Hot Tub Water Testing: How To Test Your Spa Water Chemistry



Before you can relax in your spa, you need to ensure that it’s clean and safe for use.

Contaminated hot tubs are full of bacteria, viruses, and pathogens that can cause sickness and disease in bathers.

Through hot tub water testing, you’ll be able to monitor the condition of the water, so the spa can be used at any time.

When (And How Often) To Test

Hot tubs are great but they do require a committed maintenance schedule when it comes to testing and balancing the water chemistry.

When pollutants and hot water mix, bad things take root. A hot tub has a high likelihood of forming bacteria and algae unless the proper amount of sanitizer is used.

Regular testing allows you to keep the water at a neutral pH level, as well as proper levels of total alkalinity (TA) and chlorine (or any other sanitizer).

At a minimum, you should be testing the water anywhere between 2 and 3 times per week. If the tub is used frequently, or by a high number of people, you should increase testing frequency.

Reasons to test regularly?

  • It keeps the water’s essential levels balanced: pH, total alkalinity, and calcium hardness
  • You’ll know when the water needs more sanitizer so people don’t get sick 
  • To prolong the lifespan of the hot tub, as unbalanced water causes water issues which can affect the structure
  • You’ll use less chemicals by frequently testing and adjusting in small increments rather than fixing a large water problem
  • You’ll save money on the amount of chemicals you have to use

How to Test Your Hot Tub Water (3 Methods) 

Testing the hot tub’s water is very easy to do.

Each of these methods require you to take a sample of the water, which can you do by following these steps:

  1. Position yourself away from the skimmer and any return jets
  2. Using a cup, plunge it upside-down, elbow deep into the water. At this depth, it ensures the chemicals in the sample have been well-circulated.
  3. Flip the cup over so it fills up with water.
  4. Scoop out the water.

Now that you have your sample, let’s explore what you can use to test it.

1. Testing Strips

The most convenient way to test your water is with test strips. 

These are color-coded paper strips you match to a chart on the bottle which shows you if your levels are too high, too low, or just right. While you’ll go through a lot by testing multiple times a week, they’re inexpensive and the preferred testing method of most hot tub owners.

The most basic test strips will test for pH, TA, and and chlorine, although you can easily find 5 in 1, or 6 in 1 strips that will include things like calcium hardness and other chemical levels.

How to use testing strips on your hot tub:

  1. Take a sample of water from the hot tub.
  2. Dip the strip into the sample.
  3. Wait 15 to 30 seconds for the colors on the strip to change.
  4. Consult the chart on the back of the bottle by matching up your strip.
  5. If the levels aren’t ideal, adjust the hot tub water as needed.

2. Liquid Testing Kits

Liquid testing kits can, at times, be slightly less accurate than test strips, and are also more involved when it comes to using them. 

They require you to add reagents to 2 water samples and record the results. This is where accuracy issues come into play, as an extra drop of the reagent can skew the result.

The main reagents you’ll add to the water are OTO (orthotolidine), and phenol red. OTO measures the water’s chlorine level, while phenol red measures pH level. Additional reagents will test for other chemical levels.

Provided you add the proper amount, liquid kits can be very accurate. But their more involved process compared to the ease of simply dipping a test strip in a cup of water turns many people off of this method.

How to use liquid testing on your hot tub:

  1. Using the sample holder the kit provides, dip it into the pool water and take your samples.
  2. Add 4 to 5 drops of the reagents to each water sample.
  3. Shake up the samples and wait a few seconds until the water changes color.
  4. Compare the water sample to the corresponding colors on the tester. Keeping a piece of white paper with the tester will make it easier to decipher color shades.
  5. Adjust the chemical levels in the tub if needed.

3. Digital Test Kits

If accuracy is what you’re aiming for, get yourself a digital test kit. 

Digital testers are easy to use and test for a wide range of chemicals in the water, including some you might not even be using in your tub. For people with poor eyesight, a digital tester makes things a lot easier so you’re not struggling trying to match color shades.

Of note, they are about as involved as liquid kits, with many digital testers requiring a reagent to be added to the water sample.

The big downside of going digital is that the really good ones are quite a bit more expensive than strips or liquid kits, hovering in the $200 range. 

How to use digital test kits on your hot tub:

  1. Take a sample of the pool water using the provided sampler included with the kit.
  2. Add any reagents if they’re required.
  3. Depending on the tester, you may dip it into the water sample (like a digital thermometer), or you may add the water sample to a testing block.
  4. Record the results.
  5. Adjust the chemical levels in the hot tub if needed.

Consider Going For A Store Test

Testing is something you need to learn to do on your own, but at some point, you may want to bring a sample of the hot tub water to a store and have it tested by a professional.

They will give you accurate readings of everything in the water, and you can consult them regarding balancing the water if there are any issues with it.

A lot of times, pool and spa stores will provide this service for no charge. 

What Should You Be Testing For?

Let’s take an in-depth look at what levels you should be testing for and why.

How To Test pH

pH is the measure of how acidic or basic (alkaline) the water is. The best pH level for your hot tub water is between 7.4 and 7.6.

