How to Remove Algae from a Salt Water Pool

Written by Michael Dean
September 21, 2023

algae in a salt water pool

It’s a common misconception that saltwater pools are safe from some of the problems that plague regular chlorine pools. While it’s true that saltwater pools offer several benefits that chlorinated pools don’t, a saltwater swimming pool can also turn green or have an algae infestation, much like a regular pool. But how do you fix a green saltwater pool? You’ll need to fix it before you can safely use your pool again.

In this article, I will explain why a saltwater pool turns green, how to sort it out, and how to prevent algae from sneaking back into your swimming pool again.

Main Takeaways

  • Saltwater pools can turn green because of rainy weather, dysfunctional filtration, poor circulation, low chlorine levels, or nutrient-dense water.
  • Types of algae that can invade a saltwater pool includes green algae, yellow algae, black algae, and pink slime.
  • Clearing a green saltwater pool involves adjusting chemicals, cleaning the pool pump and filter, shocking the pool, and brushing and vacuuming the debris.
  • To prevent algae from creeping into your water again, test your water regularly, brush your pool walls, use a pool cover, and maintain proper chemistry levels.

Why is My Saltwater Pool Green?

The common culprit behind a green saltwater pool is almost always algae. There are many ways for algae to creep into your pristine water. Spores can be deposited into your pool via rain, wind, dirty swimsuits, and organic waste. Then, conditions such as low chlorine levels, sunlight, warmth, and stagnant water can create the perfect environment for those spores to multiply and expand into a full-scale algae bloom infestation.

Ordinarily, your best bet to avoid a pool full of algae spores multiplying every second is to keep your pool healthy and your water chemistry balanced. If you remove the conditions necessary for algae spores to flourish, it’s unlikely you’ll encounter green water overnight.

That said, life creeps up on us, and we may occasionally miss a day or two of pool chores. Or sometimes, even the most perfectly balanced swimming pool can turn green due to a heavy rainstorm, for example. Whatever the reason for your green saltwater pool, you will need to fix it before enjoying your pool again.

The Role Your Salt Chlorine Generator Plays in Algae Prevention

A salt chlorine generator is your friend in the fight against algae contamination. It converts the salt you add to your pool into chlorine via an electric current that zaps the pool water as it passes through the machine. By comparison, in a standard pool, chlorine is added directly to the pool water.

Regardless of pool type, once the chlorine hits the pool water, it is converted to hypochlorous acid, which is the stuff that fights the algae, bacteria, germs, and other unwanted aquatic invaders.

In a saltwater pool, chlorine is released at a slower rate than in a chlorinated pool, which means that the chances of algae taking root are much higher. To make sure that your pool stays balanced, test your pool water at least several times a week. There is no such thing as over-testing, though, so if you want to check more frequently, you can!

When you test and balance your saltwater pool, you need to make sure that the amount of hypochlorous acid – the stuff that kills algae – is just right; otherwise, your pool water will be too acidic or not acidic enough. You need to be sure that the other chemicals in your pool are also properly balanced.

The salt chlorine generator makes it easier to balance your pool water and will warn you if your salt levels are out of range. However, make sure that you know the right balance of chemicals for your pool water. I’ll cover those ideal chemical levels in my step-by-step guide below.

Types of Algae That Can Invade a Salt Water Pool

There is a myriad of ways that algae spores can enter your pool, including:

  • On your bathing suit, pool toys, pool cleaning tools, etc.
  • Wind can blow spores into your pool.
  • Heavy rains can wash spores into your pool.
  • Direct sunlight can break down chlorine faster, leading to algae overgrowth.
  • High temperatures can accelerate the growth of algae once it is in your pool.

Several different types of algae can set up shop in your pool. The type of algae will determine how difficult it will be to remove.

Green Algae

Green algae are the most commonly seen algae in pools and grow very quickly. If you’ve experienced your pool changing colors seemingly overnight, it was likely due to green algae contamination. Green algae also generate energy and feed off of sunlight. That is why algae contamination can get out of hand quickly on sunny days.

