What is Chlorine?

Chlorine is a water additive found in tap water. Chlorine destroys bacteria and organic pollutants; thereby, making tap water safe for human consumption. This is all well and good, but chlorine is also highly toxic for your fish, not to mention your nitrifying bacteria colony (biological filter). Chlorine damages a fish's gills and skin. Symptoms of chlorine exposure are erratic swimming, gasping at surface, and erratic respiration.

Tap water should never be added directly into your aquarium without treating first for chlorine. Chlorine can be very simply removed from tap water with the use of a dechlorinator. There are many brands of dechlorinators in the market today. Choose a dechlorinator which treats for both chlorine and chloramine. Chloramine is a more stable form of chlorine, a "time-release" chlorine, if you will. Chloramine is an additive commonly found in tap water which is also harmful to your fish.

An alternative to using a dechlorinator is "aging your water". To age your tap water, fill a container with tap water and leave it to sit overnight. Chlorine is relatively unstable and will dissipate readily through aeration. Aging your water has the added benefit of not only removing harmful chlorine, but ensuring that the water has time to acclimate to room temperature. Thus when you add the "aged water" to your aquarium, you won't expose your fish to temperature shock.

*Note*, however, that aging your water overnight does not rid your tap water of chloramine (verify whether your local water supplies have a chloramine additive). Chloramine is much more stable than chlorine and simple aeration will not suffice, in which case, it is best to use a dechlorinator that treats for both chlorine and chloramine.

Optimum level of Chlorine/Chloramine: 0 ppm

Removal: Dechlorinator, Aging of Water (Aeration)