How to reduce the risk
Despite the risks described, there are ways to reduce the chances of damage. In pools, the least noble metal in the galvanic couple becomes the anode and assumes the brunt of damage as a result of galvanic corrosion. This process of protecting certain metals by making them the cathode in a galvanic couple is called cathodic protection.
Sacrificial anodes
Cathodic protection involves adding sacrificial anodes to the pool to become the primary line of defense against galvanic corrosion. For example, an active metal such as zinc (Zn) will be the most inclined to decay as it will become the least noble metal in the pool.
Since it is not possible to stop or prevent galvanic corrosion given the nature of how pools are built, the next best thing is to try and control any possible damage by providing a sacrificial anode to decay rather than less serviceable pool components. An inline sacrificial anode is a small plumbing fixture typically made with a zinc rod connected to a bonding lug. The zinc will be the least noble metal in the pool water and the bonding lug will provide an additional low-resistance path to ground for any currents that develop as part of the galvanic corrosion process. While the sacrificial anode will serve to provide a general level of protection for the pool system, localized anodization of components can still occur in some areas.
Additional anodes
Since most pools are quite large, a single anode located in the pump room will only protect against a portion of the total potential for damage. Adding additional anodes to the pool will increase protection; however, it is not realistic to think the more anodes added will eliminate any and all damage.
The amount and, more importantly, location of metal components in the pool system is such that it is not always possible to have anodes everywhere they need to be. Much as the name suggests, the anode metal is sacrificed in providing protection to the cathode and must be able to be replaced as it deteriorates. Zinc anodes made to connect directly to handrails and ladders, as well as zinc discs which are intended to sit in the skimmer basket are available.
Improved bonding grids
Bonding grids should also be updated to current standards on older pools where their condition, or existence, is in question. This would be applicable to most large-scale renovation projects where steel components (e.g. walls, ladder anchors, light niches, and coping) can be accessed.
Due to the general misunderstanding of how pool grounding and bonding works—especially on older pools—many were not installed correctly. Therefore, when undertaking an extensive pool renovation project, it is strongly recommended that a bonding grid system be installed, along with proper grounding of all equipment—especially if the client wants a saltwater chlorine system.
Lower salt levels
The destructive currents caused by galvanic corrosion are directly tied to the level of salt in the pool water. For this reason, using a saltwater chlorine generator that operates at lower salt levels will reduce the harmful effects on the pool. Previously, it was common to have saltwater systems that operated between 2800 and 4000 ppm sodium. Recently, however, systems have become available which operate effectively at levels closer to 1500 ppm. If saltwater chlorination is an option, consider installing low salt units to reduce the potential for pool damage.
In the know
Without questioning the validity of the product itself, the reality is, adding salt to a pool increases the potential for damage. Understanding the nature of the problem will go a long way in helping to understand why galvanic corrosion is a concern and what can be done to control it. Keep in mind, there is no silver bullet solution that will guarantee complete protection against this destructive process. This is a fact every pool owner considering saltwater chlorination should consider to make an informed decision about what is best for them and the longevity of their pool.
Steve Goodale is a second-generation pool and spa expert from Oakville, Ont. In addition to owning Green Pools and A Better Pool Company, he is also an Internet developer and author of www.swimmingpoolsteve.com. He can be reached via e-mail at swimmingpoolsteve@gmail.com.
The author should be familiar with the galvanic chart as well as fundamental electrical theory and basic chemistry and related terminology…..which is not evident in the content of these articles.
Hi Doug – thank you for your feedback. If you would like to share some sources to inform readers that would be fantastic – we are all just trying to learn. I do have a formal education in electrical engineering and a lifetime working in swimming pools though there is certainly more that I can learn. I think this article goes a long way to increase awareness and understanding of galvanic corrosion but I would agree that there is room for improvement.
Steve, from what I’ve read here (& I’ve also watched all of your videos), am I correct that a lone zinc anode attached to the ladder is not sufficient to protect the pump and heater? The pool tech that just replaced my heater believes one anode attached to the ladder will protect everything. I think I need an inline anode in the pump room to protect my equipment, and that the ladder anode will protect only the ladder. (To my knowledge, the ladder is not connected to a bonding grid – pool built in 1978 by previous homeowner, and a pool tech who knows the installing contractor has told me last year the contractor was infamous for taking shortcuts). 18×36 inground concrete. 3000 ppm salt requirement.
The deck anchors for the ladder should have been included in the bonding grid and the stainless ladder is bonded by the mechanical connection to the wedge anchor. That being said, many builders, especially older ones, float those anchors in freehand into the concrete when finishing the deck. If some part of the bonding grid would be skipped / missed this is it. The ladder anode is better than no anode however an inline anode in the pump room with a direct low resistance connection to the bonding grid would be superior. For the price of a heater vs the price of installing an anode I would not hesitate to get an inline one installed. I personally do not believe that a zinc disc provides any systemic protection for the pool.
