corrosive pool water: low pH pool water chemistry and swimming pool corrosion problems

Corrosive pool conditions can cause a variety of pool problems and should be avoided, by maintaining the water chemistry as close to the optimum ranges, as possible. Corrosion can result in damage to underwater metal surfaces and equipment, damage or even the destruction of copper heat exchangers, etching of masonry pool surfaces, wrinkle formation in vinyl liners and an increase in the irritability of chlorine or bromine pool water sanitizers. The corrosion of metal parts can release, into the water, metal ions that may lead to staining and/or discoloration. Corrosive conditions can be eliminated or controlled by the adjustment of the pH, total alkalinity and calcium hardness. Clicking on the underlined and highlighted "keywords" or "catch phrases," in the archived answers will give you access to additional information on that topic or product.

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► Pitting On The Pool Ladder?

The ladder on my above the ground pool is aluminum and has become pitted. What causes this and what can I do?

J. M., 6/23/2010

Aluminum, if not suitably protected by a coating, can be affected by swimming pool water. Low pH or high pH can affect aluminum. Soft water conditions and low total alkalinity can add to the problem. I don't know what the useable life expectancy of your ladder is, but it should be replaced, if there is a loss of structural integrity. There are ladders, rails and accessories made from composite materials, that are better able to resist the problematic effects of corrosion. These products are easy to maintain and do not require grounding, making installation less complicated. I hope that I have been of assistance.

Sincerely. Alan Schuster, 6/23/2010

► Ryznar Stability Index?

What is the Ryznar Stability Index and how does it help protect heaters and other equipment, from corrosion?

Austin S., 8/15/2011

An article appeared in the 8/12/11 issue of Pool & Spa News about the Ryznar Index. This index is favored, by some heater and equipment manufacturers, because it affords greater protection against corrosion, than does the more familiar Langelier Index. It favors higher calcium hardness levels and/or higher pH levels. While this will lessen the possible the corrosive effects of softer, lower pH water, it comes at a price. It boosts the calcium hardness to a point, where scale begins to form, which actually helps protect the equipment, from corrosion. However, as scale forms in the heater, it reduces the efficiency, by acting as an insulator. In a filter, it acts to cement the filter media, reducing the effectiveness of the filter. In areas of the southwest, the water is already too hard, right out of the tap and it is challenging to main a clear pool, without excessive scaling. For more information, go to this website page: Ryznar Stability Index I hope that this information will help you better protect your pool equipment.

Sincerely. Alan Schuster 8/19/2011

► Corrosion of Stainless Steels Rails and Welds?

I am the Property Manager of a condominium in Pennsylvania. The Pool that is in the building is a Salt Water, Indoor, Stainless Steel Shell with Tile over the Steel. Since day one (July 18, 2008) we are experiencing rusting around all weld joints and hand rails. The Pool Consultants are trying to say it is a "stray current" going through the pool. Although I am not an expert on Pools, I feel that the water in the Pool is not balanced. Please help, it is embarrassing to have residents swimming in a "rusty" pool. I believe it is a pH issue, perhaps also that the piping was installed with all copper instead of PVC and we lost two pumps to corrosion. I also think it has something with the air temperature inside the Pool room itself. Again, if you could be so kind and help in anyway you would be my hero!

Michelle S., PA, 3/29/2009

It could be a grounding issue and I suggest having this checked. Salt chlorine generators tend to make the pH rise, requiring regular additions of acid. High pH should not corrode copper, even if chlorine is present. The rails or welds could be of lesser quality materials and could be more subject to rusting. There are composite rails and ladders that are unaffected by the water chemistry and do not need grounding. Have the water tested for iron and copper and treat, as needed. I hope that I have been helpful.

Sincerely. Alan Schuster, 3/30/2009

► Avoiding Corrosive Situations?

We have had a salt chlorinator for 3 yrs now. The first year was good, but we had trouble getting our ladder and rails out at the end of the summer. The next year was okay but we ended up having to cut the ladder and rails off to get them out of the holes and had to buy new ones. Last summer was real rainy at the beginning of the summer season and we had a hard time regulating the pool readings. The pool light casing was totally corroded and had to be replaced and we, again, had a hard time getting the ladder and rails out. Are we the only people who have had these problems? Our pool company hasn't had many suggestions for us and said they only have a couple of customers with these types of problems. Any suggestions? Thank you.

