Affordable Hot Tub Repair

Find us on YelpText or Call: 619-342-5442Find us on Facebook

Contractor's License: 977562

Simple Hot Tub Chemistry - Sanitize & Shock/Oxidize


Hot Tub Repair

Hot Tub Covers

Simple Hot Tub Chemistry

  1. Hot Tub Chemistry Fundamentals

  2. Why you can't treat a portable hot tub like a Swimming Pool

  3. Total Alkalinity & pH

  4. Sanitize & Oxidize

  5. Step-by-Step Hot Tub Chemistry Checklist with dosage tables

  6. Simple Hot Tub Chemistry Selector

  7. Hot Tub Chemical Damage

Hot Tub Water Conservation

Hot Tub Electrical Safety

Daily Load vs. Bather Load

If you have already read Hot Tub Chemistry Fundamentals, you know you can't treat a covered, portable hot tub like an open swimming pool.

An open swimming pool is exposed to daily contamination from dust, pollen, pollution, rain, bird droppings, bacteria, dead insects, leaves, and anything else that literally just falls out of the sky and lands in the water.

An open pool will quickly turn into a swamp unless it gets a daily dose of sanitizer to destroy all the things that contaminate the water even when you aren't swimming in the pool.

A covered, portable hot tub is more like a sealed tank or container.

A hot tub is covered most of the time so it does not accumulate a daily load of contamination unless you remove the cover and sit in the water every day. If it doesn't get dirty every day: It doesn't need a daily dose.

Overdosing sanitizer is the leading cause of
expensive chemical damage in portable hot tubs.

Most of the hot tub chemistry instructions you'll see fail to adequately explain this concept of daily load vs bather load.

This leads many hot tub owners into thinking they need to keep pouring chemistry into a covered hot tub (sealed container) on a Monday-Wednesday-Friday schedule regardless of whether or not anyone is actually soaking in the water.

Overdosing chemistry also leaves more chemical byproducts in the water. Buildup of chemical byproducts eventually causes undesireable chemical reactions which can make managing water quality difficult or impossible.

See the Hot Tub Chemical Damage page for signs and symptoms of chemical overdose.

*If you use chlorine or bromine tablets, see:
Hot Tub Chlorine/Bromine Floating Tablet Dispenser
for important instructions on managing chemical output.

Hot vs. Cold

Without a daily load from the outside environment, the biggest variable in hot tub chemistry is bather load.. The higher temperatures in a hot tub promote sweating and wash away more body oil than the cooler water of a swimming pool.

The massage action of the jets relaxes muscles but also scrubs away even more organic body stuff like bacteria, dead skin, hair and anything else that might wash away or leak out while you sit and simmer.

Warmer water also promotes bacterial growth so a hot tub can be a perfect incubator for all sorts of unpleasant microbes such as E. coli, Giardia, Hepatitis A, Legionella and Cryptosporidium.

If you have ever had food poisoning, you probably know bacteria can thrive in food if you don't store it properly.

Bacteria reproduces prolificly between 40°F and 140°F. Most hot tubs are kept at 100°F or higher. This means a hot tub can go from a sanitary soak to an itchy rash a lot faster than a swimming pool so proper sanitation is even more critical.

Hot tub heat promotes bacterial growth;
Test sanitizer level before every soak.

The heat in a hot tub is the perfect enviornmnet for unfriendly microbes to survive and thrive. Proper sanitation is critical to avoiding hot-tub-related illness and infection.

Without adequate sanitizer, hot tub water eventually turns into People Steeeew which is the perfect recipe for multiplying microbes by the millions.

See Simple Hot Tub Chemistry Checklist for step-by-step instructions on adjusting sanitizer levels.

See Hot Tub Chemistry Fundamentals for tips on avoiding the most common hot tub chemistry myths and mistakes.


The first step in keeping a hot tub sanitary is keeping unsanitary things out of the water in the first place.

A human adult hosts about 1 Trillion microbes just on the surface of our skin as part of the natural bacterial flora found on our bodies.

An ounce of soap is worth
a pound chlorine

Shower thoroughly with soap and hot water before every soak to remove as much body bacteria as possible. This also removes things like deodorant, cologne, lotions, etc. which adds to 'bather waste' and can cause cloudy water and interfere with the sanitizer's ability to kill germs.

