Swimming pools basically are large collections of water, and like any body of water, they are susceptible to various issues. Among the most noticeable problem is when the water gives off strange or bad odors. The most common cause of funny smells in a swimming pool is chloramines, which result when pool chlorine combines with ammonia or nitrogen compounds, like urine or sweat.
Chloramines in the water contribute to the pool's combined chlorine reading since most chlorine testing kits are unable to distinguish between free chlorine in the water and the chlorine that has bonded with other compounds to form chloramines. The chlorine that is bonded into chloramines, though, is a poor disinfectant and has the added drawback of causing foul smells as well as eye and skin irritation. The chlorine smell we associate with swimming pools isn't normally caused by the free chlorine sanitizing the water, but by the chloramines that have formed when some of the free chlorine bonds with other compounds.
In terms of the technical chemistry, chloramines form by replacing the hydrogen or ammonia atoms with chlorine atoms in certain compounds, such as urine and sweat. Chlorine also combines with nitrogen in rain or with the ammonia in swimmer saliva. As the free chlorine is captured in other compounds, it is no longer available to serve its principal function as a disinfectant. Hence, a pool high in chloramines is a pool with less sanitary water.
If your pool smells funny and looks cloudy, chances are it has chloramines. Another symptom is that the pool's combined chlorine reading will be above 0.2 parts per million (ppm). The combined chlorine level (the chlorine that is "combined" with other compounds) is calculated by subtracting the free chlorine level from the total chlorine level.
High levels of chloramines can also be indicated by symptoms in people. Chloramine-heavy swimming pools frequently cause swimmers to complain of irritated skin or eyes. There is also evidence that chloramine can contribute to respiratory problems in swimmers who spend a lot of time in the water.
The best method for eliminating chloramines from a swimming pool is to shock, or super-chlorinate, it. Pool professionals call what happens in a pool during super-chlorination "breakpoint chlorination," and it's necessary in order to eliminate chloramines. Basically, a swimming pool in which chloramines are present will need to be super-chlorinated to 10 ppm or more and held there for at least four hours. During super-chlorination, actual chlorine is "burning up" or oxidizing the chloramines and removing them from the swimming pool.
The best way to prevent chloramines is to maintain recommended chlorine levels and also to shock your pool regularly. The recommended range of chlorine in a pool is 1 to 2 ppm.
The Importance of pH
Remember, though, that chlorine shock will raise pH because chlorine is alkaline. After a pool shock treatment has been completed, always measure pool pH and adjust if necessary. The most important reading in a swimming pool's water is its pH, and it must be maintained at recommended levels. A swimming pool's pH should be held at 7.4, if possible.
When a pool's pH is too low or too high, chlorine levels are always negatively affected. And that can cause many problems, including issues with chloramines. Raise a pool's pH by adding 1 pound of sodium carbonate per 25,000 gallons of water. Pool pH is lowered by using muriatic acid, strictly following package instructions.