Swimming Pool Blog
by Mike Selsor, January 12, 2011
Pool Salt systems, what they are and how they work
“Hi, I’m changing from a chlorine, to a salt water pool, what do I need to do” This is a question I get a lot these days from folks trying to figure out exactly what they need for this technology to work. A common misconception is that when switching to a salt generator, your pool will become a “salt water pool” or in other words would be like the ocean and kill bacteria based on the salinity instead of a sanitizer like chlorine.
This simply isn’t the case, in simple terms yes the pool will have a concentration of salt water just like the ocean, but it couldn’t be any more different from our blue seas. The concentration of salt in the ocean can be as high as 35,000-40,000 Parts Per Million or PPM. In comparison our body is about 4,000 PPM and fresh water is considered anything below 1000 PPM salinity concentrations. The salt water pool’s “sweet spot” for salinity is between 2700 and 3400 PPM. This level is usually below what most swimmers can even taste. So if the salinity in the pool doesn’t do the sanitizing, exactly what does?
The simple answer would be chlorine! Yes that’s right, salt water pools still use chlorine to kill bacteria in the water. The difference is now your pool makes chlorine from breaking the salt in to its two main parts; Sodium and chloride. How does it do this, you ask? This is where the salt generator system comes into play. Each salt pool system consists of 2 separate pieces of equipment, the salt generator cell and the salt control system and power supply. Inside the salt cell are many plates all stacked and charged opposite of the neigboring stack, so one salt cell plate would have a negative the next cell is a positive charge and so on. The number of plates in a salt cell is determined by the size of pool or how many gallons of water the unit can chlorinate effectively.
As the salty water passes through the cell a process known as electrolysis breaks the salt down into chlorine on one side of the plates and caustic soda and hydrogen at the other. The chlorine effectively super chlorinates or shocks the water as it is created and kills off any bacteria, while a residual amount is retained to continue to sanitize. After the sanitized water passes though the salt cell , we realize the real beauty of the salt pool system. The chemical components come back together to once again form salt and the process starts all over again. So what that means is - once pool’s salt level is brought up to a proper PPM, no additional salt will need to be added, only what is either evaporated or splashed out of the pool.
This brings me to the next question I typically get, which is “how do I determine how much salt to put in and what kind?” well the first part of the question isn’t too easy as each pool will have a different amount of salt already in it. A 30,000 gallon pool would take about 800 pounds of salt be added into the water to bring it to 3200PPM. There are several different ways to see how much salt is actually in the water. The most simple and least accurate is to use a salt test strip test to determine salinity. The best option would be an electronic device that is dipped into the water to determine how much salt content is present - these work by simply measuring resistance of the water or how well it passes electricity.
The second part of the question, what kind of salt, is much easier to answer. You want to get as pure salt as can be found, as impurities will cause scale buildup on the cell. At least 99% pure salt is recommended by most salt generator system manufacturers, and there are now companies that are producing salt specifically branded as “pool salt” which is very pure. The pools chlorine is checked just like any other pool, with the appropriate test kit. Basically the only difference between a normal pool and a salt water pool is how the chlorine is introduced; all other aspects of maintenance are the same. Although a closer eye should be kept on water balance as an imbalance can cause scaling or corrosion or a host of other problems.
The chlorine generator salt cell may be the business end of the system, but the heart and soul would be the salt controller and power supply. This piece of electronics is the most expensive component in the system and it is also the most technically advanced. Most systems on the market now will tell you when you have a low/high salt condition, and will have a few different settings for chlorine output. The more advanced systems can be as sophisticated as to tell you the exact salt PPM and even how much chlorine is in the pool. They can also let the user know of any problems with the cell and clean the cell automatically when needed or alert the user to the need to clean scale from the salt cell.
Most salt water systems can be hooked up to a total pool controller system which monitors every aspect of the pools chemistry and can control all systems for a completely hands off approach to pool maintenance. Most control units also have a super chlorinate or “shock” function when needed to get rid of any chloramines that may be present or after a high bather load is experienced. During warm summer months the system may need a longer run time to fully sanitize the pool water and to prevent algae growth. The control system also converts the 110 volt household current to 12 volt or 24 dc power for the cells electrolysis plates.
All in all there are a lot of benefits to going to a salt system, the major one being that chlorine tablets will never need to be purchased again as the pool makes its own. Most swimmers in a salt pool report that the water feels softer and their skin felt smoother and softer after a swim as well. Also a homeowner will not have to touch chlorine which can be dangerous to your health and skin. There are however other maintenance that needs to be performed, such as making sure a stabilizer is used and enough present ( CYA levels between 60-80PPM like any other pool) so the chlorine doesn’t simply bleach out in the sun. Also a close eye on water balance, especially PH and Calcium Hardness levels, should be kept to avoid any scaling or corrosive conditions.
Another benefit is that most swimmers won’t feel the effects of the chlorine as much because most chloramines, the used up chlorine that typically causes most eye/skin irritation, is burned up when electrolysis happens. A salt water pool has many benefits that most homeowners will enjoy, so what are you waiting for? Stop buying chlorine! Buy a salt water chlorinator instead!
If you have a salt pool system already - tell us by commenting below how you like using a saltwater generator for your pool!