Do you have metals in your tap water? Have you ever filled a pool and had the water get discolored when you added chlorine for the first time? If so, do you know why that happened? And more importantly, do you know how it can be prevented?

Dissolved metals are commonly found in tap water

Source water is different everywhere you go, which is why we insist on testing tap water before filling a pool, or even servicing the pool. If you don’t know what is coming out of the tap, you will be at a severe disadvantage when it comes to managing pool chemistry. Since most pool operators test only a few factors–pH, total alkalinity, chlorine, and sometimes calcium hardness–otherwise predictable problems occur. To really grasp what will happen to the pool, one must know what is coming out of the tap.

If you have ever seen discolored water, or pools with metal stains, that’s an obvious sign of metal content in your water. Iron, when oxidized, turns brownish or orange in color. Stains will be ugly and visible to anyone looking. Copper has more of a light green, or even turquoise look to it when it gets oxidized. Manganese has a dark color, between black and purple, depending on the severity. It is also not uncommon to see a blend of multiple metals for unique colors and stains.

What causes metal stains and discoloration?

Metals are usually the first contaminants in water that chlorine oxidizes. This has to do with chemistry and the ease of oxidation. Here is a chart that shows the breakpoint chlorination curve, and it starts with the first thing chlorine attacks: metals.

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Metals like iron, manganese and copper are often the first things oxidized by chlorine.

The chart says in the first section “Destruction of chlorine residual by reducing compounds.” In this case, metals are the reducing compounds, because they get oxidized. Being oxidized means metals lose an electron and take on an oxygen from the oxidizer (chlorine, either HOCl or OCl-). After metals have been oxidized, at the expense of some of the free available chlorine, chlorine then begins to oxidize non-living organics and nitrogen compounds that form combined chlorine.

But let’s get back to metals. When metals are oxidized, they become a new substance altogether. It is usually with oxidation that metals become visible because of their color. Purely dissolved metals that have not been oxidized are normally invisible in water. In other words, oxidation of metals brings out their color in water.

Can metal stains be prevented?

Metal stains in pools can be prevented. The way to prevent metal stains is to control metals. There are a few ways to control metals, but for the purposes of this article, let’s stay with what is practical in the pool business: removal, sequestration, and chelation.

How to remove metals from water

With certain types of filter media, metals can actually be filtered out. Such products do exist, but they can be costly. One such example is reverse osmosis, which takes just about everything out of the water…metals included. There are specific metal trapping filters that can be attached to hoses and plumbing that target heavy metals specifically as well. Some pool filters can also trap metals if they have a small enough filter media. Even so, with the help of certain sequestering agents, filters can capture metals to be backwashed or removed from the water.

If your metals are very high, removing them is a good idea. The less heavy metals you have in your water, the easier to manage.

Metal sequestration

Sequestering agents are common in the pool industry. Sequestering agents work kind of like a ‘metal magnet’, which attract metal ions into a cluster. When the electrons bind to the sequestering agent, oxidation of those metals can no longer occur, which is great! Sequestering prevents metal stains and discoloration of water. That being said, the metals are in suspension, and still in the water. The good news is, sequestered metals can more easily be caught by a filter and removed.

The challenge with sequestering metals is that most of the sequestering products are some kind of phosphate-based acid. Phosphonic acid is the most common type, and it is used even in municipal water treatment systems. Sequestering metals protects infrastructure and can also prevent scale in water treatment pipes. Normally this would be no big deal, except that phosphonic acid is basically liquid phosphates, and food for microorganisms like algae. So pool operators now have elevated phosphate levels to deal with.

What do you think happens when the pool operator uses a phosphate remover? The sequestering agent is wiped out, and the metals it was holding are now released back in the water, and available to be oxidized once again. The use of phosphate-based sequestering agents, therefore, should be used either temporarily for metal removal, or at least with the knowledge of their impact on phosphate levels.

Metal chelation

Chelation is similar to sequestration, in that it binds with metals and prevents oxidation (and metal stains). Unlike a sequest, which binds many metal ions together into a cluster of sorts, a chelant grabs individual metal ions. No clustering, just individual metal ions that have been chelated separately.

In our far-from-scientific lingo, we think of it like this: sequestering agents cluster metals and hold them in suspension; chelating agents grab individual metal ions separately and hold them in solution.

Our Metal and Scale Inhibitor (MSI) is an NSF-50 Certified chelating agent. It is not phosphate-based, and therefore compatible with phosphate removers. MSI is great at preventing stains and discoloration because it holds metals in solution and protects them from oxidation. That being said, MSI is not meant to be used to remove metals. When you hold metals in solution, they may pass through filters, unlike clustered metals bound to a sequestering agent.

Prevention is easier than Correction

“An ounce of prevention is worth a pound of cure.” – Benjamin Franklin

You can remove, sequester or chelate metals before they are oxidized. If you do, metal stains should not occur. Be sure to test tap water to know the metal content, so you know how much is being introduced on a weekly basis when the pool is replenished with water. Once stains begin to form, it may take citric acid to lift them off the surface, and that process is aggressive on plaster.

We hope this article helps you better understand metals, and gives you hope that yes, you can prevent metal stains and discolorations in your pool. If you have specific questions, contact us or your local NextGeneration Dealer.

