Electrolytic Chlorine Generators and Corrosion

In Blog by Timothy Petsch

Why do chlorine generators cause corrosion, especially the commercial ones?


Back in 2001 while in Minneapolis I received a frantic call from a client in Olympia, WA. This client was in the last phase of building an indoor swimming pool, and had just completed filling it up and had, in the last 30 minutes, turned the main circulation pump on. The guy was close to hyperventilation as he explained to me that he could see the metal components in the pool beginning to show signs of corrosion. He further explained to me that when he asked the owner of the commercial pool company, who happened to be on site for the startup, what was causing this corrosion, he was told that it was the TMI Salt Pure® System, and that this was the reason the pool company had been against installing a salt system in the first place!

Fortunately, my first question to him was “Can you tell me where the salt is at this moment?” His response was “In bags on a pallet by the side of the pool!” I responded “Well, that shows how powerful salt is, that it can cause corrosion while still in bags by the side of the pool!”

What this true story really is indicative of is the ignorance and rush to judgment that the commercial aquatic industry displayed in the early days of salt. In some areas of the country this uniformed bias is still going strong. So, let’s look at this issue in a transparent manner in the hopes of clearing up some confusion.

Without going into a lot of detail, in our experience 99% of corrosion (excluding that which comes from off gassing chloramines) is caused by insufficient bonding around the pool itself and in the mechanical room. Stray current can come from anywhere, including mechanical equipment that is not necessarily associated with the pool, and can run rampant through a pool with missing/insufficient bonding or an improperly constructed equipotential bonding grid. The more conductive the pool water, the more that corrosion due to stray current can become apparent. Of course, a pool with a chlorine generator will have a higher TDS, and therefore higher conductivity, than some other pools, but the corrosion is not the fault of the salt. Many liquid chlorine pools will eventually reach a TDS level (composed mainly of salt) that rivals those of salt chlorine pools. Other times galvanic corrosion, corrosion caused by the use of multiple dissimilar metals, is at fault. This typically occurs when products installed in a pool, such as lane line anchors or light fixture rings, are not specifically designed for use in an aquatic environment. Finally, there is always the potential for corrosion in a body of water with poor water balance.

I frequently hear concerns from prospective clients regarding rumors of chlorine generators causing corrosion. Most frequently the concern lies in heater failure, I have also heard statements that concrete decks will turn to mush and deck chairs around the pool will rust out if a salt system is used. I will conclude with the response that I provide to prospective clients in order to remove all doubt when this issue is raised: The big 3 pool manufacturers – Pentair, Haywood, and Zodiac – all make heaters.  They ALSO make their own chlorine generators. Were the use of these items mutually exclusive, these large corporations would not risk profits and customer ire by selling them together.

We have many commercial facilities all over the US that have been with us for over a decade with no signs of corrosion. If electrolytic chlorine generators were the direct cause of corrosion, as so many would have us believe, the product would have fallen out of use years ago.

Are we done with this association yet folks?