Going… going… green. Whether you noticed your water start to slowly darken or you suddenly discovered a swampy pond where your pool used to be, a green saltwater pool can be pretty confusing. Isn’t the concept behind a saltwater pool that it operates at the lowest, most stable chlorine levels possible? What’s stable about green water, then?
Unfortunately, even saltwater pools have their limits. But if yours is experiencing some seriously green water, there’s no guesswork to do. That’s the silvery green lining: green water comes from one cause and one cause only.
I’ll explain why your saltwater pool is green, how to identify the actual invader, break down why you need to act fast if you have green water, and describe a straightforward method for getting that water back in the clear. The sooner you eradicate the problem, the better—so let’s go.
Quick Refresh: Here’s How Saltwater Pools Work
Saltwater pools don’t technically sanitize with salt (at least, it doesn’t end up as salt). I know, the name makes it a little more confusing. But actually, saltwater pools use good old chlorine just like traditional pools—except they generate chlorine on-site, and keep the levels so low that you hardly know they’re there. That means that even though your pool is sanitized, you won’t have your hair turning colors, your skin burning, or your floaties and swimsuits getting slowly eaten away. Believe it or not, exposure to high concentrations of chlorine can make that happen.
Here’s how a saltwater pool works. The salt cell, or generator, draws in the dissolved salt in your water, and then converts it to chlorine using a process called electrolysis. Through this process, it is able to circumvent oxidation, which is what usually produces common chlorine byproducts called chloramines. It’s not technically chlorine that wreaks havoc on swimmers. It’s chloramines, their noxious, uncomfortable spawns. Without those, it’s as if you’re shocking your pool every single day—without the work.
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Why Is Your Saltwater Pool Green? There’s One Culprit
The good thing here is that if your saltwater pool is green, you don’t have to diagnose the problem—at least, not initially. Green water has one culprit, and that’s algae.
Algae can be introduced into any pool, no matter what sanitizer it uses. That’s because no sanitizer type is fully equipped to prevent or attack algae all on its own. Whether you have a chlorinated pool, a saltwater pool, or a biguanide pool, an algae infestation is always a possibility, and you’re always going to want a backstock of pool shock just in case it happens to you.
Although it’s always a good idea to thoroughly wash any swimsuits, pool toys, or equipment that has come in contact with algae to prevent a reintroduction into your pool, this green giant can also simply enter your pool through spores in the rain. In other words, it can happen to anyone, even with a perfectly chemically balanced pool.
But just because it can happen to anyone doesn’t mean the chances of an infestation are equal across the board. Algae is especially likely in pools that lack chemical balance, as well as pool water that tends to be kept at higher temperatures. This green plant loves warmth—and hey, I’m right there with them.
Why Is Algae a Problem?
An algae infestation is a sure sign that your chemical balance is out of whack. Unfortunately, all forms of algae are known to exhaust your sanitizer. And once that happens, your pool water is no longer safe for swimming. Remember, sanitizer’s job is to neutralize all the bad bacteria in your pool, including the pathogenic kind that could potentially make you sick. And if that microscopic bacteria is allowed to run amok, the rest of your chemicals are going to be harmed in the process.
Plus, algae usually has room for infestation when your pool doesn’t have a lot of free chlorine—in other words, if you’re skipping your weekly dose of pool shock. And if you’re not shocking every week and your free chlorine is low, your sanitizer actually doesn’t have the bandwidth to do its job. That algae is signalling that there could have been harmful bacteria in your pool—before you noticed the bloom.
Since this is an issue of swimmer safety, it’s important to get out algae as soon as you see it. My advice is to put a massive pause swimming in your pool until you can be sure it’s gone.
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What Kind of Algae Is Yours?
Now that you know that your green water is being caused by algae, it’s time to identify what type of algae is coming up. Green would be the obvious answer, but sometimes these other types can be tricky to nail down, because they also make the water look cloudy, greenish, or some other strange hue.
Green Algae
Green algae is your standard algae, and probably looks most like what you imagine when you think of algae. It’s similar in color to other green vegetation, manifests in blooms under and on top of the water or in moss-like patties floating on the pool’s surface, and multiplies fast.
Mustard Algae
Mustard algae is also called yellow algae, and it can be mistaken for debris such as dirt and sand. It usually gathers at the corners or bottom of your pool floors. In order to tell whether or not you’re seeing mustard algae or a pile of sand, use an antimicrobial pool brush to give it a nudge. If it disperses immediately, you’ve got yellow algae on your hands.
If this is your situation, well, that’s not a good thing. Mustard algae can actually survive outside of pool water, including on swimsuits, pool toys, pool equipment, and more. Eradicating yellow algae from your pool includes sanitizing anything that has come into contact with your water, which can be a lot of work.