Steve, thanks so much for your reply. My ladder slips into *plastic* cups, not metal, and at the bottom of the cup is dirt & gravel. There is no metal in contact with the ladder. The ladder already has brown streaks that look like burns which I believe to be galvanic corrosion since there were no such spots until I switched to salt 6-7 years ago. I will order an inline anode for the pump room as you suggest. Thanks again for your reply.
Hi Steve, I have an 24′ round above ground pool without a heater. Will a zinc disc in the skimmer basket suffice?
Steve – Great article and love your YouTube channel. You’ve been a huge help with the installation of our first pool. I have a 33′ round pool half in the ground. Can you recommend a few good sacrificial anodes?
There are not a lot of options on the market Tiver – basically which ones can you get in your area. Most pool stores will have perhaps one inline anode option…so that is the one you want. If no local stores have any then you can also order them from Amazon. You are already going above and beyond with an above ground pool and a sacrificial anode as most above ground pool owners do not have one installed.
Steve, great article. (From a layman, who is not fully technical) I was perusing the web, after I was in an a minor “accident”, (in a in-ground indoor pool, using “salt water” and a number of other chemicals) at a senior’s residence, where I was visiting a friend. Basically, I used the ladder, not the stairs to exit the pool. As I reached up and put my (right) foot on the second step and raised up my (left) foot to go the the next step, the lower (second) step broke (or collapsed) underneath me. As such, I heavily “whacked” my left elbow, on the metal railing of the step and smashed my right shin on the other side, as well as incurred a number of scrapes, from the falling plastic step. (It was fortunate, that I had a good grip with both of my hands and arms, so I didn’t fall forward to hit my face or mouth (teeth). After taking a few minutes to recover, I dived down to recover the broken plastic step, and I looked at the metal ladder, where the step “should” have been. There was some corrosion on the metal handles and pins and a bit on the plastic step at the side, where the plastic step would have been, if it had not collapsed on me, as I tried to exit the pool. (I took the broken step to the senior’s residence (maintenance) and explained what happened, and suggested that someone needed to check the pool, if there were any plastic fragments or metal pins in the water AND someone needed to check that ladder and the ladder on the other side of the pool, possibly more frequently for security and safety. So, with all that I have written (or said) … Based on parts of your article, Would my “non-tech” understanding be correct to suggest that “Is it possible that the “salt water” in the pool contributed to the “plastic” step collapsing underneath me and as such the senior’s residence needs to do more frequent checks on those two steps to exit the pool, in order to alleviate any additional “accidents”? Thank-You for your input.
Hi dpi Bassett. First, I am sorry to hear about your pool related accident, but very pleased to hear that you managed to avoid even more serious injury during your fall. From a technical perspective, there are a few different things happening with your comment. From experience I can tell you that rusting from the hardware connecting the steps to the rails is pretty common. This is a function of lower quality metals, combined with the close contact of dissimilar metals which causes some galvanic activity between the hardware and the ladder…but this would only result in rust staining. Even in the most extreme cases I have encountered the hardware for the steps is not structurally compromised, but more just cosmetically damaged. In your case, it sounds like the plastic of the step broke, not the metal from the hardware. Now this is something that I have seen many times before. This would be a function of aging plastic steps in an adverse chemical environment. The steps were likely weakened from both the pH of the water, as well as the chlorine content. Stress fractures would be visible before the step failed. I would guess that close inspection of the other would reveal the same. Plastic steps are common in residential pools because they are the most cost effective option. In a commercial pool I would have expected to see a high quality steel tread step. Much more durable and stable. Unless I misunderstand your comments, I do not believe the failure that you have experienced to be related to galvanic corrosion, but more likely regular wear and tear of plastic installed in a chlorinated water environment. A much stronger case could be made that improper chlorine or pH levels possibly contributing to the early step failure (if the water maintenance logs reveal any long withstanding water balance issues), or perhaps a failure to inspect equipment regularly, but I do not see salt being a main factor in either of these cases.
Steven, Thank-you for your (detailed) response. I will pass along your comments, along with my initial comments to the management of the seniors residence in Lasalle (Mtl) Quebec.
Thanks for the information. You did a great job making this concept easier to understand!
After the frustration and work of many days of throwing in shock, phosphate remover, non-chlorine shock, more shock, 25 bucks today, 50 bucks tomorrow and still almost no free chlorine reading, I told my chlorine only pool store that I was too old (73) to keep doing this and I was ready to switch to salt. They immediately told me that besides the 2500 cost to change to salt (pretty high quote from what i’ve seen) these fixtures (ladder and rails) being discussed here would corrode to the point that I wouldn’t be able to get them out. I thought it was just them scaring me to keep my business. But, from reading this, maybe there is something to it. I know it is a personal choice, but is this scary enough to keep one from choosing a salt system? Thanks for any replies.
deck anchors for the ladder should have been included in the bonding grid and the stainless ladder is bonded by the mechanical connection to the wedge anchor.