Salt Water Swimming Pools

by Mark Manning
President
Watermaid of Canada Inc.

After preaching the benefits of salt chlorination systems and trying to dispel the myths and misconceptions with these units, I realized that one on one sales meetings and phone conversations, although effective, simply didn't get the message out to the masses that were naively accepting or rejecting this technology. I soon concluded that I needed to sit down and take the time to put one of my sales meetings into written words that would go out to more than sales managers and pool builders. The public at large needed to know a lot more than they were being told and if I didn't take the time to write this article, no one else would. At the risk or putting even the most curious reader to sleep, here we go with my version of "why buy a salt system for my swimming pool, and what should I know".

To start off with, I think that we should understand some basics of how these things work.

A salt chlorinator consists of a power pack and a cell. The cell is always located in the plumbing after the pump, heater and other equipment. The cell is simply made up of a cathode and an anode, which is powered by the (you guessed it) power pack. There are different ways of arranging the anode and cathode, and manufacturers have patented the way that their cells are made or controlled. For the sake of simplicity, let's just stick to the idea that all cells have an anode and a cathode. When current passes between the cathode and the anode, it splits the salt molecule, which is in the water. When the salt, which is sodium chloride, splits, it frees up a sodium atom and a chlorine atom. At the same time hydrogen and oxygen are being freed from the water (H2O). Now before I ramble on too long and you roll your eyes and move on to something else, let me simply say that the cell produces sodium hypochlorite from this splitting of molecules. Sodium hypochlorite is the same stuff that you buy in the jugs at the pool shop. We just make it ourselves on site. Like most things home made, there are no additives which the chemical companies put into the jugs of chlorine to keep them from going funky before you get them home.

There is nothing special about the pool or the equipment used to run the pool. Pumps filters and heaters are all the same. Retrofit of an existing pool to a salt system is relatively simple as long as there is enough room to install the cell. Some manufacturers design their cells and their installation for tight quarters while others consume an enormous amount of space. To convert our pool from an old fashioned chlorine pool to a salt pool is as simple as adding salt to your pool water. Yes, that's right you simply dump bags of salt into the pool, and let them dissolve. How much you add depends on the brand of salt chlorinator and how "comfortable" you want the pool to be. There is a lot of misinformation out there about salt levels and corrosion. To be absolutely honest, the more salt you add to your pool, the more corrosive it becomes. With that said, you need to understand the salt levels that we are talking about here. In salt pools, we are talking about a range of 2500 parts per million (ppm) and 6000 ppm. 6000 sounds like a big number until we realize what that is. 6000 ppm is 0.6 %. That's right just a little over ½ of 1 percent. Compare that to sea water that is about 35000 ppm or 3.5%, and you start to see the levels that we are talking about here.

So who uses different salt levels and why wouldn't they all agree on a level and go with it? This is where the pool industry can't seem to come to grips with a standard. Like control systems everyone seems to have gone off on their own tangent and for their own reasons and beliefs, have set their own standard. Let's take a moment and see if we can understand the applied logic. The low (if you can really call it that) salt manufacturers argue that their systems are less corrosive and save money on salt. The higher salt manufacturers argue that the difference in corrosion effects when going from 0.25% to 0.6% is laughable. They also argue that the higher salt level is more comfortable to the pool user and the salt chlorination systems have a much easier time maintaining residual chlorine levels. As a general rule, the Australian salt chlorinators tend to push a higher salt level while the North American manufacturers tend to push a lower level. The Australian argument is that they have been using salt chlorination systems longer than anyone else in the world (35 years in the case of Watermaid) and if corrosion were such an issue, they would have ceased to exist a long time ago. No worries or not, people will not buy a product that doesn't work or will damage their property. At least not more than once and the Australian market is mature enough to have gone through several life cycles of these units.

Another myth that seems to be floating around out there is that

"Salt chlorination systems are chemical free."

The truth is, salt systems produce a chemical compound, which is necessary to sanitize your pool. In fact it produces one of only 2 chemicals that are recognized by Health Canada as a way to safely sanitize a swimming pool. Those are chlorine compounds and bromine compounds. Some salt systems can even generate bromine but I'll leave that for another article.

Before we leave the thought of salt systems not being chemical free, it would probably be good to understand where this myth comes from.

