How to Remove Metal Stains in Your Pool—And Keep Them Gone

Listen, there’s nothing wrong with wanting your pool to look great. And when you spend so much time making sure that your waters are sparkling clean by choosing the perfect pump, properly chlorinating your pool, and so much more, it can be irritating to see that somehow it’s still accumulated dark metal stains. Okay, so those smears won’t actually be harmful to swimmers. But they’re still an eyesore—and by the way, they’ll only get more difficult to remove with time.

Thankfully, removing metal stains is much more straightforward than figuring how on earth they appeared in your pool—though we’ll also figure that out, too. I’ll explain how to determine whether that stain is really caused by metal, how to get rid of the stain, and how to prevent it from returning in the future. The result? Your understanding of metal in your pool is going to be iron-clad.

Is That Really a Metal Stain?

Pool stains are caused by one of two possibilities: either organic matter like berries and leaves, or metal. One quick way to determine if your stain is in fact metal is to rub a bit of ascorbic acid on the stain—vitamin C tablets you might already have lying around should work great. If the tablets remove or at least lighten the stain, you’ve got metal on your hands. And if you’re ready to get serious about understanding the stain, you can determine what kind of metal has invaded your pool based on its appearance. You know what they say: judge a stain by its color.

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Copper 

Copper usually stains a green, blue-green, or blue-green-black hue. These stains usually happen when your pool is being filled by well water, or if you have copper plumbing that has corroded. Metal parts and equipment might also be the culprit. 

Iron 

Iron stains a green, red-brown, and green-red-brown hue. Again, well water might carry high concentrations of iron. But another reason for the introduction of this amount of iron into your pool is even more surprising: if you have a rusting iron fence or anything else made with iron around your pool, a heavy rain can expose it to your water. One significant case of this that I’ve seen is when someone’s storm drain emptied right next to the pool, and after a heavy rain, the dirty water slid right in. You can bet they had a metal staining problem.

Manganese 

Manganese stains a black-purple and brown-black-purple hue. While like the other metals, this could be found in well water—but it’s also present in municipal water, which is treated to reduce but not completely eradicate manganese.

how to remove metal stains from your pool

Put That Stain to The Real Test  

Again, that ascorbic acid test will certainly help you determine that it’s a metal, not organic matter, that’s leaving its mark on your pool. But an even better way to determine which metals are at work in your pool is to use good old water test strips. Make sure you get one that tests for metals like iron, copper, and manganese. If you really want to prevent this from happening again, it’ll help to know exactly which metal is to blame. Not that we’re pointing fingers or anything.

Send Those Metal Stains Packing—in Three Steps 

Did you confirm that you in fact have a metal stain making a home out of your pool? Well, get ready to use some muscle. Once you spend a little time prepping your pool, that stain will be coming off in no time. And of course, you’ll need to restore your pool’s chemical balance again once that’s done—but do it quick and you’ll be in the clear.

Restoring your chemical balance is all the easier with a powerful pump. If a larger horsepower will turn over your water volume at a sufficient rate—and won’t overwhelm your filtration system—then a unit like this Blue Torrent 2 HP Variable-Speed Pump is the one to try. As customer Dave Schmidt says, “My pool has never looked cleaner. I am pleased with my new pump!”

Step 1: Prep Your Pool 

You’re going to want your circulation system off for this. And while you might turn on your filter during Step 2, all other accessories—like chlorinators, metal ionizers, generators, and heat pumps—are better off not coming into contact with what you’re about to use to get rid of the stains. I promise, it’s not as scary as it sounds. 

Lower the chlorine level in your pool to between zero and two parts per million (ppm). You can wait for rainfall or drain part of your pool to achieve this concentration. This is significantly lower than the potency you’d want to properly sanitize your pool every day, but the lower the chlorine, the easier this next step will be. Because bad things tend to happen when your pool isn’t properly sanitized, add a dose of algaecide. This will prevent algae from taking over, which it can do—and fast. 

If this all seems like too much of a hassle for a couple metal stains, you can always get a metal stain remover, but read the instructions first—many will ask you to lower chlorine, anyway. 

how to remove metal stains from your pool

Step 2: Bye, Bye Stain 

I’m afraid our go-to sanitizer, chlorine, won’t cut it this time around. It has simply little to absolutely zero effect on metal. But hey—that’s a good thing. It allows pool accessories such as above-ground ladders to be made of ultra-sturdy steel. 

