threat of chlorine poisoning from tap water has always been with the
urban Koi keeper. However, due to the demands of an ever-increasing
population, water is now delivered with a more potent disinfecting dose.
to the hobby of Koi keeping tend to think that since tap water is fine
for humans, it should be equally fine for their fish collection too. To
their dismay, they often discover that it is not the case when their Koi
suddenly becomes ill or even die, after a major water change. Chlorine
poisoning is the most likely cause. With time, the more experienced Koi
keepers learn how to cope with the chlorine threat, but now, due to the
demands of an ever-increasing population in urban areas, water from the
tap comes with a far more potent disinfecting dose.
is the responsibility of water supply authorities to ensure that all
water delivered is safe for its intended domestic use. Chlorine gas is
mostly used for this purpose. The chlorine gas combines with the water
to form hypochlorous acid (HOCl) that is one of the most effective
antibacterial agent known to man. Above pH 6,0 hypochlorous acid
dissociates into hypochloride ions (OCl-)
which is about 100 times less effective at disinfecting. At pH 8,0 all
the chlorine is in this form. The availability of these three chemicals
(chlorine gas, hypochlorous acid and hypochloride) in the water is
termed the free chlorine residual.
supply authorities like the Rand Water Board aims to deliver water to
household taps with a 0,3 to 0,8 mg/l
free chlorine content. However, while chlorine is a very
effective disinfectant, in the process it dissipates quickly leaving the
more distant delivery points of the network potentially unsafe. In order
to ensure these minimum health requirements, treatment plants deliver
water into the network with as much as 10 mg/l free chlorine.
is a costly exercise and water supply authorities are now using
chloramine in combination with chlorine as a disinfectant. Chloramine
(pronounced -mean) is an
inorganic complex that is formed when ammonia combines with chlorine in
water. Unlike chlorine, chloramine is a very stable compound that will
remain active for many days, even after being aerated or exposed to
direct sunlight. When it does break down, it dissociates into free
chlorine and ammonia. Koi keepers now do not only have to contend with
chlorine, but also with the extended potency of the chloramine and
additional ammonia, when they fill their ponds.
in the water triggers an escape response in the fish, and since they
cannot escape the confines of the pond, their stress level increases to
a point where they become exhausted and weak. They will finally stop
ventilating because of the destructive effect the chlorine has on their
gill tissue, hang motionless at the surface and die.
may have witnessed this behaviour when Koi are released into new
environments like in show display ponds if the water was not adequately
detoxified beforehand. The fish will shoal and swim energetically around
the pond. Your first reaction will be: Hey, look at this fish! They sure
are happy and alive. However, donít be fooled. Soon they will start
slowing down, and the next morning, when the show opens, and the public
rushes in, they will be either dead or looking miserable and decidedly
levels of chlorine are usually quoted as combined residual chlorine,
which represents the total free chlorine and chloramine content of the
water. A combined residual chlorine concentration of 0,3 mg/l is
sufficient to kill most fish fairly quickly, while 24 hour exposure to
levels as low as 0,04 mg/l can prove fatal. Therefore, any measurable
levels of chlorine residuals should be regarded as unsafe for fish in
the long term.
a pond is filled up with fresh tap water the fish can be exposed to high
chlorine levels for many days. The possibility of increased ammonia
levels should also not be ruled out. The chlorine could kill sufficient
bacteria in the filter, which can make it impossible for the pond system
to cope with the increased ammonia level. Chlorine and ammonia levels
can also vary considerably from time to time and from area to area,
making it difficult to adhere to a standard modus operandi when filling
ponds. (The pH of the tap water of a specific site have been seen to
vary between 7,1 and 8,7 within 5 days) Koi keepers should invest in a
chlorine test kit that will indicate the total chlorine. Kits used to
test the chlorine of swimming pool water are not adequate because they
measure free chlorine residuals only.
water typically contains 0,1 mg/l ammonia as a result of the chloramine
manufacture process. This is not too severe, but there is no guarantee
that it will not be higher sometimes. Koi keepers should therefore test
the ammonia level of their tap water as well before filling the pond.
They might well decide to postpone their water change for a few days!
proprietary products are available from pet shops and Koi dealers that
will neutralise chlorine. Sodium thiosulphate, also known as hypo or
fixer, is readily available from chemists, co-ops or photographic shops
in a crystalline (large monoclinic crystals) or anhydrous (white power)
form. An application of 7 mg/l sodium thiosulphate in the crystalline
form is required to neutralise 1 mg/l of chlorine (5,5 mg/l sodium
thiosulphate of the anhydrous form will do the same).
Pond keepers are often told that they should
de-chlorinate tap water before putting it into their pond, While this is
ideal, it is often impractical and not really essential if the exposure
to the chlorine is short-termed. The following procedure for doing water
changes is both safe and simple:
ensure some degree of dilution of the chlorine in the water one should
never do more than a 50% water change. Calculate the volume of water to
be replaced. If you do not have a residual chlorine test kit handy,
assume that the tap water contains 2 mg/l
chlorine. Dissolve in a bucket 7g sodium thiosulphate (one heaped
teaspoon) for every mg/l chlorine and for every 1000 litres of pond
water treated. (A 10,000 litre pond will require about 10 X 2 X 7 X 0,5
= 70 gram hypo for a 50% water change.) Fill the pond until it is almost
full and then slowly add the thiosulphate to the pond while using the
water jet to create a current that will ensure proper mixing.
if this is all a bit technical for you, take a walk to your nearest Koi
or pet shop and ask for their advise for some off-the-shelf remedy to
neutralise chlorine in pond water. Do make sure you buy enough for the
volume of your pond. Do make sure you follow the instructions diligently.
water changes of less than 10% should not worry the Koi keeper. The
organic matter in the pond water will greatly assist in de-chlorinating
the free chlorine while the dilution effect will render the chloramines
harmless. If thiosulphate is not used, the water should be sprayed into
the pond in a fine mist in full exposure of the sun to assist in the
decomposition of chlorine. Chloramine and ammonia will not be affected
by this treatment though and special precaution must be taken for it.
As our urban population grows,
Koi keepers can expect to have to deal with a deteriorating water
quality from their taps. Who knows what the future has in store, but
judging from the battle Koi keepers in Japan and the UK have, we should
still be quite thankful for tap water that we can both drink AND keep
our Koi in.
revised version on an article first published in KOISA, newsletter of
the South African Koi Keepers Society, December 1995, by Servaas de Kock