Salt Water Pools - How Do They Work?

by Mark Manning
President
Watermaid of Canada Inc.

Relaxing in a lounge chair and soaking up the sun's rays while your pool automatically manufactures chlorine seems too good to be true. But it is possible with a chlorine generator. No more weekly trips to the pool store to buy chlorine and then the hassle of dosing the pool and storing the left over where the kids won't get at it. A chlorine generator will automatically take care of these chores for you! This self-regenerating process works by converting dissolved salt in the pool water into liquid chlorine. As soon as the chlorine has done its job of cleaning and sanitizing, it reverts back to salt to start the whole process over again.

Q. We are planning on buying a chlorine generator for our pool. How do they work?

A. A salt-water solution is passed between a cathode and an anode, which are positive and negative plates in a plumbing piece called a cell. As the salt water is passed through the cell, a DC voltage is applied to the plates. The salt water then splits into sodium and chlorine. Hydrogen and oxygen are produced as well and the result of all of this is the generation of chlorine to sanitize the pool. Bromine can also be generated with this system.

Q. Is there a special tank to hold the salt?

A. No - the salt is simply dumped into the pool. It dissolves and the level of salt is stated in parts per million (ppm),with systems running from 2500 ppm to 6000 ppm depending on the manufacturer.

Q. How much salt is used up in a year?

A. The salt is not consumed. The salt molecules are split into sodium and chlorine. When the chlorine is finished its work, it recombines with the sodium and become a salt molecule again. The only way to loose salt is through splash-out and backwashing the filter.

Q. Won't the salt hurt my eyes like the ocean?

A. The level of salt in a salt water pool is much lower that the ocean. In fact, the pool water will be easier on your eyes than fresh water because the salt level will be closer to the salt concentration of your tears, which is 0.9 per cent or 9000 parts per million.

Q. I am allergic to chlorine. Will this bother my skin like the water in the community pool?

A. I honestly don't know anyone who is allergic to chlorine. I do, however, know a lot of people who are allergic to chloramines, which are simply a chlorine atom bound to a nitrogen or ammonia compound. Chloramines give a dirty pool the familiar "chlorine smell". The reality is, if the pool had lots of chlorine and no chloramines, there wouldn't be any smell to the water. If a pool smells like bleach, it doesn't have too much chlorine, it doesn't have enough! Adding chlorine will destroy the chloramines and eliminate the smell that accompanies them. Salt chlorinators destroy chloramines continuously so they don't build up and produce the "typical" chlorine smell of a pool. The destruction of these chloramines makes the water much easier on the skin, eyes, and lungs.

Q. Do I still have to shock my pool?

A. There is no clear answer to this one. As the water passes through the cell, the freed-up chlorine "shocks" the water and destroys the chloramines that we were just talking about. If the bather load or the amount of waste in the pool exceeds the chlorine generation capacity of the chlorinator, you will have to shock.

Q. Will salt water rust out my pool?

A. For inground pools the answer is typically NO. For above-ground pools, the answer is typically YES. With that said, I need to explain a few things. We as Canadians know full well what high salt levels can do to metals. Our cars are caked with the stuff every winter and eventually they rust out. Your pool water will not have the same salt levels that are found on the side of your car in January. The salt in the pool is relatively low so the rate of corrosion is only slightly higher than a non-salt pool. You notice I didn't say the same. Given identical pool water chemistry, a salt water pool will be more corrosive than a non-salt pool. If the water chemistry is not kept in check, poor alkalinity or pH will be much more corrosive than salt could ever be. The good thing about a salt chlorination system is the pool chemistry will stay relatively stable. This fact more than makes up for the slightly increased corrosive effects of the salt. The reason why I differentiate between above-ground pools and inground pools is that everything has to do with construction and very little to do with actual quality of the pool. With above-ground pools, problems occur when the water is splashed out on the thin metal walls that a lot of these pools have and it evaporates. The salt solution becomes concentrated, like our cars in January, and corrosion becomes an issue. You will find that most salt chlorinator people dance around the corrosion issue because one of the great urban myths is that any salt at all will result in corrosion. The reality is that almost everything is corrosive, in one way or another. Take a look at the metal sheds that people store their chlorine in or the structures of large aircraft that are exposed to nothing more than the humidity of people breathing. Inground pools are constructed with materials and building techniques that avoid corrosion problems. Most will recommend that the pool be bonded and grounded well and fixtures such as ladders and light rings should be good quality and not aluminum. Other than that there are no issues with a standard pool. What we all need to get our heads around is that we put salt in our pools for a very good reason and that is because it feels better.

Q. Chlorine isn't healthy. Salt-water pools eliminate the need for chlorine and chemicals. Right?

A. NO. Unfortunately, there is no replacement for chlorine or bromine in our pools. Salt chlorinators generate chlorine or bromine from the salt in the pool water. The benefits of running a pool with these sanitizers far outweigh the risks of not using them. There are some very dangerous bugs out there that just love warm water. The scary part is, they also like to make us very sick. There are alternative sanitizers on the market that can ASSIST chlorine or bromine but Health Canada does not allow them to be used as a stand- alone sanitation system. Chlorine and bromine compounds - whether they come in a package or jug or are generated on-site with a salt chlorinator - are the only chemicals that Health Canada is comfortable with us using. You may have heard that there are some bugs that are resistant to chlorine and bromine. The good thing is they have never been found in pools or drinking water.

The "other chemicals" that we use in our pools are necessary for keeping the water in balance and helping to maintain the pool. Salt chlorinators will drastically reduce the need to adjust pH and total alkalinity. Their purpose in life is to generate chlorine and eliminate chloramines, so once again these chemicals are for the most part eliminated. One aspect that often gets overlooked is the "other things" in our pool. The chlorine generated by the salt chlorinator is not stabilized like the chlorine in puck form, so that needs to be added. Sunlight destroys chlorine in short order so like us, it needs sun screen (stabilizer) to protect it. The pollutants that end up in our pool are also something that a salt chlorinator has little control over. Phosphates, airborne pollution, sunscreen, and body oils often need special attention to eliminate them. There are some good and environmentally-friendly products on the market now that can take care of this for us. Their purpose is to eliminate the chemical soup that ends up in our pools without posing a danger to you or your pool. Your local pool shop will be able to help you with these natural products.

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Mark Manning is the president of Watermaid Canada Inc. of TOttnham, Ontario, the manufacturer of the Watermaid salt chlorination system for pools and a supplier of salt and salt testing products.

mark@watermaid.ca
www.watermaid.ca
1-877-987-6243