What You Need to Know About Water Chemistry, and Why

Water in nature is rarely pure in the ``distilled water'' sense; it contains dissolved salts, buffers, nutrients, etc., with exact concentrations dependent on local conditions. Fish (and plants) have evolved over millions of years to the specific water conditions in their native habitats and may be unable to survive in significantly different environments. Beginners (especially the lazy) should take the easy approach of selecting fish whose needs match the qualities of their normal tap water. Alternatively, an advanced (and energetic!) aquarist can change the water characteristics to match the fish's needs, though doing so is almost always more difficult than first appears. In either case, you need to know enough about water chemistry to ensure that the water in your tank has the right properties for the fish you are keeping. Water has four measurable properties that are commonly used to characterize its chemistry. They are pH, buffering capacity, general hardness and salinity. In addition, there are several nutrients and trace elements.