 Beginner FAQ: Water Treatment
Most people use tap water in their tanks; it is cheap and easy
to use. Unfortunately (for aquarists), local water companies add
chemicals to the water to make it safe to drink (e.g.,
chlorine or chloramine to kill bacteria). More recently, concern
about water flowing through older lead pipes has caused some water
utilities to add pH-raising chemicals to the water (because lead dissolves
less readily in alkaline water). Consequently, tap water must be
specially treated before it can safely be used in fish tanks.
Another potential problem concerns variability in
the chemical properties of your water supply over time (e.g.,
month-to-month). Some water districts don't have enough water
themselves, forcing them to purchase additional water from neighboring
water districts in times of shortages. If this water has a different
chemical properties (e.g., hardness),
your tap water's chemistry will vary as well.
As a common example, high bacteria levels are more of a problem in
summer than winter, especially in warmer climates. Consequently, it
is not uncommon for water companies to use more chlorine in summer
months to keep bacteria in check. Even such factors as local weather
can have an impact; heavy rains may cause the hardness of your water
supply to decrease as local reservoirs fill.
In general, chlorine and chloramine are the two additives that
cause the most problems. Note that these two substances are VERY
DIFFERENT! Be sure you know what is in your tap water and treat
appropriately.
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.
One problem with using chlorine to treat water is that it breaks down
relatively quickly. Another concern with the use of chlorine is that
it can combine with certain organics (that may or may not be present
in your water) forming trihalomethanes, a family of carcinogens.
Consequently, many water companies have switched from using chlorine
to using chloramine. Chloramine, a compound containing both chlorine
and ammonia, is much more stable than chlorine.
Chloramine poses two significant headaches for aquarists. First,
chlorine-neutralizing chemicals such as sodium thiosulfate only
neutralize the chlorine portion of the chloramine, neglecting an even
bigger problem: deadly ammonia. The consequences can be devastating to
fish. Although a tank's biological filter will (eventually) convert
the ammonia to nitrate, the time it takes to do so may be longer than
what your fish can tolerate.
The second problem relates to water changes. One of the primary
reasons for doing regular water changes is to remove nitrates that
build up. If your replacement tap water contains ammonia, you'll be
putting nitrogen right back into your tank and it will be impossible
to reduce the nitrates below the concentration in your tap
water. Fortunately, tap water concentrations are relatively low (1 or
2 ppm); you are more likely to have a much higher concentration of
nitrate in your tank.
Chloramine can be safely neutralized through such products as Amquel,
which neutralize both the ammonia and chlorine portions of the
chloramine molecules. The neutralized ammonia will still be converted
to nitrates via a biological filter.
Another method for neutralizing chloramine is to age the water while
simultaneously performing biological filtration. For example, get an
appropriately-sized (plastic) garbage can, fill it with tap water,
dechlorinate it with sodium thiosulfate, and then connect an
established biological filter to it. Just as in your tank, the bio
filter will convert the ammonia to nitrate, after which it can safely
be added to your tank. Note: you must add sodium thiosulfate to
neutralize the chlorine; otherwise, the chloramine will kill the
bacteria in your biological filter.
Alternatively, the ammonia can removed by filtering the water through
zeolite or carbon before adding it to your tank. [Note: folks report
mixed success with this. If you have concrete (positive or negative)
experience to report, please notify the FAQ maintainers.]
In addition to the additives described above
(chlorine and chloramine), municipal water may (or may not!) contain
other elements that the aquarist may need to know about. Water
in some locations actually contains nitrates. In some places, water
contains elevated concentrations of phosphates (1 ppm or more). High
phosphate has been linked to algae problems, and a comprehensive algae
control strategy may require removing phosphates. High levels of iron
(1 ppm or more) have also been linked to thread algae. Consult the
algae section of this FAQ for more details.
The quick answer is to ask someone who knows. A local fish store (if
they reside in the same water district as you do) should be able to
tell you. Alternatively, call your local water utility. Ask to speak
with the ``water chemist''. Tell them you are an aquarist and want to
know about the pH, GH, and KH of your water, as well as how much the
water characteristics vary from month to month. Finally, (in the US)
if you really want details, have them send you a copy of the periodic
water report they are required to generate for the EPA. It contains a
detailed listing of exactly what your water contains and in what
concentrations (e.g., iron, nitrates, phosphates, etc.). By law, the
report is available for public inspection.
You may have access to well water instead of municipal tap water.
One advantage with well water is that you don't need to deal
with chlorine and chloramine. On the other hand, well water is
frequently (much!) harder than water available through local
utilities. In addition, the only way to know its composition (GH, KH,
etc.) is to run tests on it yourself. Alternatively, there are
companies to which you can send water samples that will perform a
detailed analysis of its contents (for $20-100).
One potential problem with using well water is that it frequently
contains high concentrations of dissolved gases (which may be dangerous to
fish). For example, well water is frequently supersaturated with CO2,
which lowers the water's pH. Once the CO2 escapes, the pH will
increase. Fish shouldn't be subjected to this temporary pH
fluctuation. For safety, aerate well water thoroughly for several
hours before adding it to your tank.
``Cycling'' Your Tank
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