Some Basic Water Chemistry
by Tracy Hardy
From "Fins & Friends" Regina Aquarium Society, Canada
Aquarticles
Water hardness
Most water contains calcium and magnesium in varying amounts. Most importantly are calcium
bicarbonate and calcium sulfates. Water that is rich in calcium salts is considered "
hard ", with little calcium salts it's considered "soft ". Hardness is
measured in degrees of hardness; one degree is equal to 10mg. of calcium or magnesium
oxide per litre of water.
Hardness that is caused by calcium bicarbonate is called temporary, or sometimes called
transient hardness because it disappears when the water is boiled. Hardness caused by
calcium sulfate is considered permanent because it remains after boiling. The mixture of
temporary and permanent hardness produces overall or total hardness.
DEGREES OF HARDNESS
0-4 dGH = very soft 4-8 dGH = soft 8-12 dGH= medium hard 12-18 dGH = fairly hard 18-30
dGH = hard over 30 dGH = very hard
dGH - German Total Hardness
(* Regina's water hardness is approx. 35dGH.)
Carbon dioxide
Small quantities of carbonic acids are formed quite readily by carbon dioxide dissolving
in water. The availability and amount of carbon dioxide present to be absorbed by plants
depends on the complex system of aqueous carbonic acid and carbonates.
Carbon dioxide is about 40 times more soluble in water than oxygen, but leaves water
10,000 times less easily from water than air. Approx. 0.2% of dissolved carbon dioxide is
converted to carbonic acid. When you add carbon dioxide the amount of carbonic acid
increases and the PH level drops. When carbon dioxide is removed the PH level rises.
There is a close relationship with the carbonate system/hardness and PH values.
Generally speaking the higher the hardness, the higher the PH value, but the PH seems to
be easier to stabilize in hard water.
pH values
pH values are the degrees of acidity in water when there is a change from the chemical
neutral point. When water is considered neutral there are equal parts of hydrogen ions and
hydroxide ions. The hydrogen ions make water more acidic and the hydroxide ions make water
more alkaline. Neutral water is considered 7.0, pH values above 7.0 means increasing
alkaline water, below 7.0 means increasing acidic water.
One unit in pH equals a ten times change in acidity or alkalinity. Two units means 100
times change, 3 units is 1000 times and so on.
The majority of fish prefer a pH between 6.0 -7.5.
(* Regina's water has a pH of 7.5-7.8.)
The nitrogen cycle
The pH value will determine if toxic ammonia or toxic ammonium will be produced by the
first stage of the nitrogen cycle. Ammonia happens at a pH of 7.0 and higher. Ammonium
happens at under a pH of 7.0. Ammonia can't build up in even the slightest acidic water.
The majority of plants use nitrates.
The 2nd stage is nitrite which is the result of bacterial oxidation of ammonia and
ammonium. That bacteria's name is Nitrosomonas sp. Nitrite is very poisonous to
fish. Most fish can tolerate higher levels of toxic ammonia than of nitrites.
The final stage is Nitrobacter bacteria converts nitrites to nitrates, which are far
less toxic.
The success of the Nitrogen cycle depends on oxygen. If oxygen is in low levels in your
tank, organic decay is slower and your water will have increased interim toxic products of
ammonia and nitrites.
Reference and Credits:
Baensch Aquarium Atlas (Volume 1), Dr. Rudiger Riehl/Hans A. Baensch. (1991).
ISBN 3-88244-050-3. Distributed by Rolf C. Hagen. Printed in Hong Kong. Publisher: Hans A.
Baensch- Melle, W.Germany
* David J. Claude Current RAS President ( 2001 ) and Resident all around fish expert!
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