Monday, December 23, 2013

Introduction on Chlorine & Chloramine

Dealing with Chlorine and Chloramine in Aquarium Tanks

Chlorine and chloramine are chemicals which are commonly added to tap water by water companies to make it safe for drinking.

Chlorine has been used for many years as a water disinfectant however recently many drinking water suppliers have chosen to replace chlorine with chloramine for two important reasons---first, chloramine lasts longer than chlorine, and second, it does not react with organic molecules as readily as chlorine does. The products produced by the reaction of chlorine with organic matter can be toxic to people thus using chloramines can reduce this possibility of toxicity.

In places where drinking water contains high amounts of organic molecules, chlorine tends to bind with these molecules to form trihalomethanes, which have been viewed as carcinogenic and have been implicated in several forms of cancer. If phenols are present in water, chlorine can bind with them too, giving a foul chemical taste to the tap water.

Trihalomethanes can be adsorbed by activated charcoal provided that there is slow water flow to allow sustained contact with the water. Since this is highly impractical for many water treatment facilities, many water companies choose to add chloramine to the water before it leaves the treatment plant.

For many aquarists, dealing with chloramines in tap water is definitely a challenge. As for chlorine, letting tap water sit for a few days before being used can eliminate the added chemical. In the case of chloramine, aquarists must undertake specific measures to aggressively eliminate it from tap water.

What is chlorine?

Chlorine is a chemical element that occurs as a greenish yellow gas at room temperature. Aside from being frequently used as a disinfectant in water, it is also a component in the making of chloramine. Below is a typical reaction that will occur when chlorine is dissolved in water.

Cl2 + H2O --> HOCl + H+ + Cl-

Another common practice conducted by aquarists to de-chlorinate tap water is using commercial de-chlorinators are usually plain sodium thiosulfate-based (Na2S2O3) that comes pre-mixed usually at 1% concentration with distilled water,. A few drops of the solution (about 10 drops in 10 gallons of water) can neutralize the usual levels of chlorine in tap water.

If your faucet has an aerator, it can provide all the out-gassing needed for a partial water change of your fish tank. A faucet aerator with activated carbon filter can also enhance de-chlorination particularly if you can slow the flow of water from the faucet.

What is chloramine?

Chloramine is a result of the reaction between dissolved chlorine gas (HOCl) and ammonia in tap water. In many water supplies, the predominant form of the chemical is monochloramine (water pH is 7 or above). The form of chloramine which is formed will depend on water pH, a factor which exerts an influence on the inter-conversion of ammonia (NH3) with ammonium (NH4). It is also for this reason that you should test your aquarium water regularly to ensure that the pH remains favorable for the formation of monochloramine, which is the preferred compound among the three compounds which may be formed when ammonia reacts with chlorine in water.

The stability of chloramine permits better residual disinfectant levels in the water. However, this property creates problems for aquarists since the chemical cannot be removed by simply out-gassing, just like chlorine. Even with exposure to sun and high oxygen environment, the levels of chloramine in the water can last for a week.

The amount of chloramine present in water greatly varies. The maximum amount allowed is 4 ppm-Cl. The span of time that the water has been sitting in the pipes and your distance from the treatment plant will also influence the amount of chloramine in your tap water.

Unlike chlorine, chloramine won’t easily evaporate into the surrounding air. This is the ultimate reason why water companies add it to tap water. Chloramine stay more stable in water compared to chlorine.

Testing for chloramines

In order to ensure that your water is free of toxic levels of chloramines, use a test kit that specifically indicates testing for “total chlorine” or “combined chlorine”.

It is also important to use a test kit for ammonia because tap water which is positive for ammonia indicates treatment of water with chloramines.


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