If it goes above this range, you’ll run into problems with ineffective chlorine, mineral deposits at the waterline and inside pool equipment, and potentially even health issues like itchy eyes, skin, and irritated nasal passages.

You can bring it back down using pH Decreaser (which is predominantly sodium bisulfate), or muriatic acid.

If it falls below this range, you’ll experience the same itchy irritation issues, as well as corrosion of the tub’s equipment. Raising the pH level can be done with either soda ash or baking soda.

You can test for pH using any testing kit, as it’s one of the most important (if not the most important value to test for).

How To Test Total Alkalinity

The job of total alkalinity is to stabilize the pH level in the water. Without it, you’d have a hot tub where the pH fluctuates dramatically, causing all sorts of problems. 

The ideal level of TA is between 80 and 120 ppm.

Above 120, the chlorine will become inactive, and your tub will be dealing with an infestation of bacteria, viruses, and pathogens. TA can be brought down by using a pH Decreaser in the water. 

If your water is testing below 80 ppm, it’ll cause the pH to drop, which then leads to corrosion of equipment, and irritant issues for bathers. You can bring it back up using baking soda or an Alkalinity Increaser product.

Like pH, TA is one of the main levels that test kits across the board will test for. 

How To Test Calcium Hardness

The amount of calcium in the water refers to how hard it is. In hot tubs, calcium hardness is required to stabilize both the pH and TA levels.

You’ll want to keep the calcium hardness between 175 ppm and 250 ppm at all times.

When there is a spike in calcium, issues like cloudy water and scale will present themselves. It also causes the other chemicals in the tub to be ineffectively dissolved. To lower calcium, your best plan of action is to drain the tub and wash it before refilling and starting over.

When soft water is an issue (meaning there’s a low level of calcium), it will slowly eat away at the hot tub shell, as well as the plumbing and equipment.

Calcium hardness is a pretty common value that most every kit will test for. Double check to be sure, so that you won’t have to purchase a separate calcium hardness test strip or kit.

How To Test Sanitizer

Sanitizers for your hot tub are a must to keep dangerous pollutants out of the water, protecting bathers in the process.

The most common sanitizer for hot tubs is chlorine. Bromine is a popular choice for covered or indoor tubs, and biguanide is another option you can use (though it’s less common).

Chlorine requires a level of 1 to 3 ppm, bromine 3 to 5 ppm, and biguanide uses 30 to 50 ppm.

When sanitizer levels get too high (especially with chlorine), itchy skin, eye and nasal irritation will occur. Lowering levels like chlorine and bromine can be done naturally by not using the tub until the levels dissipate. If you’re in a rush, you can use a Decreaser product.

On the flipside, a tub without enough sanitizer can’t destroy pollutants and is at greater risk of an algae bloom. Raise those levels quickly by adding more of your sanitizer of choice.

Sanitizer is extremely important to the health of your hot tub, so most kits will test for at least chlorine.

However, some will only test for total chlorine, and you may need additional values for free chlorine (to calculate your combined chlorine). Additionally, bromine and biguanide usually require separate test strips, as they’re less common sanitizers.

How To Test Salt

Many people like that salt water hot tubs are less harsh on their skin, hair, and swimwear. Salt systems actually convert the salt in the tub to chlorine, with ideal levels being 2,000 to 3,000 ppm (salt), and 1 and 3 ppm (chlorine).

As these are essentially still “chlorine” tubs, all the same issues apply if the salt and chlorine levels spike or drop.

In most cases, testing for salt will have to be done using a dedicated testing strip. Some high end digital testers may include it, but if not, you can always pick up a digital salinity tester for accurate measurements.

How To Test Cyanuric Acid

Hot tubs that are exposed to sunlight will need to add cyanuric acid (CYA) to their water to protect the chlorine from rapidly disintegrating. 

CYA levels should be between 30 and 50 pmm for adequate protection. 

If there is too much CYA in the water, this will lead to chlorine lock, a phenomenon where the chlorine literally locks up and stops working.

If CYA is under 30 ppm, there won’t be enough of it to protect the chlorine from the sun, and the sanitizer will be destroyed quickly. No chlorine in the tub = no bueno.

Testing for CYA can usually be done using strips that test for multiple values, and most liquid and digital test kits will also account for it.

How To Test Metals

Hot tub water will always have some level of metals in it, and some owners even go the route of using mineral sticks with sanitizer for a more gentle tub.

Mineral sticks are easy to use and last 3 to 4 months, slowly releasing the correct dosage over time. By using minerals, the tub will use less chlorine (0.5 ppm), or bromine (1 ppm).

Minerals aside, high levels of metals cause problems with your tub water. Excessive amounts of copper, iron, and manganese can turn your water green or brown as it reacts to the metals in it. If not taken care of, it can lead to staining of the tub shell.

Testing for metals is usually done using specific test strips, which will provide you results for a wide range of potential metals in the water.

Hot Tub Water Testing: Simplified!

Hot tub water testing is an important part of being a responsible tub owner.

Regularly testing with strips or test kits will allow you to make the proper adjustments your hot tub needs to stay clean and safe for bathers.

Categories: Hot Tub Care, Hot Tub Chemistry