Even in water safe for humans, there are guppy toxins.
Chlorine easily dissolves in water. Water utilities use it to kill pathogens. In the U.S., the Environmental Protection Agency (EPA) specifies that drinking water contain at least 0.2 ppm (parts per million) chlorine. However, utilities in warm climates or areas that have high bacterial counts in the water may use more than this.
The further you are from the water processing plant, the less chlorine in the water, because chlorine dissipates from water quickly. However, even a minute amount of chlorine in the water can harm your guppies. Concentrations above 0.003 stress guppies. Concentrations above 0.2 can quickly kill guppies. Chlorine will dissipate from water that is rapidly aerated in 24 hours or less. This is a good reason for using a water holding tank. So-called “instant water conditioners” contain a chemical called sodium thiosulfate that neutralizes chlorine. Highly concentrated versions require only a drop in a gallon of water. However, you should not add chlorinated water to your tank of guppies and then treat it. You should treat the water first, and then add it to the tank. Common sense.
You many think that it’s okay to add 10% chlorinated water to your tank, because the chlorine content is so dilute. However, even minute quantities of this deadly chemical can damage the delicate structures of gills in your guppy. Why risk it for the few pennies chlorine neutralizers cost?
We use a product called Sea Chem Prime because it is highly concentrated, relatively inexpensive, and it treats both chlorine and chloramine.
From the water utility’s point of view, the problem with chlorine is that it breaks down and leaves the water too quickly. The more distant the house is from the plant, the less effective the water treatment. Also, when chlorine breaks down, it can combine with certain organics forming trihalomethanes, a family of carcinogens.
For many areas, chloramine, a compound containing both chlorine and ammonia, is “the solution” because it is much more stable than chlorine.
Chloramine is a disaster for guppy breeders. When it breaks down, chlorine and ammonia are the by-products. So chlorine-neutralizing chemicals only treat the chlorine, leaving the ammonia untouched. In a bare tank that has not been conditioned, the ammonia is a deadly toxic that can quickly kill fish. Even in an aged tank with a functioning biological cycle, the ammonia can overwhelm the bacteria’s ability to convert it to nitrite and then to nitrate. Eventually the stress experienced by the guppies leads to disease.
Another problem arises with water changes. One of the reasons for doing water changes is to reduce the build-up of nitrates, the end product of the biological cycle. Nitrates are not toxic at low levels, but as they build up they stress the fish. Adding ammonia that eventually converts to nitrates means that you cannot reduce the level of nitrates below that sustained by chloramine-treated water. However, the level of nitrate that results from the biological cycle acting on the ammonia component of chloramine is very low. It does mean, though, that you will have to be more aware of the nitrate levels in your tanks.
There are water conditioners that neutralize chloramine, such as Amquel and Seachem Prime. However, the neutralized ammonia component of chloramine is still converted to nitrate by bacteria.
Other Minerals in Water
Your water supply may contain other chemicals, some which benefit guppies, others that are harmful.
Phosphate and Nitrate
Check your water for elevated concentrations of phosphates (1 ppm or more). Phosphate is a component in algae blooms in the tank. Nitrate is a nutrient for plants, and algae are plants!
Iron, Copper, Zinc, Manganese, Iodine
Many minerals are beneficial to guppies in low concentrations, and toxic at high concentrations. To see a list of these minerals, consult the nutritional table on Tools and Table section of this site.
Copper is a special problem. Water standing in copper pipes in your house may contain high levels of copper. Hot water dissolves copper more readily, so measure hot water separately from cold water. Let the faucet run for a couple of minutes before water changes. If your water is acidic coming out of the tap, it may contain high levels of copper, since acidic water dissolves copper and other minerals more readily than hard water.