Anytime a pool is getting heavy use chlorine levels will drop as free chlorine
combines with contaminants and forms chloramines. Chloramines cause that heavy
“chlorine" smell any swimmer knows and loves. Though attributed to too much
chlorine it’s actually the best indicator that chlorine is way too low! The pool
needs a big dose of chlorine right away or bad things will happen. This is where
pool shock comes to the rescue. Designed to add lots of chlorine in just minutes
shock products are often the same stuff you use day to day but in a different
form. There are two kinds of shocks; chlorine based and non-chlorine. Each is
useful but in different situations.
Chlorine shock
Chlorine shock comes in three forms; calcium hypchlorite (Cal Hypo),
sodium dichlor ()Dichlor) or lithium hypochlorite(Lithium). Cal hypo and dichlor
were discussed in Part One of this series as regular sanitizers. Lithium
hypochlorite is only used as a shocking agent. In each of these products the
chlorine molecule is carried or bound to a different substance; lithium, sodium
or calcium. Lithium and sodium dissolve nicely in pool water, calcium doesn’t so
lithium and dichlor can be added directly to a pool while calcium should be
dissolved in a bucket of water before adding. If not pre-dissolved Cal Hypo will
settle to the bottom and bleach lots of nice little white spots on a vinyl
liner.
A shocking agent is meant to be a quick fix. The chlorine level
is raised to a level as high as 10 ppm (parts per million), too high for
swimming. Since unstabilized chlorine is quickly burned out by sunlight, cal
hypo and lithium are nice shock agents as they are both unstabilized. Dichlor,
however, is stabilized and will hang around for up to six hours. Dichlor is fine
but don’t plan on using the pool for a while.
Dichlor and Cal Hypo both
pack a powerful punch with 56 and 65 percent available chlorine respectively.
Lithium usually provides 35 percent and is a relatively weak sister requiring a
heavier dose for the same results.
All three shocks are available in
convenient 1 lb. pouches or in pails up to 50 lbs. Cal hypo is the cheapest and
most popular, lithium the most expensive and least used. Dichlor is mid priced
and widely available. All three types require the pool to be closed until
chlorine levels drop below 3 ppm.
Non Chlorine shock
A
relatively new development, non-chlorine shock has proved to be a popular choice
with many pool owners primarily because the pool can stay open for use even
after shock is added. Pretty cool, huh?
Sort of. Non-chlorine shock, as
one might expect, contains no chlorine. If chlorine is what a pool needs how
does this stuff do any good? The active ingredient in non-chlorine shock is
potassium monopersulfate or PMP. It has little if any oxidizing potential but it
does do something pretty neat. PMP actually frees chlorine bound up in
chloramine compounds and makes it available to sanitize again. And the pool can
stay open while this miraculous process takes place. There is a catch. Often
after prolonged summer use pool water has little or no chlorine or chloramines.
Sunlight and bather load has used up almost everything. Adding non-chlorine
shock at this point will do nothing because the PMP has nothing to work with.
Make sure to take a total chlorine reading before using non-chlorine shock. If
total chlorine is low use a shock containing chlorine.
Using Shock
Properly
-Regardless of the type used it’s best to add shock when
people are done using the pool for the day. The overnight hours are best because
unstabilized chlorine will last longer. Remember to run that filter.
-Always try to verify that shocking your pool has pushed chlorine levels
to at least 5 ppm. Lower concentrations won’t do a proper job and could lead to
trouble.
-It’s good practice to pre-dissolve shock before adding to the
pool even if it’s lithium or dichlor. Always add shock to water NOT water to
shock.
-Remember, non-chlorine shock WILL NOT WORK if chlorine levels
are too low.
Rob "Dr. Duck" Coxworth is the driving force behind http://www.webfoot leisure.com/, an
on-line retailer of swimming pools, supplies,equipment and accessories. Rob has
spent many years in the pool industry in a variety of roles; CEO, manufacturers
rep, consultant, National Sales Manager and part time pool float. Dr. Duck likes
to write about pool issues and share the information he's gained from working
with pool industry firms over the years.
Disclaimer: All information on this site is provided for informational purposes only! By no means is any
information presented herein intended to substitute for the advice provided to you by any health care or other professional
or organization.
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