Hot Tub Chemistry: The Chemicals You Need For Proper Balance



Hot tubs are one of the most relaxing luxuries you can have in your home.

But before you can jump in, you’ll have to make it safe to use.

Large bodies of water that sit dormant for long periods of time can become health hazards that people should not go in.

Maintaining the hot tub water chemistry is what will allow you to spend endless hours in total relaxation. 

It All Starts With Testing

Unless your hot tub water has turned a funky color, the only way you’ll be able to know if it’s clean is by testing the water.

Testing should be done on a regular basis, at least once a week, and even more frequently if the tub is seeing more than normal use.

Water can be tested a number of different ways.

The easiest way is with test strips. These are inexpensive, color-coded paper strips that can test for multiple chemicals in the water at the same time. You simply dip the strip into a sample of the hot tub water, and wait a few seconds for the results.

Liquid testers are another option. Using a water sample, additives are added to it that create a reaction to show you the chemical level. Liquid test kits are more accurate than test strips, but are also a more involved process.

The top of the line testers are digital test kits, in which you dip the tester into the water sample to get the chemical readings. While these are the most accurate, they’re also the most expensive option.

Balancing The Basics

No matter what chemicals you put into your hot tub, there are 3 must-haves that are always required, and form the basis of your water’s chemistry.

pH Level

pH is the measure of how acidic or basic (alkaline) the water is. Balanced pH creates the right environment for the rest of your hot tub chemistry.

The ideal pH level for your hot tub water is somewhere between 7.4 and 7.6.

If it goes above this range, the water becomes alkaline and you’ll run into problems with scale in the water, which can potentially clog your plumbing. You’ll also experience itchy skin, irritated eyes and nasal passages.

Fortunately, high pH can be fixed by adding muriatic acid or sodium bisulfate to the water to bring it back to a neutral level.

If it falls below 7.4, the water becomes acidic, and you’ll start to see the same eye/nasal/skin irritation issues, and the water will start to corrode surfaces and equipment.

Low pH can be fixed by adding soda ash (sodium carbonate) or baking soda (sodium bicarbonate).

Total Alkalinity

Total alkalinity (TA) is the total concentration of dissolved carbonates, bicarbonates, hydroxides and cyanurates in the water. It’s job is to act as a pH buffer, which keeps the water’s pH level from wildly fluctuating.

Ideally, you want to keep the TA level anywhere from 80 to 120 ppm (parts per million).

If TA drops or rises, you’ll see a fluctuation in the pH level of the water, causing an acidic or alkaline hot tub. 

A high alkalinity tub will render the chlorine in it useless, leading to things bacteria-infested green water, and scale build up.

If the water has low TA, corroding of the hot tub, equipment, as well as delamination of the tub’s shell will occur.

To bring the alkalinity level up, you can use baking soda or Alkalinity Increaser. 

Unfortunately, to lower the TA level, there is no Alkalinity Decreaser. Instead, you’ll need to use a pH Decreaser, which lowers both the pH and TA. Once the TA is back in an acceptable range, you can raise the pH if needed.

Calcium Hardness

Calcium hardness refers to the amount of calcium that is present in the water. While many people spend money to avoid hard water in the home, hot tubs need it.

Keeping your hot tub calcium hardness between 175 ppm and 250 ppm will help it stabilize the pH and TA levels.

If the water is too soft (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.

If the calcium gets too high, it can lead to cloudy water, scale issues, and ineffective dissolution of the other chemicals in the tub.  If this happens, the best way to restore the calcium level is to drain the tub, scrub it down, and refill.

Adding Sanitizer

Hot tubs require sanitizer to not only keep the water clean, but to keep the people using it from getting sick. There are several choices you can pick from:


By far the most common hot tub sanitizer, chlorine comes in powder, liquid, or tablet form, and kills a wide range of water pollutants. It’s also cost-effective and simple to add to the tub, making it a popular choice.

The ideal level for chlorine is between 1 and 3 ppm. Failure to keep it in this range will lead to water problems. Not enough chlorine can lead to bacteria, viruses, and fungi taking hold of your hot tub. 

Chlorine oxidizes organic pollutants, and the oxidation results in a gas known as chloramines, which is that pungent chlorine smell that hot tubs can get. Chloramines are an irritant to your eyes, skin, and nasal passages.

If your tub smells very chlorine-y, there’s a good chance it’s very dirty and there’s not enough chlorine in the water. 

Conversely, when the water has too much chlorine, that will also lead to irritated skin, eyes, and nasal passages.

Adding chlorine to the tub is simple to do. Sodium dichlor is a popular choice for hot tubs that aren’t in direct sunlight, as it won’t overly affect the pH level and it doesn’t contain any stabilizer (cyanuric acid aka CYA). CYA prolongs chlorine’s lifespan by protecting it from the sun’s UV rays. 

If your hot tub is exposed to direct sunlight, you’ll need to go with a chlorine that has CYA built-in (stabilized chlorine), or you’ll have to add CYA to the water separately.


