Treating the Treated – The Line Between Tap Water and Aquarium Water

A few hundred years ago, people in Western cultures like 16th century England often drank very little water. Because of untreated sewage draining into water sources and contamination in rivers, other beverages like beer and wine were actually preferred as safer choices. As technology and our understanding of health and technology advanced, we came up with more ways to purify our water sources. At the start of the start of the 19th century, a scientist named William Cumberland Cruikshank found that chlorine would purify water by killing microbes and bacteria like the notorious E. coli. Chlorine is still used in most developed countries to make drinking water safe and chloramine, a combination of chlorine and ammonia is starting to overtake even this old standard.

So, why the history lesson in an aquarium blog? What does this mean for us? It means that almost all municipal water sources in the United States are now regulated by the Environmental Protection Agency and will contain chlorine and/or chloramine to kill bacteria – good for us, but bad for our aquariums since chlorine and chloramine are toxic to fish and other aquatic organisms. Understanding how to get rid of these chemicals before adding it to your aquarium can be the difference between life and death, for your aquarium anyway.

Chlorine (Cl2) was one of the first methods used to purify water. It can be added to water as a gas or a liquid. It is often used in many disinfectant cleaners and the ever-popular chlorine bleaches. Chlorine is very effective in killing microbes and bacteria, but it isn’t very stable and doesn’t last long. In fact, water treated with just chlorine can be “out-gased” just by letting it sit with some simple aeration for a day or so (a small pump or airstone will usually work, and a small fan on the surface of the water will help break up surface tension to let the gases escape faster). This instability happens to be what is making it defunct in many municipalities. Most of the chlorine is out-gased soon after it leaves the treatment plant as it runs through pipes. The water is usually clean by then, but any contamination in the pipes can foul the water again. To compensate, some areas add more chlorine in the hopes that it will last longer, leading to the bleach-like smell or taste that is sometimes left if the concentrations were high or if the tap in question is close to the treatment source.

Chloramine (NH2Cl) is a compound of chlorine (Cl2) and ammonia (NH3). Most aquarists are already well aware of ammonia and its toxic consequences but in this case it creates a very stable compound for water treatment. While chlorine out-gases relatively quickly, chloramine remains in the water for much longer. A specialized filter or chemical neutralizer may be required to remove it before the water can be used in an aquarium. Some tap water filters may remove chloramine while some may only remove chlorine.

There are countless water conditioners available on the market for aquarists. It is important to know which one is right for you. True dechlorinators only neutralize chlorine. If your water is treated with chloramine, the ammonia will be left behind and can lead to an ammonia spike in the aquarium. While the ammonia is bound into the chloramine compound, it will not register on most aquarium ammonia tests but will “appear” once the chlorine has been neutralized. Water conditions that neutralize chloramines will bind the chlorine and ammonia separately. Once the chlorine and ammonia are separated by these conditioners, the chlorine can easily be neutralized or outgassed. The ammonia is still left behind. It may be “de-toxed”, but its a bit like putting a scabbard over the blade of the knife – the dangerous part is still there, but it can’t do much harm at the moment. Eventually, the biological filtration in the tank will convert this ammonia to nitrite and then to nitrate just like it does to the ammonia from fish waste and food.

If you use municipal water (as opposed to well water, usually in more rural areas), your water must be “dechlorinated” before you add it to your tank for water changes, top-offs, or new aquariums. In order to choose the correct “dechlorinator” or water conditioner for your tank, you have to know if your water is treated with chlorine or chloramine. You can contact your municipal water source and let them know that you are an aquarist and need this information or you can refer to the Environmental Protection Agency’s website where some localities have their information published. Your local pet stores may also be able to provide you with this information if you are on the same water source.

For more information, visit the US Environmental Protection Agency’s Ground Water and Drinking Water website or their Frequently Asked Questions (FAQs) page.