Water Quality in Swimming Pools

From DrydenAqua

Relationship between Mono Di and trichloramine

The relationship between mono, di and trichloramine is a function of the pH of the water and the concentration of ammonium and chlorine in solution.

From German DIN standards 19643 Conditioning Swimming Pool Water chloramine production is a function primarily of the pH of the water. The graph opposite  shows the relationship between chloramine formation and pH.

By way of example,  if we take a pH of 7.4, then there will just be free chlorine and  mono chloramine in the water, technically there should be zero or very little dichloramine and trichloramine. However it is trichloramine that has the characteristic smell, and it is predominantly trichloramine that  stings your eyes in swimming pools. This means that there must be a low pH environment at some point in the system in contact with the water. The production of trichloramine is not a reversible reaction, so if there is a low pH at some location,  then trichloramine level will continue to increase

The low pH is caused by the biofilm  which can develop on every surface in contact with the water. By changing the sand to AFM®you reduce the bacterial load by around one million times.  However there will still be bacteria growing on the pipe work and on the tiles. NoPhos will remove or reduce the growth of these bacteria and should be dosed continually into the water.  The NoPhos dose rate should be adjusted to give a zero phosphate reading.  However even if you record a zero phosphate reading you must continue with the NoPhos because phosphate will continue to increase due to the bathers, influent water supply and from other chemical products used in pools.

If the above is accomplished and you still have trichloramine present, it will be a function of the operating procedure, the equipment used or there is a dead area in part of the water treatment circuit. Analysis of the water needs to be conducted at different points in the system to determine the source of the contamination


Chloramines are formed in water by reaction between chlorine and dissolved proteins and chemicals such as urea (NH2)2CO. The following chlorine reactions are taken from German DIN standards 19643

NH4+ + H2O  ======>   H3O+ + NH3 (bacterial mineralisation decomposition of urea from urine, sweat, etc.)

NH3+Cl2 <<======>>     NH2Cl     monochloramine………………………. pH 6 to pH 8

NH2Cl + Cl2 ======>>    NHCl2 dichloramine ………………………… pH5 to pH6

NHCl2 + Cl2 ======>>  NCl3 trichloramine …………………………..pH <5

NH2R + Cl2 ======>>          NHRCl    alkylmonochloramine  = organo chloramines

(  <<======>> denotes a reversible (equilibrium) reaction; =====> denotes a forward one-way reaction.)



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