Authored by: Steve Goodale (Swimming Pool Steve)
With so much positive buzz about swimming pool and hot tub salt water chlorination systems, it can be easy to miss some of the negative aspects of this form of chlorination. Before you make the decision to convert your pool to salt water, you need to understand a little bit about the risks associated with this alternative form of sanitizer delivery.
The top 3 things that you should know about salt water systems before deciding whether you want one for your pool or hot tub are:
Chemical balancing - Salt water is NOT maintenance free
Draining requirements - Bylaws relating to discharging of salt water pools
Galvanic corrosion - A complicated electrical process that can ruin your pool
The first thing that you will notice is that the chemical balance process that you use for your pool or spa will change when you add a salt water system to the pool. Where most swimming pools will tend to have a low pH due to the low pH of most traditional chlorine products, a salt water pool will tend to have a high pH due to the chlorine produced from the salt system having a very high pH. This alone is not necessarily a problem since chemical balance is a part of regular pool and spa maintenance. The problem is that many pool owners mistakenly buy a salt system thinking that it does not require maintenance, and if corrective action to keep the pH down is not taken, then you have a recipe for disaster on your hands. High levels of pH, especially anything over 8.0 (which is very easy to do with a salt chlorine pool,) can put the pool into a "scaling state" where corrosive scale begins to form on various parts of the pool. Even worse, if you have high calcium levels as well as high pH, then you will have excessive scaling problems in your pool. The scale itself can cause damage to integral pool systems and interior finishes and can contribute to very early failure of the chlorine generation cell which can be costly to replace. If you decide to purchase a salt water system then you must also decide to learn how to understand water chemistry to make sure that you do not experience early failure of your system or damage to you pool and its components.
The next item to consider is how you will drain your pool when the time comes. Usually a swimming pool is pumped out to the curb in front of your house and then the water runs into the nearest sewer grate. Some larger urban centers are now beginning to ban salt water swimming pool draining into the street. Many cities are implementing a bylaw which requires salt water pool owners to pay to have their water trucked away, or choose to send the water into the sanitary drainage system for their house. Both of these options are far from ideal, and many more municipalities are looking towards this kind of legislation. Be sure to know the bylaws in your area about waste water to ensure you are not taking on additional maintenance costs for your pool without realizing it. This becomes even more of a concern if you have a sand filter that requires regular backwashing as the only place to backwash salt pools in discharge restricted areas is into the sanitary drainage system of your house or onto your property somewhere without flooding into your neighbor’s property. A cartridge filter is a good option to be paired with salt water pools in areas where water discharge is restricted.
The final factor to consider when thinking about converting to salt water is something called galvanic corrosion. This is the process where dissimilar metals are submerged in an electrolyte solution developing a current that travels in between metal components in the water. When submerged, these differing metals will develop a tiny potential electrical difference between them which is called "voltage". Submerging dissimilar metals in salt water is how you make a battery, and if action is not taken to prevent this from happening with your pool, then you will have a 25,000 gallon battery that operates 24/7 in your backyard - slowly eating away at your pool. Inside the pool and part of the pool equipment are all sorts of metals such as nickel, galvanized steel, copper and titanium. Since all of these metals are located in the salt water, it is possible to develop a small electric charge across these different metals. Over time this very small voltage would cause severe corrosion of whichever metal is the weaker (less noble) of the two. Titanium and stainless steel are more resistant where copper, galvanized steel and zinc are much more inclined to corrode during this process. What this boils down to in your pool is rotted wall panels on vinyl pools, stainless railing and light niche oxidizing and premature failure of heater internals, to name a few. The good news is that there is a system to help prevent this from happening. The bad news is that very few salt water pool owners know about it or have one installed. A sacrificial zinc anode or series of zinc plates are added to the system so that they become the weak link (least noble) metal in contact with the pool water, and this will help to protect the integral pool components against galvanic corrosion. Zinc will corrode faster and more readily than any other metals. So as long as you keep the pool in fresh supply of zinc plates to corrode, then all the other metal components will avoid the brunt of the damage. Be sure to understand the process of galvanic corrosion before you install a saltwater system to prevent damage to your backyard investment.
Salt chlorine generators do have the benefit of not dealing with liquid chlorine and salt can be easier on the eyes and leave your skin feeling silky soft when you get out of the pool. These benefits however are not worth potentially destroying your pool and equipment so be sure that:
The pool is electrically bonded and all equipment such as the heater and pump have a bonding wire connected to the casing
You install an inline sacrificial anode to mitigate the damage of galvanic corrosion
You understand the relationship between pH and total alkalinity and how to keep these values within the ideal ranges
If you take these steps you can enjoy the benefits of salt water while limiting the potential for damage and expensive repairs in the future.
Swimming Pool Steve is a second generation pool and spa expert located in Ontario, Canada.