What to Do About Red Algae in Your Pool

Written by Michael Dean
March 27, 2024

treating pool algae

One of the worst things you have to deal with as a pool owner is all sorts of algae, bacteria, and other nasty things you don’t want to swim in. Red algae is one contaminant you may encounter during your tenure as a pool owner.

But what is red algae, and what does it look like? And if you’ve determined that you really do have a red algae problem, what do you do? Worry not; I’ve got you covered! Let’s dive in (after cleaning up the red algae, of course!).

Main Takeaways

  • Red algae is not actually algae but a type of bacteria that can be dangerous in a pool.
  • Poor pool chemistry, wind, rain, pool accessories, swimmers, and insufficient pool sanitization can all lead to red algae.
  • To get rid of red algae, you must clean every inch of the pool as well as shock it a couple of times.
  • To prevent red algae, clean your pool accessories, rinse before getting into the pool, and keep an eye on your pool chemistry.

Is Red Algae in a Pool Dangerous?

Naturally, the primary concern any pool owner might have would be whether red algae (also known as pink slime) is whether or not it is dangerous. The answer is simple: yes, red algae in a pool can be dangerous.

Interestingly enough, red algae is not really algae at all but rather a type of bacteria. If you leave the red algae in your pool without treating it, it can take over the whole pool, which can be dangerous (not to mention unsightly)!

Red algae release toxins that can cause skin irritation, redness, nausea, respiratory issues, vomiting, and dizziness.

Furthermore, keep in mind that red algae is slimy and can make the surface slippery, making a wet environment incredibly hazardous. Slips and falls around the pool can lead to a cracked skull or a concussion! So, as you can see, keeping an eye out for red algae infestations is important.

How to Identify Red Algae

Red algae is a pesky issue, so you should learn to spot it when it shows up. That way, you can immediately take the steps to treat it before it becomes a worse issue!

Luckily, it’s fairly easy to identify and can present in a varied range of shades, from rust-colored speckling, bright reddish-pink patches, or, most commonly, as a faintly reddish tint in the water. The texture will feel slick and slimy. Red algae can grow on any surface in your pool, including your pool walls, steps, floor, and even on pool equipment in the water.

What Causes Red Algae in a Pool?

So, how do you end up with red algae in the first place? Here are the causes of this nasty pink slime in your pool.

Poor Pool Chemistry

Most commonly, a lack of proper pool chemistry leads to red algae in a pool. If your pool water is not properly balanced with the right levels of sanitizer, pH, or CYA, this may lead to red algae!

Weather and Pool Accessories

This bacteria can also be introduced to your pool by external contaminated factors, such as wind, rain, and pool accessories.


Yes, humans can also cause red algae in a pool! In fact, humans are the main cause of red algae in a pool since we carry a wide range of bacteria with us when we go swimming, whether on our skin directly or on unwashed bathing suits.

Insufficient Pool Sanitization

Generally, when bacteria enter a clean pool that is sufficiently sanitized, the bacteria will die. But if you don’t shock your pool enough, the water in your pool is vulnerable to bacterial growth that is carried into the pool.

Step-by-Step Process: How to Get Rid of Red Algae in Your Pool

Once the red algae is in the swimming pool, the bacteria can spread throughout your entire pool, attaching to pool surfaces, such as the equipment, walls, and floors. The result is a slimy, gross, reddish-pink film that will flourish and harm swimmers if left unaddressed. You have to act quickly to take it down. Here’s my step-by-step process on how to do exactly that.

Step One: Remove Pool Accessories

Before you begin, remove all accessories from your pool, including pool toys, floats, and your pool ladder. Red algae can also stick to your pool accessories, so scrub them all thoroughly with a bleach solution made of half bleach and half water. Use a soft brush to scrub and clean the accessories. Don’t forget to wear proper protective gear when doing this!

Step Two: Clean the Filter

Now, to clean the dirty water of this pink slime, you will have to clean your filter. If you have a sand or DE filter, backwash it. If you have a cartridge filter, either replace the cartridges if it’s time or remove the cartridges and clean them thoroughly.

Step Three: Test and Balance the Water

Test your water chemistry. Make sure everything is balanced as it should be. If anything is out of range, balance the water to fit within the recommended range of water chemistry levels.

Step Four: Brush the Pool

Now for some elbow grease! Grab a pool brush and pole. Then, begin brushing the walls of the pool with the pool from wall to floor, from the shallow to the deep end. Brush thoroughly, and apply a firm pressure to dislodge the red algae from surfaces. Remember: red algae can really cling onto surfaces, so brush well!

Step Five: Skim and Vacuum the Pool

Once you’ve brushed the entire pool, skim out any dislodged grime that might be floating on the surface. To make it easier, you could use pool floc to bundle up floating particles into easy-to-scoop clumps that will be caught in your net.

Follow this up with a vacuum for good measure

Step Six: Shock the Pool

Once you’ve done this, it’s time for a round of pool shock. The idea is to raise the sanitizer level to double or triple the usual amount to thoroughly kill any lingering bacteria. Measure the dosage out, mix it in a bucket of water, and then walk around the perimeter of the pool, pouring the shock in slowly.

Step Nine: Filter the Pool

After you’ve added the pool shock, it’s time to run the filter to allow for even circulation and sanitization of the water. The key here is to keep the filter running until you’ve eliminated all the red algae! So, yes, in some cases, this means leaving the filter running 24/7.

Step Ten: Do It All Again!

Once the chlorine levels drop back down to around 2 to 4 ppm, do it all again! First, clean and backwash your filter to get rid of all the pink slime in the filtration system. Then, brush the entire pool again! Follow that up with another dose of pool shock for good measure.

Step Eleven: Rebalance the Pool

When the chlorine levels are back to normal once again, and there is no more red algae in your swimming pool, rebalance the pool and ensure everything is within the proper ranges.

And that’s it! However, if the infestation is severe and you cannot handle it, I always suggest calling a professional for help.

How to Prevent Red Algae

It’s a lot better to prevent the pool from getting red algae in the first place, and you’re in luck! Here are my best tips and tricks for red algae prevention. These tips will also come in handy in keeping your pool clean and healthy in general!

  • Clean your pool cover twice a year.
  • Always balance and keep an eye on your pool chemistry, particularly your sanitizer, pH, alkalinity, and CYA levels.
  • Run your pump and filter for at least 8 to 12 hours every day.
  • Regularly clean your pool by brushing, vacuuming, and skimming.
  • Clean your pool accessories often, including the pool ladder, pool toys, and floats.
  • Keep your bathing suit clean.
  • Have swimmers take a quick shower or rinse before jumping into the water.

Get My Free Pool Care Checklist

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Red Algae: Bad News for Your Pool

Whatever the case, red algae is bad news for your pool. Treating the issue promptly as soon as it appears is the way to go. If you overlook it or ignore treating the problem right away, you might find yourself besieged by a severe red algae infestation in a mere matter of days, and that is an exhausting fight.

I hope this guide helped clarify things! If you have any questions about battling red algae or other contaminants in your pool, please don’t hesitate to message me. I’m happy to help! Check out my main swimming pool maintenance hub for more tips on keeping your pool clean.

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