The chlorine ion dissolved in water is hypochlorite
(Cl2O2), the same ion as found in regular household
chlorine bleach like Clorox. No anion without
a cation, so hypochlorite comes to you as
sodium hypochlorite. When a solution of chlorine
bleach in water has entirely dried, there's
no residue but a bit of common salt (taste
it and see), which you might want to rinse
away.
Water utilities have replaced
hazardous chlorine
gas (Cl2), which used to be shipped around the country
in railroad tank cars, either with chlorine
produced on-site by the electrolysis of salt
brine, or with dry calcium or sodium hypochlorite.
If the chemistry of chlorine is mysterious
and you want some basic introduction to the
science of chlorine, its manufacture and
its everyday uses, the Chlorine Chemistry Council website offers some material, including some more
specialized studies and discussion (from
the chlorine manufacturers' point-of-view
of course) of some public policy issues.
AquaScience Research Group, manufacturers of a dechlorinator for aquaculture,
offer another good discussion of the water
chemistry of chlorine and chloramines at
Dechlorinating it is often the first concern with tapwater.
Most commercial dechlorinators are based
on plain sodium thiosulfate, Na2S2O3, a crystalline salt that generally comes
pre-mixed with distilled water, usually in
a 1% solution. At this strength, 10 drops
(that's 0.5 cubic mm) will neutralize common
municipal levels of chlorine in 10 gallons,
turning the chlorine to harmless chloride
ions and adding some molecules of sodium
and sulfur to the water. Unreacted
sodium thiosulfate that may be left over
is pretty inert and harmless.
Two commercial brands that are plain
sodium thiosulfate are Wardley's ChlorOut
and Mardel's MarChlor.
If you needed large quantities of chlorine
neutralizer, you could buy sodium thiosulfate
less expensively in crystal form, directly
from a manufacturer, such as Fishy Farmacy. Doc Johnson tells you how to mix up a stock
solution at www.koivet.com in the "Medications" articles,
under "Dechlorinator." Better get
together with a few friends, because just
1 gram of crystals in distilled water makes
a liter of 1% stock solution. At rates of
one drop of stock solution to a gallon or
two of chlorinated tapwater, that could be
a lifetime's supply.
There are also sources outside the aquarium
hobby, for sodium thiosulfate has other uses.
It keeps down extraneous bacteria in the
making of red wines; in contact with the
acids in grape juice it forms sulfur dioxide.
So, if you want to save money on chlorine
"remover" you might want to buy
it as a wine-making supply. Or as an antidote
kit for cyanide poisoning, by the way! Back
when amateur photographers were developing
their own b/w photos, sodium thiosulfate
was their "developer," and so it
was cheaply available as "hypo"
in any photo hobby shop. "Hypo"
was short for "hyposulfite of soda"
an obsolete term for Na2S2O3 . Nowadays fixatives often have additional
hardening agents to toughen the coating in
which the reactive silver emulsion is imbedded
on the photographic paper. In other words,
hypo isn't always pure sodium thiosulfate
any more, so check before you use hypo as
a good cheap substitute. Doc Johnson doesn't
recommend it.
Before municipal water utilities in the U.S.
were switching over to chloramines, I'd have
suggested that you just let chlorine outgas
naturally. I'm currently still able to do
this with New York City's vaunted tapwater.
The natural way to dechlorinate is to let
the tapwater stand for twenty-four hours
in jugs that offer a large water-to-air surface.
I like the 6-gallon unbreakable plastic jugs
Poland Spring water was delivered in til
recently; they're built to be easy to grip
and they're rectangular to stash close. But
you might need a virgin 55gal garbage can,
which you have indelibly marked in big letters
"Aquarium Use Only So Dont Even Think About
It." Either way, the chlorine will dissipate.
Frankly, if you have an aerator attached
to your faucet, it may provide
all the outgassing that's needed for a partial
water change; after all, many people are
using Python-type water-change hoses without
trouble. And if the faucet aerator is charged
with an activated carbon filter to improve
the drinking water, so much the better! Fresh
carbon will adsorb chlorine.
If you are impatient you
could run an airline
in the jug or can, but
there isn't any reason
to use de-chlorinator to
neutralize chlorine
(not chloramine), except
in an emergency.
Don't let anyone undermine
your security
about this fact. If you
have any lingering
doubts, borrow someone's
chlorine test kit
(don't buy one yourself)
and test your water.
Test the water that has
passed through your
faucet aerator. And test
the water first
from the tap and again
after sitting still
for twenty-four hours.
If you insist on owning
your very own chlorine
test, by all means
get it at the Swimming
Pool Supplies section
of your Home Depot. It's
the very same test,
using the very same chemicals,
as ones that
are specially packaged
and specially priced
for the "captive"
aquarium market.
Chloramines.
Chloramines offer a more aggressive treatment
for maintaining some residual chlorine in
tapwater. Chloramine remains more stable
in the water mains than chlorine.