Green algae usually look slimy and tend to cling to surfaces. Here’s a photo of what it looks like in a very dirty salt water pool.

The good news is that while green algae may take over rapidly, it is the easiest to remove. To clear your green pool, you will probably need to shock your pool twice. Check out my guide on how to shock your pool if you don’t know the proper steps.

Yellow Algae

Yellow algae, or mustard algae, usually grow slower than green algae. Unlike green algae, it grows best in shady spots and still water. It typically looks dry or powdery, so initially, you may mistake it for dirt, pollen, or sand on the bottom or sides of your pool.

Yellow algae contamination can also resemble a stain or a blob at the beginning. So, overall, not a good look for your pool.

Yellow algae are resistant to chlorine, so it is also more difficult to remove than green algae. You may have to shock your pool three times to get your yellow algae contamination under control fully.

Black Algae

Black algae look like mold and may start as a few black spots that eventually can grow into clumps. Black algae tend to grow more readily on porous surfaces, so it is less likely to contaminate fiberglass or vinyl-lined pools. Black algae can make you sick, so do not swim in a pool that appears to be contaminated.

Black algae are more resistant to chlorine than green or yellow algae and are the hardest to eliminate. You may have to quadruple shock your pool water to put an end to the contamination.

Pink Slime

Pink slime is actually a bacteria, though sometimes people refer to it as algae. Like algae, pink slime is another commonly occurring problem in pools. Pink slime may look like sludgy or mucousy streaks. It is not sanitary, and you should avoid the pool until the contamination is under control.

Pink slime is just as stubborn as black algae. You may need to shock your pool three or four times to fully remove the bacteria.

Step-By-Step Process for Removing Algae From Your Salt Water Pool

Ensure that you have all of the tools you will need to clean up your saltwater pool on hand before you start. You will need the following:

Here are the steps to remove algae from a salt water pool:

  1. Test and rebalance your pool
  2. Check your salt chlorine generator
  3. Shock your pool
  4. Brush the pool
  5. Vacuum and clean your filter
  6. Test again

Let’s cover each of these steps in more depth.

Step One: Test and Rebalance

The first thing you have to do is grab your saltwater pool testing kit. You’ll need to test for salt, chlorine, pH, total alkalinity, and cyanuric acid levels. Rebalance any pool chemicals if they’re out of the recommended range. To refresh your memory, saltwater pools are best at the following levels:

Total Alkalinity: 80 – 100 ppm
Cyanuric Acid: 60 – 80 ppm
Free Chlorine: 1 – 3 ppm
Salinity: 3000 – 4000 ppm
pH: 7.2 – 7.8

Step Two: Check Your Salt Chlorine Generator

You need to ensure your salt chlorine generator (SWG) is functioning properly at the correct production rate. For instance, if your salt is within range, but your chlorine levels are lower, the generator may not be making enough chlorine, which you’d have to increase. If both chlorine and salt levels are low, more salt must be added, and so on.

Step Three: Shock Your Pool

Once your chemicals are in line and the SWG is functioning as needed, shock your pool. Depending on the type of algae you are dealing with, you may need to double-shock, triple-shock, or quadruple-shock your pool.

A double shock may suffice if you’re just dealing with some common green algae. But if you are dealing with dark green algae or mustard algae, you should triple-shock. And finally, if you have the dreaded black algae in your pool, you’ll need to quadruple-shock the saltwater pool.

To shock the pool, measure the amount needed as per manufacturer guidelines and the size of your pool, then double/triple/quadruple it and pour it into your pool slowly while walking around the perimeter. Do this at dusk or night, and turn your pump on immediately for the next 24 hours to properly circulate the chemicals.

Here’s my favorite shock to use for cleaning up saltwater pools.

In The Swim Calcium Hypochlorite Chlorine Granular Pool Shock

In The Swim has a reliable cal hypo shock that is effective and easy to use.

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I may earn a commission if you make a purchase, at zero additional cost to you. This in no way impacts my research process or opinions.

