What is liquid chlorine…really?
One of the most popularly chosen forms for sanitizing pool water is liquid chlorine. It is widely used in swimming pools both commercial and residential. Technically speaking liquid chlorine is a chlorinating compound made of these three ingredients, liquid chlorine, water, and sodium hydroxide. The correct term is liquid sodium hypochlorite. It is more correctly referred to as liquid bleach. The popularity of liquid sodium hypochlorite is primarily due to its availability, cost, and efficacy. Also, sodium hypochlorite will not contribute to an increase in calcium or cyanuric acid. It remains one of the purest and simplest formulas for the disinfection of bacteria and the prevention and removal of algae in swimming pools.
Brief history of liquid sodium hypochlorite its other uses etc.
Early uses of sodium hypochlorite included: Disinfection of medical facilities and hospitals, preventing the spread of disease from corpses, slaughterhouses, and food production. In the early 1900’s liquid sodium hypochlorite was used to disinfect drinking water. The use of chlorine disinfection at water treatment plants was highly effective in exponentially reducing fatalities from waterborne diseases such as cholera and typhoid fever.
History of Use: Public Pools to Backyard Pools
Since liquid sodium hypochlorite was effective in the disinfection of drinking water, it was only natural that it would make its way to swimming pools. Liquid sodium hypochlorite is preferred at public pools because it is safer to store then either chlorine gas, tri-chlor or calcium hypochlorite. As backyard residential pools began to gain popularity in the 1950’s and 60’s liquid sodium hypochlorite played a key role in disinfection and water clarity. Before chlorine tablets, feeders and floaters began to make their way into pools there was a simple routine. Sanitize with liquid sodium hypochlorite and manage pH with muriatic acid.
How tablet convenience replaced liquid practicality in the market
While liquid sodium hypochlorite was a popular choice for backyard pools there was a problem. Sodium hypochlorite is un-stabilized. This means that the summer sunlight destroys the free chlorine within a few hours. Since this problem began to be recognized the practice of adding extra amounts of liquid sodium hypochlorite in the late afternoon or evening was incorporated.
In 1956 Monsanto began to produce and distribute cyanuric acid (CYA). At levels of 30 ppm CYA helps free chlorine residuals last up to eight times longer. There is an incredible benefit from adding CYA to the pool water. In the late 1960’s and early 1970’s solid tablets of stabilized chlorine known as isocyanurates made their way into residential swimming pools. The selling point was convenience for the owner. The tablets could be added to an inline feeder, or a floating container known as a floater. The advantage was that the stabilizer to protect free chlorine from the destruction of sunlight was built right into the tablet. Voilà, instant convenience for the modern pool owner. As this system of treating backyard pools grew in popularity liquid sodium hypochlorite was pushed out as the main source of pool sanitization. Liquid sodium hypochlorite became more of a back- up or shock to Tri-Chlor tablets in pools.
How the perceived convenience of dry chlorine causes complications.
While the two-in one convenience of Tri-Chlor tabs grew there was something happening beneath the surface that pool pros soon noticed. Early on there was a perception that higher levels of CYA could lock up the effectiveness of the chlorine. This was known as “chlorine lock” and whether it is mythical or factual it was the source of many a bar room brawl. From academia to the field tech the debate over CYA has been a mainstay in the swimming pool industry for over 30 years.
One thing that is certain to most pool service techs is that pools on Tri-Chlor tabs with increasing amounts of CYA can be a struggle to maintain. There is more of a challenge to keep free available chlorine levels good, and many pools develop algae toward the end of the season. Users of tri-chlor tabs have become aware of some side effects that lead to complications in water treatment.
One crucial factor is understanding the amount of CYA being released from the continual use of Tri-Chlor tablets. Most of an 8 oz. Tri-Chlor tablet consist of CYA. Over 54% of one tablet by weight is CYA with the other 46% being chlorine. At one time the concept of more is better ruled. Now the latest information shows too much CYA leads to the increased need to drain and dilute. Not a popular choice during a drought or water restrictions. One point that has become noticeably clear lately is that using Tri-Chlor tabs has made maintenance of pool water more complicated.