Bromine can be used as a hot tub sanitizer as well. While chlorine oxidizes (creating chloramines), bromine ionizes. This destroys pollutants by breaking them apart at a molecular level. 

While it’s an effective water cleaner when kept between 3 and 5 ppm, the breakdown of bromine creates bromamines. These aren’t as pungent as chloramines, but they lessen the effectiveness of the bromine.

The easiest way to add bromine is with tablets in a floating bromine feeder. All you have to do is add them to the feeder, place it in the hot tub, and watch it float around distributing the chemical.

The main advantages of using bromine over chlorine? It’s less harsh on your skin, lasts longer, and its low pH helps keep the water balanced. However, it does work slower, which means pollutants stay in the water longer before the bromine takes care of them. 

Unlike chlorine’s stabilizing agent of CYA, bromine doesn’t have one. So you can only use bromine if the tub is out of direct sunlight, or indoors.


A chlorine-free and bromine-free alternative is biguanide, which goes by the brand name Baqua Spa.

It’s sold as a stand-alone sanitizer, but most spa owners splurge on a 3 pack of Baqua Spa chemicals. This includes a waterline controller to prevent deposits from damaging the spa shell, and an oxidizer to rid the water of organic compounds.

Ideally, you should keep your biguanide levels between 30 and 50 ppm for round the clock sanitation. Biguanide can be easily added to the tub by simply pouring it in.

Biguanide gives the water a silky smooth feeling, doesn’t smell, and lasts longer than both chlorine and bromine. The downside is that it’s the more expensive option, and has been reported to cause deterioration of spa gaskets and plastics in some cases.


Saltwater spas work much the same as saltwater pools, providing a more gentle feeling on your skin due to the use of salt.

What many people don’t know is that salt systems require a salt chlorine generator, which converts salt into chlorine.

With these systems, ideal levels of salt is between 2,000 to 3,000 ppm, and chlorine between 1 and 3 ppm

Salt is added directly to the water and it’s circulated through the system. The salt generator then converts it to chlorine which is then sent back to the tub through the return jets.

Aside from being a gentler chemical, the upside of using salt is that it’s cheaper than chlorine. However, the salt generator itself can get into the 4 figure range.


Cleaning the spa with minerals is another route you can take. Copper and silver help to eradicate algae and bacteria, respectively.

However, they can’t sanitize everything that may be in the water. For this reason, you’ll still need you to use chlorine or bromine, but at a lower dosage.

Chlorine will only be 0.5 ppm, and bromine at 1 ppm.

Minerals are available as a dosing stick which gets added to your pool filter, and dispersed over time into the hot tub.

With softer water and zero chloramines being produced, it’s certainly an attractive option. While the sticks are inexpensive and you don’t have to measure the dosage, you do have to replace them after 3 or 4 months.

Shock Treatment

Shocking is the process of adding a mass amount of chlorine to the water when it becomes out control (ie. cloudy/full of algae). 

As a proactive measure, you should be shocking your hot tub at least once a week to keep the water it’s cleanest, especially if you have a heavy bather load.

Shocking requires you to raise the free chlorine level of the water by at least 10 times the amount of the combined chlorine level.

Depending on your sanitizer, you may need to use chlorinated or non-chlorinated shock.

Chlorine, bromine, and saltwater tubs can use both chlorinated or non-chlorinated shock, whereas mineral systems use non-chlorinated shock to keep chlorine levels low. Biguanide brands will have their own specific shock that must be used with their sanitizing chemicals.

Using Specialized Chemicals

Aside from balancing the basics, let’s take a look at a few other chemicals your hot tub may require.


Algaecide is a biocide used to kill and prevent algae from growing in your water. When algae starts growing in your tub, it will be hard to miss as the water turns a nice shade of green, yellow, or pink.

Algaecide products vary, so you’ll have to consult the bottle’s instructions to calculate the proper dosage for your tub. Adding it can be done simply by pouring it in.

A staple when it comes to hot tub maintenance, algaecide is usually added weekly as high water temperature mixed with high pollutants are ideal conditions for an algae bloom. 

Cyanuric Acid

We briefly touched upon CYA earlier, so you know it’s a stabilizer for chlorine. You can think of it as sunblock, protecting chlorine from breaking down when it’s exposed to the sun’s UV rays. It also helps chlorine last up to 8 times longer.

CYA is a must-have if you are using chlorine as your sanitizer and your hot tub is positioned in the sun. If it’s shaded or indoors, no CYA is needed.

Stabilized chlorine has built-in CYA, and unstabilized chlorine means you’ll have to add CYA separately.

Ideally, CYA levels should be between 30 and 50 ppm

Adding it to your hot tub should be done by diluting the acid in a bucket of water and pouring it into the tub. As it’s an acid, be sure to wear the proper protective gear (chemically-resistant gloves and goggles).

