Ask A Scientist© Chemistry Archive

name         Donna C.
status       student
age          30s

Question -   My friend has children and plans on using BLEACH instead
of chlorine in the pool. Is this BAD? I really don't think this is a good
idea, considering the warnings on the bleach bottle.
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Pool chlorine treatment chemicals come in two forms, one is a slow release
organic compound, the other is some form of sodium or calcium hypochlorite.
The active ingredient in all of these treatments is the same the
hypochlorite ion OCl(-1). There should be no danger as long as the water is
tested for the proper concentration.

The warnings on the bleach bottle refer to the bleach at the concentration
IN THE BOTTLE, which is about 5%, much higher than would be present in a
swimming pool provided the bleach is properly mixed after its addition to
the pool.

Vince Calder
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The sodium hypochlorite would be okay to add to the
pool. The hypochlorite will generate free chlorine as a
disenfecting agent.   The caution is that one has to
make sure that one is adding the right proportion of
chlorine.  Remember that house hold bleach may only be
7% NaOCl by weight or volume.

Sincerely, Bob Trach
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It is really about the same thing.  Bleach is sodium hypochlorite, NaOCl.
Most pools do not use chlorine directly;  those that do need to stabilize the
chlorine to keep it dissolved in the water.  This involves reacting the
chlorine with base to generate hypochlorite, which is already done in the
manufacture of bleach.  Most home swimming pools use calcium hypochlorite
(Ca(OH)2), otherwise known as HTH, as a chlorinating agent.  It works about
the same as sodium hypochlorite, but it is less soluble, so it is harder to
over-chlorinate the pool.

Both sodium and calcium hypochlorite are much safer to handle than gaseous
chlorine.  If you think the warnings on a bleach bottle are scary, you
should check out a material safety data sheet for chlorine gas.

Richard E. Barrans Jr., Ph.D.
Assistant Director
PG Research Foundation, Darien, Illinois
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