Re: What are the Effects of Swimmers on Pool Chemistry

Hi Mike,

Well, the effect swimmers have on pool chemistry really depends on how 
many swimmers use the pool relative to the frequency of the pool water 
being recycled and filtered.  Public pools must constantly circulate fresh 
water into pools containing various chemicals.  Circulating fresh, treated 
water will have a strong dampening effect that swimmers have upon the 
chemical balance of the pool water.  Any effects that swimmers cause on 
the pool chemistry is likely to be only short-lived and not too profound.
 
The addition of swimmers to a pool will have the following effects on the 
pool water:

1. Depending on the initial water temperature, swimmers could increase the 
temperature - especially large numbers of swimmers.  This can increase the 
rate of evaporation and alter the concentrations present in the pool's 
chemistry.

2. Salinity of the water could also increase due to swimmers sweat, 
although this is probably a relatively very small contribution.

3. An increase in organic material content - such as saliva, mucus and 
(possibly, yes) uric acids.  Once again, these will not be a large 
contribution to the pool chemistry. 

4. Agitation of the water, swimmers will mix the pool water quite 
effectively making the pool chemistry quite homogenous.  This will also 
increase the rate of evaporation occurring.

Typically, disinfectant materials, such as salts of chlorine oxoacids like 
sodium chlorate (I), an acid with fairly strong oxidizing properties are 
added.  Aqueous solutions of chlorate (I) undergo decomposition and 
disproportionation slowly:


decomposition:

2ClO-(aq) - 2Cl-(aq) + O2(g)

disproportionation:

3ClO-(aq) - ClO3-(aq) + 2Cl-(aq)


The disproportionation reaction of chlorate (I) to chlorate (V) is 
favoured by increased temperatures.

I hope that this goes at least some way to providing you with an 
explanation.  You may find further information relevent to this topic from 
local goverment public health regulators.

Chris Wilson, R&D Chemist, Cooper Vision,
Southampton, England.