Even after a shower, the warm water and jet action that provides hydrotherapy will scour your body and wash out every nook, cranny and crack so any remaining bacteria, oil, dead skin or other organic stuff stuck anywhere on your body ends up dissolved in the water...if you know what I mean...

Sanitize before every soak

Most people think of sanitizers as keeping the water clean between soaks but the primary purpose of maintaining a sanitizer such as chlorine or bromine in your hot tub is to kill all the germs already on your body as quickly as possible each time you slide into the water.

That's why you should always test for proper sanitizer levels and add sanitizer as needed before every soak. This helps kill any remaining bacteria on your body, prevents hot-tub-related illness and keeps the bacteria on your body from swimming down and colonizing the dark netherworld of plumbing inside your hot tub.

Once a tub becomes infected, it can be very hard to erradicate all the bacteria from all the complex plumbing hidden inside a modern, self-contained unit. If your tub has dozens of jets it also has dozens of feet of pipe connecting them all and every inch of plumbing can harbor harmful bacteria hiding behind a slime layer called bio-film.

If you have ever noticed a slimy layer on the shell of your hot tub, you can be sure the same stuff coats all the dark reaches of the plumbing and pipes. This biofilm protects bacteria from sanitizers and is often the source of ongoing water quality problems.

As an example, Cryptosporidium can survive more than 10 days in a hot tub even with chlorine maintained at 1 ppm. Individual Crypto bacteria have a hard outer shell that makes them difficult to kill in the first place. When Crypto bacteria can form a colony protected by biofilm, sanitizing the hot tub takes a deliberate effort.

The CDC recommends Hyperchlorination to Kill Cryptosporidium a process that requires maintaining 20 ppm chlorine for over 12 hours to kill 99% of the bacteria.

If a hot tub becomes infected, simple draining and refilling is not enough. The tub must be decontaminated before it can be safely refilled. Consistent use of a sanitizer such as chlorine or bromine can prevent infection and avoid the need for decontamination.

See Simple Hot Tub Chemistry Checklist for step-by-step instructions on adding and adjusting sanitizer:

You can learn more about hot tub sanitation at the Centers for Disease Control Healthy Swimming Website:


Nearly all hot tub instructions call for shocking the water on a regular basis but few instructions explain the real purpose of shocking which can lead to unsanitary conditions but, more often, leads to chemical overdose and chemical damage.

You will see terms like "shock", "oxidize" and "super-chlorinate" used interchangeably and might assume they all mean the same thing. So many products are labled as "shock" the EPA has posted the following statement from the American Chemistry Council:

"The American Chemistry Council has requested clarification of the term 'shock' on swimming pool, hot tubs, and spa labeling. Variations exist between consumers and professional groups concerning the definition of the term 'shock' as it relates to swimming pools, hot tubs and spas. The Agency considers the definition of 'shock' to imply pesticide control over microorganisms which requires FIFRA registration.'

" Claims to kill, prevent or control algae or bacteria are pesticide claims."

Read more at:

Separating the terms "shock" and "oxidize" is the first step in truly understanding how, why and when you should shock or oxidize the water in your hot tub.

Shock: kill the germs

If 'shock' means 'pesticide control' that means killing pests and, in a hot tub, that means murdering microbes by the millions.

You already know sanitizers are required in hot tub water to kill the germs already on your body but it's important to realize some of the bacteria will survive.

If normal sanitizer levels are maintained at 3 - 5 ppm, you would shock by adding enough sanitizer to raise the level to 10 ppm to ensure every microorganism is destroyed.

Shocking is the chemical process of killing any microbes that may have survived
normal sanitizer levels.

It also helps to consider the analogy of anti-biotic resistance. The first dose of antibiotics is often a high-potency 'shock' dose but if you don't take all the medication, some of the hardier microbes may survive and may develop resistance to treatment.

Shocking raises the sanitizer level high enough to kill off any microbes that have developed a tolerance to normal sanitizer levels. Without periodic shock, you can inadvertently promote a survival-of-the-fittest scenario where only the most resistant microbes get to reproduce.

Shocking kills germs.

Oxidize: burn their bodies

When you add enough santizer to kill all the germs your hot tub, the water may be sanitary but it's still full of microscopic, dead germs.