Lori H., Michigan, 5/19/2009

Due to the drastic increase in the cost of nickel during the past several years, stainless steel has become very expensive. Manufacturers have attempted to save by using lower grades of Stainless (less nickel), thinner walls (less material), and by importing from China. China is currently the main source of stainless steel pool rails sold in the US. They are inexpensive, but for the most part of inferior quality. That, combined with the increase in popularity of salt chlorinators has led to many problems. You are not alone by any means. I realize this is no consolation.   Pools that are over 15 years old are less likely to be affected, as the quality of rails and ladders installed at that time was superior to those that are on the market now. The older ones are. therefore. less affected by salt or chemicals. Unless one specifies marine-grade 316 Stainless Steel (which is expensive and NOT the standard), a salt-chlorinated pool that uses steel rails is very likely to degrade. In the fine-print on the warranties of most stainless steel rails and ladders, they all but guarantee that their rails will corrode, if chemical balance isn’t precisely maintained at all times. The above applies to any steel products in pools. Most fittings and pool accessories are now made of plastics, but rails, ladders and a few accessories like rims around lights are holdouts. The only solutions are to either

A:         Maintain PRECISE chemical balance in your pool at all times.

B:         Change your steel rails or ladders for a non-steel alternative.

C:         Find a manufacturer that can provide 316 Stainless if you prefer the look of steel.

D:         Expect to have to continue replacing your ladder every two or three years.

Corrosion is not limited to pools with salt chlorine generators. Even pools, using ordinary liquid chlorine, will have salt content that can rise quite high, after just a few years. The key factor is to avoid corrosive chemistry, avoid having two dissimilar metals in immediate proximity to one another and choose a quality alternative, such as rails and ladders manufactured of composite materials. I hope that this information will be helpful, in understanding the problem and making the right choice.

Sincerely. Alan Schuster, 5/19/2009

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► Copper & Heat Exchanger Corrosion?

Alan, my copper level at closing last winter was 0.5 ppm, measured with a test kit. This occurred when my second heat exchanger dissolved into the pool water. (Long story - installer paid for his error and replaced second heat exchanger). No copper ever added to pool on purpose (i.e. no copper-based algaecide). After the first heat exchanger was dissolved (like I said, a long story), the entire plaster pool surface was stained blue-green. Drain, acid wash, refill. Stain gone (all at installers expense - at least he's honest). Now we're on the second round. Problem root cause fixed, 3rd heat exchanger now in place, but, as I said, 0.5 ppm copper remains from dissolved heat exchanger number 2. Question: What's the best way to get rid of the copper? I'd rather get rid of it than sequester it. Naturally, I'd like to avoid another drain and refill. I've heard that there are products that can remove copper. Have you had any experience with this? pH is always on the high side, around 7.6. I'm afraid the copper is going to precipitate out any day now. My wife says she can see little green spots on the white plaster. My eyes are not that keen, but I want to nip this in the bud! I'm a scientist and an engineer, so I like to know what's going on, even if I let someone else do the work! Also, my installer, though honest, needs some direction. Thanks for your advice!

David S., Colts Neck, New Jersey, 4/25/2011

That's quite a story. Sounds like someone put a chlorinator in front of the heater and this resulted in the corrosion of the copper heat exchanger. The only way to deal with the copper is by chelating the copper. This will complex the copper and allow it to remain in solution, thereby avoiding the risk of precipitation or discoloration. Mineral Treatment products use the term "remove" in a very general sense. They actually mean "helps control." These products do not physically remove the copper. A concentration of 0.5 PPM is comparable to that of a copper algaecide. By adding a quality mineral treatment you should be able to complex the copper and avoid problems. Because this product will chelate all of the heavy metals and to assure that enough product has been added, I suggest that you add a double or triple dose. Thereafter, add an initial dose each springtime opening. Allowing the pH to remain at 7.6 or above, decreases the solubility of copper and increases the likelihood of staining and precipitation. To better assure proper overall pool water chemistry, visit a pool store that has a very reliable, professional lab such as a WaterLink or Pinpoint system, rather than a less accurate test kit or strip reader. To locate a dealer near you, go to: LaMotte Professional Testing Center Locator I hope that I have been helpful. Enjoy the season and the heater.