Other points regarding this are the fact that Tri-chlor tabs are very acidic which leads to more soda ash to balance pool water. Also, CYA interferes with the total alkalinity reading if the levels are higher than 60 ppm. Meaning that total alkalinity readings can be falsely measuring too high. This leads to more complications and adjustments. Now there is emerging research from the Centers for Disease Control (CDC) that shows it takes a lot more chlorine and contact time to inactivate bacteria.
Further research shows there must be a proper ratio between the ppm of free chlorine and CYA present in the pool to effectively kill bacteria and prevent algae. Current theories suggest using a ratio of 7.5% ppm of free chlorine times the CYA ppm level. For example, if CYA level is 60 ppm it would take 4.5 ppm of residual chlorine to kill bacteria and prevent algae growth. 60 x 7.5%=4.5 ppm. The CDC and Model Aquatic Health Code (MAHC) suggest a CYA to chlorine ratio of 20:1 in order to effectively inactivate bacteria. That means at 20 ppm CYA there must be 1 ppm of FC in order to effectively inactivate bacteria such as E. coli or Giardia. While the debate continues it is clear to see that the perceived convenience of Tri-Chlor tablets leads to a lot of complications and additional work for service pros.
What about salt generator pools?
Moving into the 90’s devices began to become more popular. One that increased in a big way was the saltwater generator. These units were sold to many new pool owners under the auspice of being a “non-chemical” pool that relied only on salt to purify the water. Many new pool owners were not aware that the salt unit installed on their new pool was a small home version of a liquid chlorine factory. The saltwater generators in swimming pools do the same thing as a liquid chlorine plant only on a smaller scale. They are more correctly referred to as chlorine generators.
Like any type of chlorine sanitized swimming pool, a chlorine generator pool still needs to have a level of CYA to prevent rapid burn out of chlorine from the UV rays of the sun. CYA levels in a salt pool are good at 30 -50ppm. Using the 7.5% ratio with a CYA of 30 the ppm of FC needed from the chlorine generator would be 2.25 ppm. At times, a chlorine generator may need a back up of manually added chlorine to keep the water quality good. This could be a result of heavy swimmer load, equipment failure or power outage. Liquid sodium hypochlorite is one of the best back up sanitizers for chlorine generator systems. This is due to the by-product that comes from the use of sodium hypochlorite. Let’s look at the different types of chlorine and their by-products:
- Calcium hypochlorite –calcium
- Tri-Chlor –cyanuric acid CYA
- Liquid Sodium Hypochlorite –sodium chloride
The only by product left from liquid sodium hypochlorite is sodium chloride better known as salt. Out of all the types of chlorine liquid sodium hypochlorite gives a chlorine generator pool what it needs to function properly. This helps replace salt lost from backwashing or splash out.
Liquid sodium hypochlorite is also the best sanitizer for secondary systems like ozone, UV and AOP. Since liquid does not increase CYA levels or calcium hardness, the cells and units will stay cleaner and scale free longer.
The benefits of a simple liquid chlorine system for service techs.
Despite all the information, questions and confusion regarding CYA and the use of Tri-Clor in swimming pools, there is still a dependable, safe, and simple way to get chlorine sanitizer. Liquid sodium hypochlorite has been proven through the history of pools to be one of the most cost effective, easy, and safest ways to disinfect pool water.
Benefits of Liquid Sodium Hypochlorite
- Affordable
- Easy to use.
- Safe for storage as it is non-flammable and non-combustible.
- Creates an instant measurable residual of free chlorine.
- Does NOT contain calcium or cyanuric acid.
- Beneficial as a back up to chlorine generator systems
- Ideal for use with secondary sanitizing systems like ozone, UV and AOP
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