Since you know that this is a metal stain, you want to use ascorbic acid to remove the stain—much like you did for the test earlier, but now we’re getting serious. (If it was an organic stain, you’d want to use citric acid, instead.) Again, crushed up vitamin C tablets work, and you might already have them on hand. Now, rub ascorbic acid against the stain. After a few minutes, see if the stain is lightening. Continue to rub, wait, and check until the stain is gone.

For larger stains, add half a pound of ascorbic acid per 10,000 gallons of your pool water by sprinkling it evenly over the surface of the water. Then, turn your filter on to circulate. Allow it to run and the ascorbic acid for work for about half an hour. If the stains still aren’t gone, repeat this process of adding ascorbic acid, circulating, and checking until the stain is gone. 

Step 3: Now Back to Balance

It’s even easier from here on out. Now that you’ve got the stain gone, it’s time to get your chemical balance back to working order. The sooner you do this, the better—your levels are always easier to keep steady and maintain as part of your routine maintenance than fixing up all at once. It’s important to make sure your water is perfectly balanced before you take your next dive. With super low chlorine levels, I don’t even want to know what was putting up shop in your pool.

Once this is done, go ahead and turn on your circulation system again. Oh, and it definitely wouldn’t hurt to take this moment to shock your pool—though I won’t force it this time around.

I recommend tried and true shock like the Super Premium Sanitizing and Fast-Acting Pool Shock. Not only does it work fast in your water, but its conveniently packaged in one-pound bags, so you never have to worry about measuring yours out again. 

But How Did Metal Get There in the First Place?

Even if you’re most thorough, attentive, and overall consistent pool owner when it comes to maintenance, your pool can still end up with stains. But how? Well, it might be that your water comes from a well, or you have corroded metal somewhere in your greater water system. But metal can also come into your pool in surprising ways: the rain can wash metal substances into the water, small metal pieces such as screws can be dropped into the water, or you can simply use too much of a metallic algaecide.

The cause might be elusive, but that doesn’t mean you should shrug your shoulders and accept a metal-stained fate. I’ll show you easy measures you can take now to save yourself the hassle—and some significant elbow grease—in the future. 

how to remove metal stains from your pool

How to Prevent Metal Stains—In Five Steps 

These steps are all fairly low-maintenance. Do them all, and you’re on your way to a metal-free pool: 

1.     First, test your water source for metals. It’ll help to know exactly what you’re working with before you take any further action—you don’t want to be treating for iron when your problem is actually rusting copper.

2.     If you do find metal already in the water that you use to fill up your pool, add a filter to your hose to keep out excessive metals.

3.     Every week, add a dose of metal sequestrant to your pool. While this won’t remove metal from your pool, it’ll keep the particles from settling on pool surfaces. This way, they’re all the easier for your pool to filter out during its normal pump operation of about eight hours a day.

4.     Check in on your pool plumbing, and make sure there’s no rusting. If you have copper pipes, check them regularly for corrosion and replace any deteriorated pipes as soon as you spot them.

5.     This one is especially for copper stains. Maintain the pH level of your pool like you never have before. A low pH level means that your water is acidic, which corrodes copper and stains your pool.

Another option is a metal eliminator pack, which is designed to filter out metal over time and can be added to your skimmer basket or pump basket. It really couldn’t be easier.

The best pump to keep your pool—and your wallet—in top shape? The 1.5 HP Variable Speed Blue Torrent Thunder Pump tops the market in performance and is the most reasonable decision any pool owner can make: comes with a lifetime warranty, is eligible for rebates, and pays itself off in under one year.

how to remove metal stains from your pool

Iron to Never See You Again! 

The chemicals in your pool are back to their happy, normal levels and your pool walls and floor are stain-free—and you can go back to your regularly scheduled programming. And since you know easy ways to keep that metal out, you might never have to look up this particular blog post again. For now, the hard work is over, your pool is looking great, and if that’s not a reason to relax, I don’t know what is. Enjoy.

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