Sincerely. Alan Schuster, 4/25/2011

► Rising Salt Level?

I recently bought a Tracer PockeTester, from your website. I am quite satisfied, with the convenience and reliability of the tester, which I use to monitor the salt levels in the pools, on my service route, that have a salt chlorinator. While I like the convenience of a salt chlorine generator, I never got around to putting one on my pool, in the 3 years since it was built. I use a combination of a trichlor feeder and lithium shock. For no other reason, other than curiosity, I tested the tap water and found a salt level or 600 PPM. That is not uncommon or unexpected in this area. I then tested the pool water and found a salt level of 2000 PPM. That came as a major surprise, since I have never adding any salt. Is there an explanation?

Stephen S., 6/30/2010

Evaporation!!!! Finding high levels of salt or TDS is nothing new and affects most pools, that are a few years old. Assuming that you have a typical inground pool, you can lose 2-inches of water a week. Possibly more, in the summer, in a hot dry location. That 2-inch loss represents 2-3% of the water volume, depending on the presence and size of the hopper area. Even allowing for rainfall to replenish 1/2 of the lose, you are still adding about 10 PPM of salt, every time, you top off the pool, with the water containing 600 PPM of salt. 10 PPM a week, for 3 years, and you can easily reach 2,000 PPM of salt: almost as much as some pools with salt chlorine generators. Pump outs, splash outs and backwashing will slow the rate of increase, However, no matter what the salt level will rise substantially, over time, when you are dealing with water than contains 600 PPM of salt. If you were to use liquid chlorine the rate of salt increase would be even higher. Measure your own average weekly evaporational water loss and calculate the % lost. Multiply this by the PPM of salt content of the new water and you have the weekly rise in salt. You don't have to have a salt chlorine generator to end up with salt in the pool. The levels are not enough to taste, so it goes by unnoticed, so long as the overall water chemistry is good. If the pool did have the salt chlorine generator, with water containing the appropriate amount of salt, the levels would rise even more. When the salt level gets too high, water should be replaced. Thank you for writing an for encouraging me to put it to the numbers test.

Sincerely. Alan Schuster, 7/1/2010

► Salt Corrosion?

I am a pool builder and am totally sold on salt chlorine generators. They are great. However, there is one sticky point I need to clarify with my potential customers. Corrosion. As I am located in Toronto Canada, we use salt on our roads in winter and it rusts our cars over time. Everybody knows it. I know that the levels are much higher than in a pool. Can you please provide me with some data on the corrosive elements of a salt chlorine generator, so I can answer these objections. Any help would be greatly appreciated. Thanks.

Bill D., Toronto, Ontario, 3/4/2005

The parts of the cars that rust are made of ferrous metals (steel) and possibly some other metals or alloys. There is no doubt that salt will have a negative effect on cars. However, pools are not made of ferrous metals. The salt add to a salt chlorinated pool will only result in corrosion, if two dissimilar metals are in immediate proximity to one another. Without this relationship being present, there will be no corrosion due to the salt. Even pools without a salt chlorine generators present, can have significant levels of salt and TDS. Relentlessly, evaporation causes salt and TDS level to rise. Pump, filter and accessory manufacturers have long known about this problem and the newer products are designed with the thought that a salt chlorine generator might be in use. If the pool walls are steel, the liner separates the water from the steel. Gunite pools have finishes that are salt water tolerant and fiberglass pools are completely unaffected. If the ring on an underwater light is stainless steel and the screws that hold it in place are chrome-plated brass, they will completely dissolve over time. If the screws are stainless steel, there is not longer a corrosion problem. The overall pool water chemistry must be maintained within the accepted parameters, as with any pool. Testing the salt level helps to get proper performance and helps assure longer life for the salt-cell. I hope that I have put your mind at ease.

Sincerely. Alan Schuster, 3/5/2005

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► Corrosion Concerns?

We are in the market for a pool. We are trying to find out the facts on saltwater vs. chlorinated pools. We had one guy trying to sell us a saltwater pool. We were told by another pool builder that they love saltwater pools, but stopped building them because the water was eating up the coping.

