What Kind of Water Should I Use on a Freshwater Fish Tank?

Naturally occurring freshwater is composed of two fundamental elements: hydrogen and oxygen. Beyond this, water conditions are variable and dependent on source (i.e., city or well water). The mineral content, pH, and metal or biological contamination of your water require close attention. The pH, or relative alkalinity or acidity of water, tells a great deal about its quality. Most freshwater fish prefer a neutral environment (pH 6.5-7.5). Water can be "hard," or low in acidity with lots of minerals, or may be "soft" and acidic. Once an appropriate pH is achieved by adding or removing minerals, an aquarist can provide plants and filtration systems to remove toxic nitrates created from the breakdown of ammonia.

Most tap water is treated to eliminate bacteria. Unfortunately, the chlorine used for treatment is toxic to fish and potentially deadly to the beneficial bacteria necessary for nitrification. Often, toxic metals like copper, mercury, or zinc found naturally in water aren't sufficiently filtered out. Water conditioners are available to detoxify chlorine and other heavy metals. Vigilance, regular testing, water changes and cleaning are key to maintaining a healthy freshwater environment.