Chloramines – Simplified
Dougall Stewart BSc.
UK Discus Association Founder
Monochloramine (NH2Cl) is an inorganic
chloramine that is commonly added to tap water by local water authorities.
It is a disinfectant agent that is added at approximate concentrations of
1.5-2.5mg/l in the UK. However depending on the amount of ammonia to
chlorine present and the pH of the water that the products are added to,
other inorganic chloramines may form e,g, dichloramine (NHCl2)
and or trichloramine NCl3.
Simplified equations for the reaction
between ammonia and chlorine:
If the ratio of chlorine to ammonia is 3-5:1 then
monochloramine and hydrochloric acid are formed. However, as the pH of the
solution drops below neutral and more chlorine is added, there is a greater
tendency for dichloramine and trichloramine to form. Dichloramine forms
when the chlorine to ammonia ratio is between 5-7:1 and the pH is below
neutral to approximately 4 and Trichloramine forms when the ratio if greater
than 8:1 and the pH is below 4.
How are chloramines added to our water supply
Normally in the first instance chlorine would be added
at source. Chlorine is the preferred additive of many water boards. It has
a much greater ability to nullify bacteria and viruses than chloramine does;
however it does have a relatively short lifespan as a disinfective agent and
there are growing concerns that it forms trihalomethanes (THMs) which are
carcinogenic substances that have been linked to heart, lung, liver, kidney,
central nervous system damage and miscarriages. By adding chlorine at
source, it can rapidly carry out its disinfective role. The next step is to
add the ammonia; this tends to be added further down stream. By adding the
ammonia, monochloramine is formed and the risk of THMs forming is reduced;
in addition the temporal disinfective period is greatly increased giving
longer protection from deleterious organisms – albeit with less disinfective
penetrative power. It has been noted that the half life for chloramines
varies from 1 to 23 days depending on conditions.
Chloramine and its effect on fish
Chlorine and chloramine both cause death in fish by
anoxia i.e. the fish are literally starved of oxygen; however, the
mechanisms involved differ. Chlorine is a major irritant and causes rapid
degradation of the gills by oxidation i.e. gill tissue is destroyed; whereas,
chloramine crosses the gills and directly enters the blood stream of the
fish where methaemoglobin is preferentially formed over oxyhaemoglobin i.e.
the chloramine chemically binds with the iron in blood haemoglobin which has
a deleterious affect on the ability of haemoglobin to bind with oxygen –
thus starving the fish of its oxygen supply. The amount of chloramine that
passes past gills and into the blood is critical in the ultimate effect of
the formation of methaemoglobin and the survival chances of the fish.
Research in Canada has demonstrated that the ‘Estimated
No-Effects Value’ (ENEV) for chloramine is 0.0056 mg/L for freshwater
organisms and 0.0028 mg/L for marine and estuarine organisms. One exception
to these doses is that clam larvae and copepods are extremely chloramine
sensitive and have demonstrated 50% mortality (LD50) at 0.005 mg/L
chloramine concentrations when exposed to chloramine for between 48-96 hours.
Testing for Chlorine, Chloramine, total Chlorine
Palintest Ltd. make a wide range of professional
electronic water testing equipment. A good quality water testing meter that
test for over 37 different types of tests costs between £500 and £700.
Tanita make an economical total chlorine tester (chlorine and chloramine)
which retails at approximately £30.00 sterling and is quick and simple to
use. Yamitzu make a multi chemical test kit for approximately £20.00 and
there chloramine test measure chloramine from 0-1mg/l. There are many more
types of chlorine/chloramine testers on the market including simple to use
dip and test strips but please remember that most equipment available to the
hobbyist will have a resolution of 0.01 mg/l or worse; therefore you really
must take care when interpreting the results and you should certainly take
steps to neutralise the chlorine/chloramine content if you get any reading
Removal of chloramine
There are numerous methods of removing / neutralising
chloramine from our water. I have considered the 3 most popular forms.
Run your water through a duo or tri pod set-up.
