One of the biggest questions we get asked on each project is about the chemical treatment options. Most people want to select the “best” products available. The truth is, depending on the specifics of your project, what is considered “best” varies. For the most part, all commercial aquatic facilities are required to have a halogen in the water for instant sanitation. The most common types are Sodium Hypochlorite (liquid chlorine), Calcium Hypochlorite (tablet chlorine), Bromine (non-chlorine sanitizer), or Saline (on-site chlorine generator). Here are some things to consider about your chemical selection:
- Sodium Hypochlorite (liquid chlorine) is approximately 12% free available chlorine. Sodium hypochlorite must be stored in a covered tank and a room that is ventilated to the exterior. Liquid bleach is a mild hazard. It is relatively reactive with acidic chemicals and organics.
- Liquid chlorine has some advantages, the most important being safer handling. In a 12 percent solution, liquid chlorine is stronger than the 5 percent solution typical in household bleach and, as a liquid, it’s also relatively easy to monitor and introduce into pool water. Liquid chlorine is injected into the main pool plumbing and is disseminated into the pool. It’s easy to gauge and control. Liquid chlorine costs approximately $1.35 per gallon. Its pH is 13.0.
- Liquid chlorine also has its disadvantages. Because of its short shelf life, liquid chlorine quickly loses its potency and effectiveness. At the manufacturing facility, the liquid is mixed to a 14 to 16 percent solution, but typically deteriorates to about a 12 percent solution by the time it reaches the supplier and to a 10 percent solution at poolside. Sodium hypochlorite is susceptible to the heat and sun and can drop to as low as a 5 percent solution in one month. Shelf-life is typically between 30 and 50 days. When the tanks are refilled, most are not cleaned out, and the new chlorine is diluted when added to the old chlorine. As a result, potentially twice as much chlorine will be required to achieve the desired effect. Therefore, storing liquid chlorine can quickly become a poor investment.
- Calcium hypochlorite tablets are placed in canisters and pool water is bypassed through the erosion feeders, dissolving the tablets and introducing chlorinated water back into the pool. Clogging with the feeders was an issue in the past, but most of those issues have now been resolved through design.
- Calcium hypochlorite is easier to handle than liquid chlorine. It has a pH of 12, so it doesn’t require as much buffering agent as liquid chlorine. It’s more expensive than liquid chlorine (approximately $1.80 per lb.), but it has a much higher concentration of available chlorine (65%). First-dollar costs are similar, and even thought the tablets are more expensive than liquid, the need for fewer buffering agents and a longer shelf life provide trade-offs that make the operational costs manageable. There is no need for the barrier systems and huge storage tanks required for liquid chlorine.
- Calcium hypochlorite is a Class 3 oxidizer and is corrosive. It has a 4-hour rating with H-2 occupancy or 3-hour fire rating with an H-3 occupancy. It is flammable and high in hazard. Some codes limit storage from 10 to 200 lbs. in a single location. Typically, this amount can be increased if the room has a 2 to 4 hour fire rating, the space is provided with an appropriate sprinkler system and it is properly ventilated. Additional storage of calcium hypochlorite can be provided in an additional “haz-mat” room if the building has such a room.
- Bromine gained interest in the early ‘90s as a replacement for chlorine. Twice the bromine is required to reach the same oxidation potential of chlorine. Bromine is a much less aggressive oxidizer compared to chlorine. It doesn’t combine with organics, therefore chloramines are not produced which cause the smell in a natatorium. There are claims that bromine is less irritating to swimmers.
- Problems exist with bromine because it is less active, it cannot react as quickly, compared to chlorine, when there is heavy organic loading and a large number of bathers enter the pool at one time. The result is cloudy water.
- Bromine by itself is costly. First-dollar costs are acceptable, since the distribution system is similar to that used by tablet chlorine. Second-dollar operation costs, though, are significantly higher. Compared to tablet chlorine, bromine can cost a little less than twice that of tablet chlorine. In addition, since it isn’t as active as chlorine, systems need twice as much to achieve the same sanitation level, making the operating costs of a straight bromine system prohibitive for many applications.
- Salt systems generate pure sodium hypochlorite at a near neutral pH and therefore have less effect on pH than most other pool chlorines. The pH must be controlled like usual, and is influenced mostly by the total alkalinity of the water.
- Hypochlorous acid is produced when an electrical DC current is passed between the positively-charged anode plates and the negatively-charged cathode plates in the chlorinator cell. This solution flows, after mixing into the water leaving the filter, directly into the swimming pool.
- This continuous introduction of hypochlorous acid ensures the continuous sanitization of the pool water and will provide the necessary chlorine residual required when the equipment is operated properly. When the hypochlorous acid produced in the chlorinator has destroyed the bacteria in the pool, it reverts to salt (sodium chloride). This means that salt is continuously recycled during this process.
- Since the chlorine is ultimately converted back into salt, it gets recycled and extra salt will only need to be added infrequently (only a small amount will need to be added once or twice a year to replace the salt lost due to splash-out or backwashing).
- Manufacturers report the following advantages of salt systems (most of which are highly debatable):
- Saves money
- Fixed costs versus variable chemical costs
- Improves the quality of the water and enhances bather comfort
- Stabilizes pH and easier water balance
- Enhances indoor air quality
- Reduced pool maintenance and ease of operation
- Lease payments are tax deductible as an operating expense
- Saline systems are often desirable on LEED projects (where feasible). Using table salt with the saline system to create chlorine means that there is no longer a need to store commercial chlorine at a facility as chlorine will be manufactured in-line as needed. Instead, bags of salt will be stored. Also, by converting to CO2, facilities can eliminate the need to store and use muriatic acid and eliminating the potential for spills. By removing most of the hazardous product from the pump room, facilities eliminate the potential for any accidental spills or cross contaminations of chemicals causing fires and or toxic off-gassing, making the facility more environmentally-friendly.Each of these options have been used successfully in commercial applications. It’s best to consider each of these when starting your project, then evaluate the pros and cons based on your specific needs.