In areas where organic molecules in drinking
water are high, chlorine tends to bind with
them, even such harmless ones as humic or
fulvic acids, to form trihalomethanes, which
are implicated in cancer. Chlorine will bind
with phenols too, if they are present, to
give a foul chemical taste. Trihalomethanes
could simply be adsorbed by activated charcoal
at the water plant, according to the McGraw-Hill
Encyclopedia of Science and Technology, "Water Treatment." But in order
to be effective, activated carbon needs a
slow flow that offers sustained contact with
the water and frequent reactivation in a
kiln. On the giant scale that's required,
carbon filtration isn't practical. So instead,
water boards are increasingly adding chloramines
before water leaves the treatment plant,
acting under pressure from the E.P.A. who
lowered permissible standards for trihalomethanes
in Nov 1998. "Chloramine is formed when
ammonia is added to water that contains free
chlorine. Depending upon the pH and the amount
of ammonia, ammonia reacts to form one of
three chloramine compounds. Of the three,
monochloramine is the preferred compound."
So says the Washington Aqueduct Chloramine Facts part of the DC Health website.
Because the chloramines are much more stable
than chlorine, they maintain better residual
disinfectant levels in the water mains. The
stability of chloramine creates problems
for fishkeepers, since these chemicals will
not simply outgas in a holding can, the way
chlorine does. Even exposed to sun and plentiful
oxygen, Chloramine-T could still last for
as long as a week.
My understanding of the DC Health site's
quote is that some chloramines
could as readily
form in aquarium water
if you were to add
chlorinated water straight
from the tap to
a tank that already carried
some free ammonia.
Which chloramine formed
would depend on the
pH of the water, a factor
which controls
the interconversion of
ammonia (NH3) with ammonium
(NH4). Chloramine
formation could only become an
issue if you were using a "direct-fill"
hose, and had highly-chlorinated tapwater
and free ammonia in the tank.
Chloramine toxicity. Chlorine
is an oxidizer, which burns a fishes'
gills. Chloramines, on the other hand, pass
across the gills of a fish and into its blood,
where the molecule attaches to the hemoglobin,
acting like nitrite
to induce methemoglobinemia. The toxicity of chloramines is affected
by pH, I'm reading at www.fishdoc.co.uk, with Chloramine-T more toxic at lower pH.
Fish stricken by chloramine poisoning are
sluggish and respire heavily. But chloramines
have been inflated into a bugaboo by some
packagers/distributors of various water "conditioners."
Aquarium Pharmaceuticals, for instance, characterizes
chloramine as "deadly" in corporate
literature. Nevertheless, the not-invariably-"deadly"
Chloramine-T is currently being studied by
the U.S. government as potentially important
to fish hatcheries in controlling bacterial gill disease. Studies at UC Davis have inspired widespread
use of Chloramine-T to kill pathogenic bacteria
and parasites in koi ponds. A professional
assessment I trust is this from John P. Grazek:
"The addition of sodium thiosulfate will neutralize both chlorine
and chloramine. However, ammonia is released when the sodium
thiosulfate combines with the chloramines,
and this could be a problem to fish where
there is little or no biological filtration."
(in Aquariology: Fish Diseases and Water Chemistry, Tetra Press 1992). In chloramine, two chloride ions are bound to each ammonia
molecule, and that's why you're usually advised
to double the quantity of sodium thiosulfate
you'd use for chlorine alone. In acidic water,
the ammonia released would largely be ionized
to its non-toxic form, ammonium. In a planted
aquarium NH3/NH4 would be rapidly scavenged by the plants.
Chuck Gadd's clear and succinct article on
ways you can deal with chlorine/chloramines
is at Chuck's Planted Aquarium Pages.
Testing for chloramines.
If you're testing for chloramines,
make
sure the test kit you've
borrowed is testing
for "total chlorine"
or "combined
chlorine," not for
"free chlorine."
A test for "free chlorine"
would
misleadingly read zero
in chloraminated water.
On the other hand, when
your tapwater tests
positive for ammonia, this
is a sign that
your water is being treated
with chloramines.
The Washington DC water utility offers a
document "How the conversion to Chloramines affects
your fish" generated by the U.S. Army Corps of
Engineers, which injects a note of sobriety
into this sometimes panic-inducing situation.
Being a public agency, the Washington Aqueduct
couldn't recommend any commercial brand,
but in general they recommended four general
methods for neutralizing chloramines: 1.
activated carbon in filtration, 2. sodium
thiosulfate, 3. commerically-available de-chloramination
products ("some simply remove the chlorine,
while others 'lock up' or detoxify remaining
ammonia"), or 4. a chemical agent plus
a biological agent ("bio-filter")
to remove the ammonia. (You should already
have known all this, eh?)
If you're depending on 1. filtration with
granular activated carbon to break the chloramine
bond, make sure the carbon is fresh and the filtration is slow. Since some ammonia
is likely to be freed, one way or the other,
you have an additional incentive to de-chloraminate
before you add water to the aquarium.
If you're de-chloraminating as in 3. with
commercial products, it's useful to know
that Ammo-Lock2 (Aquarium Pharmaceuticals)
and AmQuel (Kordon) each react with the ammonia
to form non-toxic, inert, moderately stable
substances. With these products, the ammonia
is bound, but not actually removed. It does
remain available to the nitrifying bacteria,
I understand; that's an important consideration.
Each company presents a clear un-hyped analysis
of its product, Kordon at www.kordon.com and Aquarium Pharmaceuticals at www.aquariumpharm.com