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What is Chloramine and Why to Test Levels of Chloramine in Fish Tanks

Brief Description

This page explains what is chloramine, answers why it's extremely dangerous for fish, and describes simple ways how to get rid of chloramine-related problems in a fish tank. You're welcome to share your experiences at the bottom of this page!


Fish keepers are presented with many problems to keep their aquariums healthy and the water quality high, many of these are from diseases and viruses that enter the tank affecting the fish but one problem that constantly needs to be kept in check is man made and its something that every fish keepers has to deal with every time a water change is performed or a tank is filled for the first time.

Chloramine is a killer of fish but it is added to our mains water to disinfect the water supply and prevent us from getting diseases and to keep the water pipe work clean. At one time chlorine was added to the mains supply and this is not such a problem to deal with, just filling a bucket and leaving it to stand for a couple of days would guarantee that the chlorine was dispersed through gaseous exchange but this does not work with Chloramine.

What is chloramine?

But what is Chloramine and how does it affect the fish, well basically it is a result of chlorine reacting with ammonia, both of these deadly to fish to produce a durable compound that doesn’t dissipate in air. The water suppliers prefer to use this nowadays as it is far more effective as a disinfectant compared to chlorine and longer lasting, hence the problems it causes fish keepers. To make life even more confusing a different compound is formed when the pH of the water is above 7.0, monochloramine is formed which is even more toxic to fish, this is why tanks that use alkalinic water have more problems with chlorine and Chloramine than tanks that have soft, acidic water. We have to resort to adding water conditioners that can combat the effect of the Chloramine and make it safe for the livestock in our tanks.

It's toxic

The Chloramine is toxic to the fish as it passes through their gills and is absorbed into the blood stream, once in there it reacts with the haemoglobin to change this to methemoglobin which is not capable of absorbing oxygen to the same extent as the original haemoglobin. The end result is that the fish struggle to maintain their oxygen levels and can be seen gasping at the water surface, much the same as if the water wasn’t aerated properly in the first place so even adding an airline is useless in this case. The only way to deal with this problem is to treat the water before it enters the aquarium and make it safe for the tank inhabitants. The level of Chloramine in the aquarium can be tested and there are testing kits available for use in the home, investing in one of these is a wise purchase for peace of mind and to ensure that we are controlling the problem properly. The information that we need is what is a safe level of Chloramine for the fish and invertebrates in the aquarium and recently there have been countless studies undertaken to research this and it is only lately that the results have been published to help us with our quest.


It has been estimated that the safe level of Chloramine for aquatic life is somewhere between 0.002 ppm and 0.005 ppm, anything above this can be toxic especially if your tank inhabitants are exposed to higher levels daily.

There are a few testing kits available for use to check the levels in your aquarium, Microbe-Lift produce a kit that uses test strips, these will also test for chlorine in the water, this is something you should always check for when purchasing your test kit, the need to test for both chlorine and Chloramine.

Details for the test strips can be found at, each kit will cost you $15.00 which equates to approx. £10.00 dependant on exchange rates and for this you get a pack of 50 test strips.

Another more well known brand is Jungle Labs who supply a testing kit for chlorine and Chloramine for as little as $6.00 (£4.00), these are quick dip test strips that should give an accurate reading after 15 seconds, for this price you get a pack of 25 strips.

How can I stop Chloramine entering my Aquarium Water?

There are basically two main methods for making your mains water safe for aquatic life, the first is by using a water conditioner, the second is to purchase a water purifier which is often more economical if you are using a high volume of water.

Water conditioners are fine in their own right but what you have to remember is that in more cases than not they do not remove the chlorine or Chloramine but they lock it so that the toxicity cannot affect the aquarium inhabitants, the only way to remove them when using these products is during the water changes. All water conditioners available will have instructions on the label as to how much to add to the volume of water that you are using, this must be followed accurately for them to be effective. I have always found the most effective conditioner to use is Seachem Prime but that is personal choice, many fish keepers will have their own preferences. Prime is initially quite expensive, about £20.00 for a 250ml bottle but only a small amount is required each time and one bottle can last for months. There are many popular brands such as Amquel, tetra Aqua Safe, Ammo Lock and suchlike that do the same thing but like the testing kits ensure that any conditioner you use can also deal with Chloramines.

Water purifiers such as Reverse Osmosis units, HMA units and DI Resin units are now readily available to remove Chloramines before any water reaches the consumer. These are good value if you require large water changes as it would be too expensive to keep using water conditioners and they work by running the mains water through a series of pre-filters, each pre-filter removing different impurities. The Reverse Osmosis and HMA units will always have a pre-filter that contains carbon which absorbs the Chloramines but these do need replacing every 6 months to be effective as the carbon will become saturated and start to leach back the toxins into the water.

Some of the above information may seem a bit complicated and time consuming to perform but Chloramine is a killer to aquatic life and without taking the necessary steps to reduce it or even remove it completely you will be putting your livestock at risk. Never add mains water straight to your aquarium without treating it first!

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