Where & When to Use Cyanuric Acid

Cyanuric Acid is also known as chlorine stabilizer, or just stabilizer, because its job is to help stabilize chlorine levels in outdoor pools. The UV portion of sunlight outdoors causes chlorine levels to drop rapidly even if there is no bather load. To help slow the dissipation of free chlorine by sunlight the ideal level of stabilizer, Cyanuric Acid, would be 50PPM. This level has been established because at lower levels it is not effective, and at higher levels it prevents chlorine from working, killing germs effectively. The process translates directly into cost savings by slowing the use of Chlorine in outdoor pools. Stabilizer is not used in Indoor Pools because the lack of UV from artificial light means that chlorine in indoor pools does not dissipate as fast. Chlorine that come as chlorine and stabilizer premixed should be avoided for 2 reasons. The first is cost, they charge too much for the convenience, and secondly, when you have reached 50PPM you still need to feed chlorine, but cannot feed more stabilizer. Stabilizer does not get used up, but the levels slowly go down due to dilution, just like alkalinity, or calcium hardness. Note that the only way to lower stabilizer levels is by dilution. It cannot be destroyed. Once the initial dose has been dissolved in the pool normally an addition once a week is all that is required to maintain 50PPM. For the initial dosage calculate the amount needed to achieve the 50PPM given your pool capacity, put it in the surge tank, skimmer, or on the main drain, anywhere with good flow and be aware that it dissolves very slowly. Tests will show that as it dissolves over the next 2 or 3 days the levels will slowly go up to the calculated 50 PPM. Don't add more for 3 days. Also remember that physical chemistry is very accurate. At the end of a week you may need to top up 5 or 10 PPM, do the calculation again, and again apply and wait for it to dissolve over several days. The formula for stabilizer is 8 pounds of stabilizer in 100,000 US gallons gives 10PPM.

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.

Flocculation/Alum/Aluminum Sulfate

Alum is a generic industrial chemical widely used as a flocculant, to help small suspended particles settle or get caught in a filter as they become larger by clumping together. The chemical is AL2(SO4)3. Alum is dissolved in water to form aluminum hydroxide with precipitates into white flocs which accumulate as a gelatinus mat on a filter bed, improving filtration by helping to catch small or fine particles which would otherwise pass thru. Alum works best when the Ph is between 7.4 and 7.6. The doseage is normally 4 to 5 ounces per square foot of sand filter area, and is normally premixed with water and poured into a skimmer. Backwashing removes the Floc layer, so it should be applied after a backwash, and renewed after each subsequent backwash.