Filtration can go a long way to clearing the water but a lot of the microbes and other 'stuff' floating around in your hot tub is so tiny, it will pass right through the pores of the filter. As this microscopic debris builds up it will eventually cause your water to get dull or cloudy.

Most of this stuff is organic bather waste such as body oil, sweat and dead skin but anything you don't wash off like deodorant, cologne, lotion, etc. ends up in the water every time you take a soak.

Oxidation is the chemical process of 'burning' contamination out of the water.

Think of it like bleach in hair color or the laundry. Small amounts will lighten and brighten but too much will burn and bleach.If you pour undiluted bleach directly on your hair or a dark t-shirt, it's going to 'burn' both your folicles and your fabric.

The same process that can fry your hair and burn a t-shirt can oxidize or burn microscopic microbes and other contamination out of hot tub water.

Oxidation destroys contamination.

Super-Chlorinate: Where the confusion starts

Some products sanitize. Some products oxidize. Chlorine does both and this is where the terms shock and oxidize get tangled and most of the confusion starts.

You can shock or kill microbes by adding more chlorine and you can oxidize or burn out contaminants by adding more chlorine. The difference is the purpose.

Shocking keeps the water sanitary.
Oxidation keeps the water clear.

Shocking is done as a preventive measure; you do it before each use or on a regular basis to prevent infection.

Oxidation is a corrective measure; you do it after each use or as needed to prevent buildup of contamination.

If you are using chlorine to sanitize your hot tub, the terms 'super-chlorinate', 'shock' and 'oxidize' all mean: 'add more chlorine' so it's easy to overlook the distinction between the purpose of shocking and the purpose of oxidizing..

Non-Chlorine Shock: Where the confusion gets worse

You can pretty much bet this product is responsible for the EPA statement cited above. In fact, the EPA goes on to recommend labeling that says:

“This product is neither a sanitizer nor algicide. For control of microorganisms in pool, spa, or hot tub water, or algae control, use an EPA registered product.”

Chlorine is an EPA registered product that can both sanitize and oxidize so you might be wondering why non-chlorine shock is even needed.

When chlorine is used for both sanitation and oxidation, chlorine byproducts build up quickly and eventually cause unintended reactions that make water quality difficult to manage. In a swimming pool, for example, you might use several 40 lb buckets of chlorine in a single season.

When chlorine byproducts build up beyond a certain level, the only way to fix the problem is to drain some old water out and replace it with fresh water. In a large swimming pool that can be time consuming and costly so non-chlorine-shock can be used to avoid chlorine byproduct buildup.

Non-chlorine shock is usually a monopersulphate (MPS) compound and is just an oxidizer. If you compare it to laundry products: chlorine bleach can be used around the house as a sanitizer but non-chlorine bleach can only brighten or oxidize laundry.

MPS does not sanitize (by itself) or contribute chlorine byproducts. It only burns contamination out of the water so it might be more appropriate to think of it as Non-Chlorine Oxidizer.

Shock with chlorine.
Oxidize with non-chlorine shock.
(Warning: hot tub chemistry can make you dizzy.)

When chlorine is used as a sanitizer, the small volume of water and heavy bather load in a hot tub can cause chlorine byproducts to build up quickly. Non-chlorine shock can be used for oxidation to reduce buildup of chlorine byproducts but the benefits in a hot tub are limited.

MPS is a weaker oxidizer than Dichlor (the most common chlorine used in hot tubs) so you end up using almost 3 Tablespoons of MPS to achieve the same oxidation as 1 Tablespoon of Dichlor. This avoids buildup of chlorine byproducts but increases Total Dissolved Solids more than just chlorine alone.

When using a chlorine based system, many hot tub owners find it easier to just use chlorine for both sanitation and oxidation rather than use two separae products. They just drain and refill the tub before chlorine byproducts build up.

(See Hot Tub Refill Cost and Hot Tub Water Conservation if you have worries about wasting water.)

Bromine is a much weaker oxidizer than chlorine so non-chlorine shock is often used as a supplemental oxidizer. In bromine systems, non-chlorine shock also 'renews' or 'activates' bromine but does not, by itself, sanitize.

©Affordable Hot Tub Repair, 2014