First of all, chlorine generated on site by a salt chlorinator does not need chemical stabilizers and other chemicals that manufacturers of bottled and granular chlorine need to add to their packages. These additives tend to drive the pool Ph and total alkalinity off as well. When this happens, chemicals are required to bring the Ph and total alkalinity back in line. With a salt chlorinator, the pool solution is balanced and since you generate the sanitizer from that balanced solution, the pool Ph and total alkalinity tend to remain constant. The only things that can drive the pool balance off are the things that jump, or fall into the pool.

So can a salt chlorination company claim that their chlorination system is a chemical free way to sanitize your pool? Of course not! Can they claim to drastically reduce the chemicals required to maintain your pool? I guess we would have to give them that one.

The last little bit of chemistry that I will force onto you is the salt itself. A common question is, "How much salt will I need to add to the pool in a season?"

The answer is; how much splashing will be allowed in the pool?

The salt is not consumed in a salt pool. When the salt is split to form the sanitizer for your pool, the "chlorine" which is generated, attaches to the gross stuff in your pool. If it can't find anything bad to attack, it will recombine with the free sodium in the pool solution and become a salt molecule again. If it does jump on some bad guy in the pool, it will hold him until it goes back through the cell of the chlorinator where high concentrations of generated chlorine will oxidize the bad guy and free up the chlorine again. This is another advantage of a salt chlorination system. There is a constant generation of sanitizer and a constant super chlorination effect within the cell, which prevents a buildup of combined chlorine in the pool. This combined chlorine (mono, bi and tri-chloramines) is what gives a dirty pool its characteristic strong chlorine smell and it is also what makes peoples skin itchy and red and contributes to burning eyes. These complaints are typically non-existent in a salt pool.

The only time that you will need to add salt to your pool is after you have backwashed a few times, when you fill the pool in the spring or when you and the kids have splashed a lot of water out of the pool. Salt is not lost due to evaporation. It is left in the pool.

So if a salt chlorinator generates chlorine, why is everyone raving about them? The answer is convenience, economy and the feel.

Convenience: You don't have to dump chlorine in your pool. This is a great thing for people who have pools at the cottage or summer home. It is also nice to be able to go on holidays for a week or two and not return to a green slimy mess.

Economy: On average, it costs about $400.00 per year for chemicals for your pool. Some spend more, some a little less, but the average is around $400.00. Most good quality chlorinators will pretty much pay for themselves within the warranty period offered.

Feel: This is the one that is the hardest to explain. When we first heard about salt pools, most of us thought about swimming in the ocean and that sticky feeling we got when the seawater dried on our skin. The salt levels used in salt pools are a lot less than that found in seawater. Ocean water is around 35,000 parts per million salt. Salt levels in salt swimming pools are between 3,000 and 6,000 parts per million depending on the brand that you choose. Some units are damaged by higher salt levels while others are designed to operate at higher levels without voiding the warranty.

The next question is, how does this make the water feel more comfortable?

Well, you asked for it; our body chemistry has a salt level of 9,000 parts per million. If you remember your high school biology, you may recall osmosis and how solutions try to balance themselves across cell membranes. If you weren't paying attention that day, it can be summed up simply (yes I know that it is a little more complex than this) by saying that a salt solution will try to balance itself. If we jump in the ocean, the salt concentration in the ocean water is 35,000 parts per million. The salt concentration in our body is 9,000 parts per million. For simplicity sake, let's say that the salt is prevented from moving through the wall of the cells in your body but water can move. Think of it like a screen door in the summer time. The nice breeze can move through but the bugs are too big to get through. So here we are standing in the ocean wondering what is happening. Well, the solution in your body is trying to balance with the solution in the ocean and it won't stop until they are in balance. The salt can't move but the water can, so the water in our body moves into the ocean water to try to get our body's salt solution to 35,000 parts per million. Most of the time we don't even notice this dehydration of our bodies.

Now if we take a salt solution that is close to our body's salt level, there will be very little movement of fluids between the pool and our bodies. A regular pool has very little salt so the water is forced into our bodies causing the well known wrinkling of our fingers and toes. It is also another reason for the discomfort of our eyes when we open them in a regular pool. With a salt pool, there is little to no fluid transfer so the water feels more comfortable and our eyes don't sting. Salt also has a natural softening effect on water, which makes the pool feel even better.

There are a number of options available on salt chlorinators today. Some have salt level indication; some have ph indicators, digital displays and pc links. Others have stayed away from complicated systems and sensors to improve unit life and reliability. For the pool owner, you need to decide what you really want and need on your system. With complicated systems, there is often a trade off in warranty but then again, you may think that those extra toys on the chlorinator are exactly what you need. The best advice is to shop around and understand the advantages and disadvantages of the units available.