Shawn M., 4/17/2007

There are millions of pools with salt chlorine generators out there and all have coping, of various types. My first Lectranator salt chlorine generator usage was nearly 25 years ago. Possibly, there are some types that do not fare well with salt chlorinated pools or any water with high total dissolved solids (TDS. Some natural stones could be ill-suited to use in any type of pool and should be avoided, unless properly sealed against the elements. The problem is that natural stones can vary considerably, even when the names are the same. You are only adding 2500-3000 PPM of salt: ocean water is 15 times higher. Some of the water in Arizona and elsewhere contains 1500 PPM or more, right out of the tap. A five year old pool on regular chlorine could easily top 3000 PPM. High levels of chlorine, which salt chlorine generators help avoid, is usually even more damaging. I suggest discussing this with the builder. Choosing a pool built of the right materials should eliminate problems. It is easier to use and control, as compared to standard chlorine products and that accounts for its huge popularity. About 90% of pools in Australia, where salt chlorine generator originated over 30 years ago, have these units in operation and they use coping, decking and everything else. Some coping, decking and stone features may have to be sealed, with an appropriate product, to protect them, not only from the effects of salt, but from the effects of pool water and the elements, in general. I hope that I have been helpful.

Sincerely. Alan Schuster, 4/17/2007

Editors Note: The following information is from someone that I hold in high regard and is being added to help shed more light on this subject.

My name is Sean Assam, with AquaCal AutoPilot Inc. I've been in the industry for 20 years and have been exposed to almost every facet of the pool industry. I am CPO certified. I instruct classes in Water Chemistry and Testing Methods, Pumps and Filters, and our own "Pool Pilot Flight School" (all of which are approved continuing education credits, required for Florida contractors). I was the Technical Support Manager and R & D director for the last 5 years at AutoPilot. Currently I do the Commercial sales and support for Aqua Cal (Heat Pumps) and AutoPilot. So now I'm dealing with large commercial systems on small and large public pools, such as the Ritz Carlton Resorts, Hyatt Resorts, Four Seasons, Marriott Hotels, etc. I'm sure if there were real issues, these major facilities would not even consider salt as an alternative to sanitizing their pools and spas.

For years, it seems that everything that has occurred negatively to a pool has been blamed on salt systems. It really does not matter that these same issues have been around much longer than salt system, but salt has been the convenient scapegoat. I'm not sure what may be causing the coping or deck damage, but in my opinion, these problems are regional and most likely have to do with the quality of the deck material (limestone quarry) and cement mixture.

The contractors are mostly in Arizona and Texas. And while the materials they use there are similar to materials used nationally. It makes sense that even from the same quarry, the quality can vary from high grade to low grade. If this were a salt issue, the problems would be of national scale. Salt systems have been around in the US since 1984, even longer in Australia (1960's). Prior to AutoPilot purchasing this company from The Olin Corporation, we were a distributor of the Lectranator salt system. We've sold several thousand systems in South Florida alone and I cannot think of a single deck damaged pool that was contributed to the salt system. Since we purchased the company in 1992, we've sold over 100,000 units nationally, and another 50,000 units internationally. That's just one manufacturer in the salt chlorination industry. Combined, there are over a million salt systems installed in back yards all over the US. Certainly, this would be a national epidemic, if it were damaging. Yet, we're not seeing this, but on a few isolated cases. I can say that none of these contractors, having damage to their customer's pools, were AutoPilot dealers. If so, I would have been personally called out to investigate the problem. That's not to say that we're much different than the others. Salt systems all operate in a similar manner. I can say though that salt systems are being unfairly blamed for these long standing issues. Some natural materials are inappropriate to use with any pool and others should probably be protected with a sealer.

Best Regards. Sean Assam, 4/18/2007

► When To Replace Copper Pipes?

You've answered some pool questions for me before and I trust you so I wanted to get your opinion on this. We are getting estimates for new plaster and possibly new pool decking right now. I was just told that we need to replace the copper pipes with PVC before re-doing the decking because copper will only last about 30 years (our house is 40 years old, swimming pool at least 30 years old) and they will start leaking soon and consequently ruin the decking we put in. Is this true? Appreciate your time & feedback.