Black Algae
Black algae doesn’t look like your typical swamp-green bloom. Instead, it manifests as black spots along the surfaces of your pool—especially those that are less smooth and have more rugged surface area for this algae type to cling on to. Black algae can actually dig roots into the surface of your pool walls and floors, so it can be especially tough to eradicate.
Sorry, No Shortcuts!
If my hunch is right, you’re eyeing that superchlorinator setting on your saltwater generator right about now. That’s a tool that most generators come with, and it allows you to boost chlorine output all the way to 100% for a full 24 hours. It’s a lot, I know. And yet, when it comes to algae, it’s just not enough.
This mode is intended for when you’ve had a significant amount of swimmers sharing the pool, such as after a pool party or if you’ve hosted local swimming classes. As part of your chemical balancing for a saltwater pool, you should also set your chlorinator to this mode once a week, similar to how you want to shock your pool every week.
Unfortunately, it’s not intended for algae. You’ll need some elbow grease to take care of this problem.
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How to Fix a Green Saltwater Pool—In 5 Steps
Like I said, no shortcuts for this one. To eradicate algae from your pool, you’re going to need some physical strength. That being said, it’s better to take a rest when you need one than skip a step. This will only work if you do it the right way—especially if you’re dealing with some yellow or black algae.
1. Brush the Bad Guys Away
First, you have to uproot that algae before you can make sure it’s gone for good. Scrub your pool floors and walls using a antimicrobial brush like the 360-Degree Bristles Pool Brush, which was developed by pool maintenance experts to help get tight corners without any of the aches or pains associated with a good clean. It’s also treated with hospital-grade antimicrobial finish, which will prevent that algae from living it up on your brush while they wait to enter the pool again.
2. Vacuum!
Once you’ve scrubbed your walls, floors, and steps clean (and behind any ladders, if you’ve got them!), remove large debris like leaves and twigs with a skimmer net on a telescopic pole, and then manually vacuum out all the algae to waste. You don’t want any algae to circulate back out, or you’ll be here again before you know it.
3. Put Your Water to the Test
Again, algae sucks up your sanitizer and other chemicals, so if you’re dealing with an infestation you can be sure the water is far from balanced. Now’s the time to get your levels right, so that the pool shock you’re about to use has the space to do its job. Two chemicals you’ll need to pay special attention to are pH and alkalinity—if you have a high pH or a low alkalinity, it’ll prevent this next step from working. Use water test strips to make sure your balance is up to snuff, and adjust as needed.
4. Shock… Wisely
Now it’s time to really get things moving along—and send all that algae packing. It’s time to add pool shock to your water. We’re about to double, triple, or even quadruple shock that pool. For saltwater pools, make sure to use calcium hypochlorite shock.
For green algae, double the average dose. For yellow algae, you’ll need three times as much. And for black algae, you’ll need four. Extreme circumstances call for extreme measures. Be sure to follow your manufacturer’s instructions and measure out the amount of shock you need based on how many gallons your water contains. Once you know how much you’re adding, it’s usually as easy as slowing walking around the perimeter of your pool and dropping the shock right in. Make sure that your pump is turned on immediately so all those chemicals circulate and are eventually evenly distributed across your water.
Just remember, as always, to shock your pool at dusk or night. You don’t want the sun burning down your pool shock’s ability to work when you need it the most. Also, don’t swim for at least eight hours—certainly not while your pool is still cloudy with shock.
5. Test Again
Algae can seriously mess up your chemicals, even for the short amount of time it was in your pool before the shock did its job. Go ahead and get out your test strips one more time, and make sure everything is in order.
If your levels are looking on the mark, and your water is no longer cloudy with shock but back to sparkling clean, congratulations—you’re done!
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How to Prevent Algae in Your Saltwater Pool
Don’t want to have to do that ever again? I don’t blame you. The good news is that you can significantly reduce your chances of an algae infestation with a few simple measures.
As soon as you finish getting algae out of your pool, you should always backwash your sand or diatomaceous earth (DE) filter, or give your cartridge filter a chemical wash. Chances are there are algae spores in your filter just waiting to go back into your water, so it’s time to make sure they’re gone. If you’re due to replace your sand, DE cells, or cartridge media, now is a good time.
Moving forward, it’s important to wash your swimsuits, pool toys, and other equipment regularly, especially if they’ve come into contact with a natural body of water or algae in your pool.
The last tip I have to prevent algae is also one of the most foundational: don’t sleep on your chemical balance! Testing your water weekly as well as using your superchlorinator boost is essential to a healthy chemical ecosystem in your pool. Remember, the more free chlorine your pool has, the lower the chance of these green guys making a comeback.
Green Be Gone!
It wasn’t exactly easy, but you got that algae out of your saltwater pool. This accomplishment leaves all the more time and energy to enjoy your clean, sparkling, ultra-comfortable water. And thanks to the benefits of having a saltwater pool, even if your pool sometimes turns green, your hair just won’t. See you at the pool.
