Water chemistry basics
Water chemistry basics
I found this english text on website Mongabay.com, devoted for aquarists, but informations are equally valid for basic understanding.
PH
The pH scale is a scale which is used to measure the acidity or alkalinity of a substance. The scale ranges from 0-14, with 0 being the most acidic, and 14 being the most alkaline. Water with a neutral pH of 7.0 has an equal ratio of H+ ions to OH- ions. Water with a pH below 7.0, is considered acidic (having a more H+ ions than OH- ions), while water with a pH above 7.0 is considered alkaline or basic (having a more OH- ions than H+ ions). Almost all freshwater fish inhabit waters with a pH from 5.0-9.0, with the majority of these inhabiting water with a slightly acidic to neutral pH (6-7.5).
Lowering the pH: The pH can be lowered by using a pH-lowering chemical. Be aware that many pH-lowering products use phosphate-based chemicals. Phosphate is a nutrient that encourages algae growth. In hard water, the pH may be difficult to lower. First, soften the water by peat filtration or reverse osmosis, and then try lowering the pH.
Water Hardness
The degree of water hardness relates to the amount of dissolved minerals, especially calcium and magnesium, in the water. Water hardness is generally expressed in the amount of calcium carbonate (CaCO3). Water hardness is measured in ppm (part per million), kH (carbonate hardness), and dH (degrees of hardness) or gH (general hardness). Water is expressed as soft (having few dissolved minerals) or "hard" (having many dissolved minerals. General levels of water hardness are expressed in the table below (1 dH is equivalent to about 17 ppm).
very soft 0 to 70 ppm 0 to 4 GH (dH)
soft 70 to 135 ppm 4 to 8 GH (dH)
medium hard 135 to 200 ppm 8 to 12 GH(dH)
hard 200 to 350 ppm 12 to 20 GH (dH)
very hard over 350 ppm over 20 GH (dH)
For most aquariasts water hardness is not particularly important. However, excessively soft water can cause problems. Because softer water has less buffering capacity due to a lack of CaCO3 (a natural buffer), and is subject to pH crashes, where the pH falls dramatically causing harm to aquarium inhabitants.
Carbonate Hardness: Carbonate hardness (kH) is not used as a measurement of hardness as often. KH includes the presence of minerals and charged ions, other than Ca and Mg, dissolved in water.
Changing the Water Hardness: Water hardness can be manipulated in several ways. To make the water softer, the water can be filtered through peat moss or filtered through a reverse osmosis system. Ion exchange resins also can be used to lower the water hardness. Boiling water for a period of time can also reduce its hardness. To harden the water, filter the water through dolomite or crushed coral until the desired hardness is reached.
Electrical Conductivity: By running an electrical current through the water, the level of conductivity can be found. Conductivity indicates the amount of ions (electrically charged particles) are in the water. The higher the water hardness, the greater the conductivity. Testing the conductivity of the water only finds the total amount of ions present in the water, and does not give the origin of the ions, whether they are Mg, Ca, or Fe.
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