Karen C., 2/11/2009

I don't know if you can assign a finite life to copper pipes. Your contractor is trying to convince you to spend some money now, while new decking is being installed, rather than risk a much greater expense down the road, should the pipes fail. In that respect, he is making you aware and allowing you to decide. Thirty years might be reasonable, but so much depends on how the pool was maintained. If the pool was allowed to remain in acidic conditions, with chlorine present, copper corrosion WILL occur. The longer these conditions persist, the more corrosion occurs. If a trichlor feeder was placed up stream of copper pipes, corrosion could result. I assume that you have not owned the pool, for these 40 years, and maintenance questions are unknown. If it were my decision, I would opt to replace the pipes. PVC pipes would allow you to use a salt chlorine generator, if you so decided. With copper pipes, the salt might corrode any soldered joints. I hope that this information is helpful.

Sincerely. Alan Schuster, 2/11/2009

► Why Not A Low pH?

If chlorine works better at lower pH readings, why not keep the pH lower than 7.2-7.6?

Anonymous, 5/3/2003

Chlorine does work better at a pH below 7.2. However, there are consequences that will result. Corrosion can present a problem below 7.0. As the pH falls below 7.2, chlorine can become increasingly more aggressive and irritating. The pH of the eye fluid is 7.6 and, as you move further away, discomfort can increase. Depending upon the type of pool - vinyl lined or masonry - corrosive low pH conditions can cause surface etching, liner wrinkling and equipment damage. A pH of 7.2-7.6, helps assure bather comfort, allows effective sanitizing and helps avoid corrosion. I hope that I have answered the question.

Sincerely. Alan Schuster, 5/3/2003

► Pool Liner Wrinkles?

When my vinyl liner was installed a few years ago, it nice and smooth. Today, I see some wrinkles in one area. What's the cause?

Barry D., Cinc., OH, 7/13/2004

Two things come to mind. It is possible that the bottom has undergone some shifting and/or settling over the past few years and this has led to some wrinkling. Another possibility is that corrosive, acidic water conditions have caused the vinyl liner to increase water absorption and this has led to a stretching of the liner and the wrinkles. Is it possible that you have been keeping the pH too low? It is important to maintain the pH in the 7.2-7.6 range for bather comfort, sanitizer efficiency and to help protect the pool equipment! Low pH can be quite common with the use of trichlor tablets in an automatic chlorinator because the product is acidic and requires regular pH monitoring. Because the water looks good, many people tend to neglect the pH. The practice of "dumping" in chemicals and allowing them to remain on the bottom, for prolonged periods, is not recommended. Acidic chemicals such as pH decreaser, muriatic acid or cyanuric acid can create the acidic conditions that can contribute to this problem. Always take care to broadcast or distribute all chemicals, so as to avoid local high concentrations and lessen the likelihood of problems. I hope that I have been helpful.

Sincerely. Alan Schuster, 7/13/2004

► Rough Surface, Grayish Color & Hives?

We have a gunite pool that was installed last Spring (2003), and have had a company servicing the pool since then. Our plaster has gotten rougher, and is pitted around some of the marker tiles. Is this normal aging (in one year) or what would be likely causes? Also, we have areas in the plaster that have been grayish since installation, but the pool company said that was normal, what do you think? Last, my children and my husband have experienced a hivish sort of rash, with extreme itching, the last few times they were in the pool/spa, but the pool serviceman said nothing he put in should cause that. Any ideas? Thanks.

Brenda P., 5/3/2004

It sounds like corrosive water conditions: low pH. That would explain the pitting and roughing up of the surface. If you have a heater, it could also explain the graying of the surfaces. Acidic water conditions cause chlorine to be more aggressive and irritating and this fits it with what you are describing. If your pool is being maintained on slow dissolving chlorine tabs in a feeder, it sounds like little or no attention is being paid to the pH. Have the pH total alkalinity and calcium hardness tested. If you have a heater, have the water tested for copper and add a couple of doses of a quality metal treatment at least 6 hours before raising the pH. Proper chemistry won't repair the surface, but should prevent a further worsening. No, this is not normal! Hope the information helps.

Sincerely. Alan Schuster, 5/3/2004

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