High CYA levels can become troublesome as it will slow down the effectiveness of chlorine, leading to an increase in bacteria, viruses, and pathogens. It can also damage surfaces and equipment, and cause inaccurate pH and alkalinity readings. 

Adding CYA separately is usually preferred, so the level is kept under control, as the only way to rid the water of it is by draining your tub.


Clarifier’s main function is to clear up cloudy water, but it’s also designed to keep your pH level intact and increase the performance of your filter.

It works by clumping up small particles in the water so they can easily be removed with a skimmer net, or through the filter.

To use, all you have to do is consult the instructions on the bottle for the proper dosage, pour it into the pool and wait a few minutes.

Clarifier is a quick fix for cloudy water but you’ll have to address the root cause of your water problem eventually.

Cleaning Agent

Cleaning your hot tub doesn’t doesn’t always require a specialized chemical. Many times you can use everyday household cleaners.

Detergents, bases, acids, sanitizers, and abrasives can all be used to tackle your tub. 

Aside from being inexpensive, white vinegar has a pH of 2.5 to 4.0, making it strong enough to dissolve debris along the waterline, while not eating through the tub shell at the same time.

Sticking with salad ingredients, olive oil is another option. Pairing it with mild soap can help it remove other oils that hot tub stains may be covered with.

Bleach is another good one. It works on stains by not only breaking up their bonds, but sanitizing as well. This is a great option to get rid of waterline scum that vinegar has a tough time handling.

It’s important to note that bleach should only be used as a standalone cleaning chemical, and you should fully rinse the tub before and after use.

If you’re looking for a mild abrasive, water mixed with baking soda can do the trick. With a little elbow grease and a sponge, you can easily clean a variety of dirt from most surfaces.

Other household cleaners you can use are rubbing alcohol, Simple Green, or a Magic Eraser brush.

Diluted rubbing alcohol works well to clean stainless steel/chrome fixtures, while Simple Green is an all-purpose cleaner that’s both biodegradable and non-toxic, allowing you to clean all facets of your tub. 

The Magic Eraser brush (melamine sponge) is a mildly abrasive foam that can remove almost any dirt or stain from surfaces and cracks.


Enzymes are protein molecules that produce chemical reactions.

In hot tubs, their role is to begin decomposition of non-living organic matter, breaking them down into smaller molecules. This makes it easier for chlorine or bromine to destroy them.

Enzymes are an attractive option when it comes to your chemical usage. As they lend a hand, the sanitizer won’t be used up as much, or as quickly.

This also translates to money saved on chemical top-ups, and the time between shock treatments will be prolonged.

Maintaining Your Levels

There are a few actions you can take to help give your water the best chance of staying clean. 

Test Regularly

Testing the water on a regular basis is a non-negotiable. 

By keeping on top of all the proper levels in the water, you’ll stand a better chance of being able to restore the chemistry if anything starts to peak or drop.

Once you get into the habit of regular testing, you may even be able to predict when the water chemistry will change, leading to faster solutions, and less potential headaches.

Check Your Filter

The filter plays a big role in the cleanliness of your hot tub.

While the sanitizing chemical in the water will destroy contaminants, without a hot tub filter in your system, those contaminants will stay in the water. The filter removes them so you’re not bathing in filth.

Over time the filter gets dirty and will need to either be cleaned or replaced. Cleaning it every 2 weeks will help prolong the filter’s life. 

With hot tubs you can use sand filters, cartridge filters, ceramic filters, or DE (diatomaceous earth) filters. The most popular type for hot tubs are cartridge filters, which allow you to easily rinse or replace them.

Shower Before Use

You see this policy implemented at most public pools, but showering before getting into your hot tub is a good idea. 

By showering, you’ll be washing off all kinds of pollutants from your body so they  don’t end up in the tub. These are things like body oils, sunscreen, shampoo chemicals, hair, and even skin.

With less contaminating materials in the tub, the sanitizer will last longer, and you’ll save more money.

Cover Your Tub

Putting a lid on your tub has many benefits. 

First and foremost is safety, as you don’t want anyone or any animals to accidentally fall in and drown. Second, it will allow you to keep out any backyard debris which could dirty up the tub.

A cover will also protect the tub against evaporation, which is more prominent when the water temperature is warm. Additionally, if inclement weather hits, the cover can protect the water and the interior shell as well.

Give It A Good Scrub

With practice, you’ll develop a hot tub maintenance routine that should be done once a week, with a full drain and water replacement every 3 to 4 months.

Using a hot tub cleaning product, or the household products listed earlier in this article, you should have no problems making it shine.

You Don’t Have To Be A Chemist

The truth about caring for your hot tub is that it isn’t all that difficult. 

By paying attention to the hot tub water chemistry through testing, you can top up the proper amounts of chemicals when needed.

Finish caring for it by scrubbing it down and you’ll have a tub that is ready to use at all times.

Categories: Hot Tub Care, Hot Tub Chemistry