Description
This article is from the Beginning
Fishkeeping FAQ, by Thomas Narten with numerous contributions
by others.
23 Chlorine
In the US, EPA guidelines require that tap water at any faucet contain
a minimal chlorine concentration of 0.2 ppm, and stringently limits
the concentration of bacteria (which may require more than 0.2 ppm
chlorine to keep in check). Because chlorine breaks down over time,
the chlorine concentration of the water that comes out of your tap
will be lower than that put in at water plant. Thus, the exact
concentration at your faucet depends on how far you are from the water
plant, how long it takes the water to travel from the water plant to
your house, how much chlorine is initially added, etc.
Chlorine at high concentrations is toxic to fish; at lower
concentrations, it stresses fish by damaging their gills.
Concentrations of as little as 0.2-0.3 ppm kill most fish fairly
rapidly. To prevent stress, concentrations as low as 0.003 ppm may be
required. Fortunately, chlorine can easily be removed from water by
the chemical sodium thiosulfate, readily available at fish stores
under various brands. Sodium thiosulfate neutralizes chlorine
instantly. Note that there are many ``water treatment'' products that
are advertised as ``making tap water safe''. Read labels carefully.
Inevitably, the ones that neutralize chlorine all contain sodium
thiosulfate, plus other substances that may or may not be useful. If
your water only contains chlorine (as opposed to chloramine), sodium
thiosulfate is all you need. The most cost-effective treatments use
only 1 drop per gallon of water. Most other water treatments are much
more expensive in the long-term; they may require a teaspoon of
treatment (or more) per gallon!
Chlorine is relatively unstable in water, escaping to the atmosphere
on its own. Water left in a bucket (or tank) with adequate water
circulation (e.g. filter or airstone) will be free of chlorine in 24
hours or less.
Many netters report that they perform partial water changes without
ever treating their tap water to remove chlorine. Keep in mind that
even though fish show no APPARENT ill effects from untreated water,
that doesn't mean that the chlorine isn't stressing your fish. How
much stress depends on how much chlorine is introduced to the tank,
which depends on many factors (including the percentage of new water
added). Because chlorine removers are so cheap (pennies per usage),
the insurance they provide should not be passed up.
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aquaria, fish, acquarium, tank, fishkeeping
