Freshwater

The pH values in a freshwater system can fluctuate very rapidly. Even the
smallest change in pH level can really stress out your fish and make them
much more susceptible to various diseases. So keep an eye on the situation.
A pH of 5 is ten times more acidic than a pH of 6. So don’t let the little numbers
fool you — they can change your water chemistry drastically.
When you purchase your fish, make sure that your various species’ pH
requirements are compatible. Chapter 8 lists some general pH guidelines for a
number of popular freshwater species. If you are unsure, check with your local
pet dealer to find out the pH of any species you are purchasing from him.
Recall that ammonia is more toxic in a system with a higher pH.
If there are any fish in your aquarium, change the pH level gradually. Changes
of more than one range value per day (for example, from 6.5 to 7.5) can shock
your fish and result in their death.
Acidity
If, after testing, you find that the pH level of your aquarium water is too low
(that is, too acidic), you can raise it by adding sodium bicarbonate (also
known as baking soda) from the test kit or through water changes which also
remove organic build-up. This organic build-up reduces pH. If your test kit
does not have the chemicals, you can purchase them at your local pet store.
Alkalinity
If you find that the pH level of your water is too high (meaning too alkaline),
you can lower it by adding the sodium biphosphate from the test kit, or by
adding de-mineralized water. Remember that pH-lowering chemicals are
phosphate based and can encourage algae growth.
Testing Hardness (dH)
Chapter 14: The Nitrogen Cycle and Water Testing
The degree of hardness (measured by a term called degrees of hardness, or
dH) in water refers to the amount of dissolved mineral salts (mostly magnesium
and calcium) in your water. The more minerals that are present, the
harder the water. You don’t have to worry about your water’s degree of hardness
unless you live in an area where the water is very hard (150+) or very
soft (0–4). You can test for hardness by using a simple hardness test kit available
at your local fish store.
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