Meaningful pool care in more ways than one

Think of the most dynamic pool chemical you know of. What does it do? When we think of the word “dynamic”, it suggests multiple uses and a range of positive results. Metal & Scale Inhibitor (MSI), to us, is one very dynamic pool chemical. It serves many functions, including the ability to both prevent and undo common problems in swimming pools and other water treatment systems. Let’s share some of them.

1. Preventative water chemistry

Water chemistry affects everything in a water system. If your water is corrosive, it can cause damage to surfaces and equipment. Conversely, if it is scale-forming, the scale itself can cause damage too; pipes with scale in them can increase water pressure and reduce flow rates.

The most important factor in preventing corrosion and scale is LSI balance. After that, it helps to have a chelant like MSI to hold minerals and metals in solution. Take calcium carbonate scale, for example. If calcium is held in solution by MSI, it takes a much more for scale to form. Think of MSI as allowing more grace to your water chemistry.

It’s not that MSI prevents these problems from happening…it’s that it gives you, as an operator, an advantage in handling minerals and metals.

2. Protecting pool plaster

Pool plaster is most vulnerable while it is curing. Plaster curing can take 30 days more more while the surface hydrates underwater and hardens. Given that calcium chloride is often used as an accelerant in plaster mix, it provides available calcium to water that is probably calcium-deficient. Water will stop at nothing to reach equilibrium. As the universal solvent, water dissolves whatever calcium it can find and bring it into solution for its own benefit; the most readily available source is plaster or tile grout.

But what about vinyl liner pools, or fiberglass? The LSI still applies, but the difference is water has no source of calcium. Therefore, low LSI water corrodes its way through everything trying to find it. The damage can be severe over time. For vinyl liners, this can mean fading, wrinkling or even wearing through the liner itself, allowing water underneath it. It’s no good.

MSI provides more grace to the LSI. In effect, it seems to buffer the LSI acceptable range, making it more difficult to form scale, and more difficult to corrode. Of course, this buffering benefit has its limits. At some point, the LSI can be so far out of range that no amount of MSI can stop the inevitable consequences. Use MSI immediately upon filling (and refilling) a swimming pool. It gives you more time to adjust the chemistry to get in proper LSI range.

3. Dechlorination

With any sequestering agent or chelant, one of two things happens: it gets oxidized by chlorine, or it wipes out chlorine. MSI’s initial “purge” dose wipes out chlorine. In most cases, this is an annoyance; chlorine must be hand-fed for two or three days to catch up, because otherwise the pool is unsafe. Fortunately, the weekly maintenance dose of MSI is small enough that it hardly has any impact on chlorine levels. More importantly, the good news about MSI is it will not be oxidized out of the water by chlorine. That means it stays in the water and works to your benefit over a longer period of time. It’s just the initial concentration of the purge dose of MSI that overpowers chlorine…and when dosed properly and evenly circulated throughout the pool, chlorine levels can maintain just fine.

Dechlorination is sometimes needed, however. For example, if you need to do certain types of maintenance, or bring chlorine levels down from recent hyperchlorination, MSI can help. Rather than using sodium thiosulfate, MSI can accomplish more than just lower chlorine. After all, you get the benefits of this dynamic pool chemical while lowering the chlorine level to where you want it.

Realistically, dechlorination is a rare need for swimming pools…but sometimes it’s urgent. MSI can drop chlorine levels down in just minutes.

4. Chelating Metals, Preventing Stains

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Metals are the first things to be oxidized when chlorine is added to water.

Metals are the first substances to be oxidized when chlorine enters the water. Oxidation can change the color of certain metals. Eventually, when the water is oversaturated with dissolved metals, or when they are oxidized, they can fall out of solution and stain. Just like with calcium saturation, water can only hold so much.

Stains come in many different colors, and there are entire businesses devoted to stain removal. We are not one of them…but again, MSI is a dynamic pool chemical. Just like with calcium, MSI gives more grace to the water’s ability to hold metals in solution. With MSI in your water, metals have a far more difficult time coming out of solution and staining, because the metals are chelated.

Chelating metals means MSI isolates each metal ion and binds with them. Binding with metal ions prevents them from being oxidized.

rebar staining, pool stain, plaster stain

When stains originate from behind the plaster, the stains will continue to occur. MSI cannot prevent these types of stains.

Can MSI remove existing metal stains?

Over time, MSI has shown it can gently dissolve stained metals back into solution and lift them from the pool surface. We told you MSI is a dynamic pool chemical. Unlike acid-based products, however, this process is slow. You may want to combine its efforts with ascorbic acid (vitamin C) to speed up the process. That said, be sure that the stain in question is, in fact, caused by metals in the water. Some stains come from behind the pool surface itself, like rebar being too close to the surface. In those cases, MSI cannot prevent or permanently remove that problem.

5. Scale removal

Yes, just like removing stains, MSI can dissolve calcium back into solution as well. Of course, the long-term solution is LSI balanced water…but even then, hardened scale won’t move easily. MSI is the chemical to soften and remove scale deposits around your pool. It can even remove scale on spillways and water falls, as long as the MSI-treated water has time to affect the scale area. Raise your water level to remove scale on a tile line, for example.

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In a matter of weeks, MSI gently removed carbonate scale from this pool’s spillway. In addition, this pool used AAD enzymes. Look at the difference in water clarity!

Why use one dynamic pool chemical vs. multiple single-use chemicals?

Why not?

Posts

How to prevent metal stains and discoloration in swimming pools

Dissolved metals are commonly found in tap water

What causes metal stains and discoloration?