The first pod would contain
activated carbon. The carbon catalytically breaks down the chloramine to
ammonia, nitrogen gas and chloride. The carbon deals with the chloride and
a degree of the ammonia. The second pod would contain zeolite in order to
deal with the balance of the ammonia. The contact rate should be between
5-10 minutes. There is a lot of hype and nonsense as to the type of carbon
used; however, as long as the carbon is resistant to channelling and is
changed according to the manufacturers’ directions – it WILL do the job that
Tripod (adapted CBR/Metal Ex
This setup is as above but
with the addition of a 1 micron pre-filter to maximise the effectiveness of
the carbon. If you already own a CBR or Metal Ex system – you could simply
add an additional zeolite pod onto the existing pre and carbon filters –
cost effective and it works.
Again there is a lot of hype
and nonsense on the ability of reverse osmosis units to remove chloramines.
It should be remembered that the flow rate through an RO unit is suited to
chloride removal and partial ammonia removal at the carbon pod at up to 3 mg
/ L. The ro-membrane will then deal with the majority of the rest of the
ammonia released from the catalytic reaction. If you are worried about any
residual traces of ammonia this can be adequately dealt with by the addition
of a deioniser pod and or a post carbon pod (in other words you are building
a 5 stage reverse osmosis unit that adequately removes chloramines) and hey
presto – chlorine and ammonia free water. There are 2 provisos to this
process though. The carbon and resin must be changed at regular intervals
as recommend by the manufacturers’ instructions – this is especially
important if the entering water has a very high (9) initial pH (this causes
the membrane pores to swell and the rejection rate to decrease).
Ideal non chemical removal of Chloramines could be
accomplished with 2 carbon premembrane pods and the newer TFC or "extruded"
RO membranes. The "extra" Carbon pod assures the necessary contact time to
remove Chloramines prior to contact with the RO membrane which will remove
the chlorides and ammonias catalized from the Chloramines by the carbon.
Proprietary Chemical Reducing Agents
Sodium Thiosulphate -
inorganic sodium thiosulphate is incredibly inexpensive and fast working.
It is added to the chloramine containing water. The thiosulphate destroys
the chloramine molecule and also effectively neutralise chlorine,
unfortunately the resulting ammonia still needs to be dealt with if your
tank is running at a very high pH. In a discus tank of pH of 6 this ammonia
would be converted to the much less toxic ammonium and would over time be
consumed by the filter bacteria etc.
+ NH2Cl + H2O ® SO4 + H+ + HCl +
Hydroxymethanesulphonate – this is an alternative
product and one that is more favourable than the sodium thiosulphate. It
readily breaks down the chloramine, neutralises chlorine and binds up the
ammonia. It is found in Amquel, and I suspect Ammo-Lock 2 – a product I
have personally used with success.
I would add one point of caution to the above products
in that whilst they do the job they claim to do there is still some concern
on the resulting by products and their effect on developing eggs, fry,
larvae etc; therefore if you are a breeder, you may want to consider
alternative methods to the use of chemicals.
Department of the Environment, Department of health, (2000), ‘Canada
Gazette’, CEPA Environmental Registry, Vol 134: No. 28
A., Nichols; R., (1985), ‘Composition and method for removing chloramine
from water containing same’, US Patent 4,554,261
D., Eaton, J, (1975), ‘Chlorine-induced mortality in fish’, Transactions
of the American Fisheries Society, 104, pp 800-802
(2001), ‘Chemicals in drinking water: chloramines’, Scottish Centre
for Infection and Environmental health, Glasgow.
Home-Farley, R., (2003), ‘Chlorine and the Reef Aquarium’,
(2003), ‘Lenntech Disinfectants Chloramines’, http://www.lenntech.com/water-disinfection/disinfectants-chloramines.htm
GE infrastructure Water & Process Technologies
(1997 ) "Chloramines", http://www.gewater.com/library/tp/813_Chloramines_.jsp
Francisco Public Utilities Commision, (2003), ‘In Depth Chloramination Q&A:
Impact on Animals and Environment’, Sans Francisco Public Utilities