Step Four: Brush the Pool

Now, it’s time to grab a brush and brush down every inch of your pool’s surface. Algae spores cling to your pool tiles, making them harder to get rid of than your standard debris. By brushing, you dislodge the algae and expose it to the shock and chemicals present in your pool. Brush evenly, in a downward stroke, starting from the shallow end to the deeper end of the pool. Make sure to cover all surfaces, including the steps and the perimeter.

Step Five: Vacuum and Clean Your Filter

After brushing, vacuum up the algae and debris. If the particles are too fine to filter, use a clarifier or a flocculant to clump them together, making it easier to fish out with your vacuum, skimmer net, or pump. In addition, backwashing your filter after clearing a green pool is a great idea—your filter may be clogged after clearing up a heavy load of dead algae.

Step Six: Test Again

Once you’ve completed the above steps, test your pool once more to check if all chemicals are balanced. Your pool should be crystal clear, blue, and safe for swimming again. If it isn’t clear after a few days, you might need to consult a professional to troubleshoot the exact cause of the problem and try again.

How to Prevent Algae from Returning in Your Salt Water Pool

Preventing algae in your saltwater pool can be challenging, but with the proper steps and regular maintenance, it is possible to keep your pool clean and sparkling.

Proper Filtration

Pool owners often incorrectly assume a saltwater pool needs less filtration and maintenance. Saltwater pool filters also need maintenance and cleaning for the chlorine to be effective. Circulation is also vital since algae love warm, moist, and stagnant environments. An efficient pump and filter system goes a long way in keeping the water clear and free of contaminants. The filtration system should also be appropriately sized for your pool to ensure it can handle the volume of water and remove debris effectively. Read my article on saltwater pool maintenance for all of my tips on keeping this type of pool clean.

Reduce Nutrient Sources

Algae feeds on nutrients such as nitrogen and phosphorus. To prevent algae growth, limit the amount of these nutrients entering your pool by avoiding the use of fertilizers near the pool, preventing food or drinks from spilling into your pool, disinfecting/showering before you (or other guests) enter the pool, and using a pool cover to protect spores or debris from entering the water via a strong wind or a rainstorm.

Maintain Proper Water Chemistry

As always, one of the best things you can do to prevent a saltwater pool from turning green is to consistently maintain the correct levels of chlorine, salinity, CYA, alkalinity, and other chemicals used to treat the water. Test your water once a week and rebalance any errant levels, especially during the summer when the chlorine demand is high. This is vital to keep the water clear and prevent algae from taking root.

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Frequently Asked Questions

Can I use the super chlorination mode on my SWG to fix green pool water?

Well, not exactly. Chances are the first solution you’ve thought of when dealing with a green saltwater pool involves flipping the switch on that “super chlorinate” feature on your chlorinator. But in reality, it’s slow to work and doesn’t deliver nearly enough chlorine to destroy algae spores. It’s a useful feature to have after high bather loads (a pool party) or mild bad weather, but if algae spores are already in the water, it will not fix a green pool. The best way to fix a green pool is to shock it.

How long does it take for a green saltwater pool to clear up?

At best, it could take up to one or two days to completely clear a small amount of algae. However, if you’ve experienced heavy contamination, it could take a week to clear up. In any case, I recommend holding off swimming until it’s completely cleared up.

Final Thoughts

With these few observations and methods, you’ll have a clean, algae-free pool in fewer than ten easy-to-follow steps. Removing algae from your saltwater pool is as easy as preventative maintenance. Avoiding an algae infestation is even easier. Once you know why algae grow in pools and what to do to prevent it, you should not have to fight another full-blown contamination again.

Your pool is ready to be enjoyed once you have completely cleared the algae and your pool water balance is restored. Though most algae are not harmful, try to avoid swimming in pools with algae or slime build-up, as some types can make you sick.

As always, let me know if you have any questions. Head to my article on saltwater pools 101 for more advice on this type of pool. I also wrote a guide on how to clear a green pool if your friends and neighbors have a traditional chlorine pool.

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