Our Privacy/Cookie Policy contains detailed information about the types of cookies & related technology on our site, and some ways to opt out. By using the site, you agree to the uses of cookies and other technology as outlined in our Policy, and to our Terms of Use.


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

i Justin Sullivan/Getty Images News/Getty Images

One of the most important aspects of a freshwater fish tank is the water itself. Freshwater tanks require less maintenance and regulation than saltwater aquariums, but with variations in tap water occurring both naturally and through water treatment, optimal aquarium conditions may require further effort on your part.

Maintaining High Quality Freshwater

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.