Daily Load vs. Bather Load
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.
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
See the Hot Tub Chemical
Damage page for signs and symptoms of chemical overdose.
*If you use chlorine or bromine tablets, see:
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
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
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
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
See Hot Tub Chemistry
Fundamentals for tips on avoiding the most common hot tub chemistry
myths and mistakes.
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
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.
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
" Claims to kill, prevent or control algae or bacteria are
Read more at: http://www.epa.gov/oppad001/shock_ltr.htm
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
'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,
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.
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.
the confusion starts
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.
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
“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
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
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.