings above.

If the color of your beaker is orange or darker, do not add any more chlorine/bromine. You should also remove any tablets from a floater, or automatic feeders, and/or turn off salt systems (if your pool has one).

If your beaker color is orange or darker(higher), your skin feels drier than normal after using the pool or spa, and/or you develop a rash after using the pool or spa, sanitizer should be removed from the water. A sanitizer remover can be purchased from most swimming pool supply stores.

How much acid or soda ash to add

Note: The ideal PH level is 7.4 – 7.6

The PH level is ideally 7.4-7.6 and needs to be moved slower than the chlorine levels. If you add too much chlorine, it will not damage the equipment or cause injuries but it might dry the skin of anyone that swims in the water. However, changing the PH level too far any one way could damage the pool or spa plaster and/or equipment.

Note: Adding too much acid can cause heater damage, copper sulfate stains in the plaster, and/or equipment damage.

Note: Adding too much soda ash can cause water scaling, tile calcium buildup, and lead to ineffective sanitizers.

To lower the PH, use either liquid or dry acid.

Liquid acid is the most common and cheapest way of lowering PH. If you are adding acid to an average sized pool, only add 1/4 gallon of acid at a time. While the system is running, wait 30 minutes or longer, then retest. If the PH level is still 7.7 or above, repeat this step until it reaches the desired level.

For dry acid, check the instructions since the usage amounts will vary.

To raise the PH level, use a soda ash product. Check the instructions that come with the soda ash to determine the amount needed.

Note: Do not use baking soda. Since baking soda was not intended for use in pools or spas, its application is complete guess work. Experimenting while trying to find the correct usage amounts can cause damage to your pool or spa.

Testing the Alkalinity level

Alkalinity can be tested on some liquid and strip test kits. This should be checked when the PH level changes too much or not at all after adding acid or soda ash.

Note: The ideal alkalinity level is between 80-120ppm

Steps for checking alkalinity with a liquid test kit

1) Fill the PH side of the beaker with pool/spa water to the line marked for the alkalinity test on the pH side of the beaker.

2) Add one drop of solution #4 to this water sample, then mix.

3) Add one drop of solution #5 to this water sample, then mix. The solution will turn the water to a light purple tint.

4) Add one drop of solution #4 to this water sample, then mix.

5) If the water sample is still purple, add another drop, then mix. Keep count of every drop of solution #4. Continue adding a drop, mixing, and checking for a color change until the color changes to clear.

 When the water turns clear, multiply the number of drops of solution #4 used to make the water clear by 10 and that is the alkalinity level.

So if it took 8 drops for the water to turn clear, 8*10 is 80, the alkalinity level in this example is 80. Remember that the ideal alkalinity level is between 80-120ppm.

Now the process done in a video:

The purpose of the test above was only to determine if the alkalinity was too low, just right or too high.

- To find if it is too low add 7 drops then mix. If the solution goes clear the alkalinity is low.

- If the solution was still purple add an additional 5 drops (for a total of 12 drops) then mix again. If the solution is clear the alkalinity is within its proper range.

- If the solution is still purple the alkalinity is high.

To learn more about alkalinity and pH, see our alkalinity write up here.