Managing Combined Chlorine
There is no one treatment that will take care of this problem, but by combining several treatments the problem can be managed.
The first recommendation is to enforce the rules requiring patrons to shower before entering the pool. Studies show that this can result in a reduction of 25% in the dirt load that otherwise would have to be dealt with by the filters and treatment chemicals. This is like reducing the bather load by 25%, or increasing the dirt load that needs to be treated by filtration and chemical treatment. It's worth doing.
Air quality is important for patrons and staff alike. Typically it gets worse in the winter. Poor weather increases bather loads, people spend more time indoors. Modern air handling systems are typically energy efficient. This means that the colder it is outside the less fresh air is allowed into the building. This is opposite to what is needed. Find out how to manually override this energy saving feature so when it is busy in the winter and more make up air is needed it can be provided. The heating bill will be higher but this is how you get the same clean air that is enjoyed in the summer.
If sand filters are being used consider adding a flocculent such as Alum (aluminum sulfate) an inexpensive standard industrial chemical that has been used for this purpose for years. This will form a gelatinous mat on the filter bed to help catch particles which would otherwise pass thru the filter. The formula is 4 to 5 ounces of Alum per square foot of filter area after each backwash. Products like c-clear work equally well, and like many other commercial flocculants they are pre-dissolved preparations of Alum. DE is a much finer media and no flocculent is needed. Anything that can be filtered out lowers the dirt load that otherwise must be treated chemically.
Dose the pool regularly with an Oxidizer such as Potassium monopersulfate (Oxyout, Oxybrite, Oxone, Impact). Weekly oxidation reduces bather contaminants and therefore chloramines, giving the improvements in air and water quality desired. The use of FAS-DPD test kits for chlorine measurement is recommended when using a monopersulfate based oxidizer. A recommended dosage would be 1 lb/10,000 gallons. Studies have shown that weekly oxidation with monopersulfate is about 10 times more effective than super chlorination .
** Please note that all the above "Oxy" products will affect the standard DPD combined test through the introduction of iodine in the water. It will be necessary to change to a Taylor test kit K-1518 or adding R-867 to an existing K-1515 test kit to allow proper combined calculations. **
Super chlorination or Breakpoint Chlorination. Not recommended. For this process to be successful time and careful control of chlorine levels are required otherwise unintended and undesirable consequences occur. Time, generally speaking it is not available, which means successful breakpoint chlorination does not happen. Overdosing with too much chlorine aggravates the problem, volatile chlorinated disinfection by-products are formed which further aggravate the situation. These can be nitrogen trichloride, dichloromethylamine, dichloroacetonitrile, cyanogen chloride, to name a few.
It is best to use chlorine for the job it is best at, namely disinfection, and to use an oxidizer for the same reason.
Supplemental UV treatment works, and provides further improvements in water quality. UV at germicidal doses provides supplemental disinfection, and a constant slow reduction in chloramine levels. (Just like O3). UV chambers normally process the full flow of the filtration system providing deactivation of pathogens which are slow kills with chlorine, and expose all the chloramines to UV treatment with each pass, not partial treatment as used in bypass or slipstream systems. Oxidation is still required and use of an oxidizer as described above is still recommended with UV for optimal water quality.
The effects of ozone are a slow constant oxidation and reduction of chloramines, with some supplemental disinfection, but the process has recently lost favour due to high equipment and maintenance costs.
Water replacement based on bather load to reduce the concentrations of combined chlorine and precursor compounds is also recommended. A formula of 40 litres of fresh water per bather per day would be ideal. (This is already required by law in Ontario ) A reduced version of this formula can be tried; a program starting at 5 or 10 litres per bather per day would be a start. Keep records and change one thing at a time so you know what your results really are. Results of all these practices are cumulative, if they are all used the lower doses of fresh water will give good results, if a step or two is missed higher dosages will be required to achieve good water and air quality. Bather load is the biggest factor, higher load requires more treatment or fresh water, adjust accordingly.