Freshwater

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Part III: Water, Chemicals, and Plants
Some fish like to live in slightly hard water, and others don’t. If you have one
in very hard water that is supposed to live in soft water, it can lead to illness
and death.
One way to dilute hardness is to add rain or distilled water to your tank.
Another way is to boil the water and let it cool before adding it to your tank.
Both methods lower the pH levels. Extreme hardness is found in alkaline
(high pH) waters. Reverse osmosis units soften aquarium water, but these
units tend to be expensive and use a lot of tap water in order to produce a
small amount of mineral-free water.
You can also use a water softener or add peat moss to your filter (boil the
peat first to remove any unwanted organisms). Hardness can be easily
increased by adding sodium bicarbonate in small amounts at a time (about a
teaspoon per 55 gallons) and then monitoring the change.
During the conditioning period, closely monitor pH, ammonia, nitrite, and
nitrate levels using standard test kits. Take daily readings. The pH level goes
down as a normal part of the conditioning process. You can raise it again
through frequent water changes if you live in an area with harder water (hard
water and high alkaline levels go together). Allowing the pH to decrease over
a long period of time during the conditioning process keeps helpful bacteria
from multiplying to its full potential. When nitrite and nitrate levels begin to
overstep their limits, daily water changes help alleviate that problem.
Do not use an excess amount of chemicals or medications during the conditioning
period because they can potentially damage bacterial growth.
When the conditioning process is complete, you can begin adding a few fish
every week to allow the bacteria bed to increase at a normal rate. If you make
the mistake of immediately overstocking your aquarium, ammonia levels
(ammonia spikes) will gradually build up. To correct this situation, reduce
the number of fish in the tank or add more filtration.
There you have it, the basics of aquarium water. With test kits you can always
be on top of the situation and provide your fish with water to match their
needs.