water treatments






Author: Dr. L.E. Freese

What is chloramine?
How do I know if there is chloramine in my tapwater?
Is chloramine dangerous to my fish?
How can I remove the chloramine in tapwater?


What is chloramine?

Chloramine (NH2Cl) is a compound that is formed when chlorine and ammonia combine in water. The ratio normally is 1 part ammonia to 5 parts chlorine.

Chloramine is also formed if the water supply is treated with sodium hypochlorite powder instead of chlorine gas.

It is used in certain areas to kill bacteria in tap water instead of chlorine. This is due to certain factors:

  • Chlorine forms trihalomethanes (THM)
  • Chloramine stays in the water for much longer than chlorine
  • No unpleasant odour or taste

The problem with this is:

  • Need higher levels of chloramine than chlorine
  • Chloramine is stable and very difficult to get rid of

How do I know if there is chloramine in my tapwater?

The best way to find out is to phone your water supplier and ask them what is used to treat your water and if chloramines are present.

Is chloramine dangerous to my fish?

Yes, Chloramine is very toxic for fish and other aquatic life forms.

Chloramine acts differently to chlorine in that it causes little damage to the gills but passes through the membrane and into the bloodstream. Here it binds to the iron in the haemoglobin in the red blood cells. This prevents the blood from carrying oxygen and this leads to a disease known as methemoglobinemia, similar to nitrite toxicity. This causes the fish to become very lethargic and eventually they die.

How can I remove the chloramine in tapwater?

As chloramine is very stable and does not dissipate easily from the water, even with heavy aeration. If this is the method that you want to use, then the water must be exposed to sunlight and aerated for at least a week.

The chloramine compound can be broken by having very low flow rates (5-10 min contact time) through activated carbon followed by mineral zeolite media to remove the ammonia. This poses the problem of who has a mechanism where the contact time is this long and before the water reaches the aquarium? When using this method, one must ensure that the activated carbon and the zeolite are new enough for the chemical reactions to be able to take place.

RO (Reverse osmosis) does not remove chloramine, as the chloramine is able to pass through the permeable membranes just s it can pass through the membranes of the fish’s gills.

Anti-Chlorine destroys the chlorine and ammonia bond and removes the chlorine. The nitrifying bacteria in the established biofilter will remove the resultant ammonia. Therefore it is not advisable to clean the filter and do a water change of greater than 10% at the same time.   


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