Pool Algae Treatment

Pool algae is a living organism that can bloom and multiply turning an entire pool green and nasty in as little as twenty-four hours. Algae spores can get into any pool through rain, wind, leaves or from swimmers that were previously in contaminated water.  If you currently have a green and ugly mess caused by algae instead of a sparkling blue swimming pool we can help you get it back to normal by following our how to kill algae guide below so you can start enjoying your pool again.

pool algae

If you have ever experienced green pool water before you will know how frustrating it can be to get your pool back to normal. The good news is that we are going to explain how to eliminate algae and get your pool looking crystal clear as well as some preventative tips for owners that have algae that keeps coming back.

If you are a salt water pool owner the likelihood of experiencing pool algae is significantly lower because salt is a natural deterrent but if you do experience algae blooms it will be easier to remedy than if you had a regular swimming pool. 

Algae can form for a number of different reasons and the frustration can be compounded when the algae keeps coming back. Most pool owners will never experience blooms while others have to deal with the problem repeatedly and if you find that you are constantly battling algae we'll help you get rid of it once and for all. We will start out by explaining the different types of algae followed by steps you can take to treat and prevent break outs in the future. 

salt water pool maintenance guide

Types of Pool Algae

If you have algae in your pool right now the first step is to identify what kind you are dealing with so you can get rid of it effectively. The remedies vary so it is important to spend some time to learn about the different types of pool algae and after you have a good idea of the culprit you can work through the steps below that explain how to get deal with each kind. 

Green Pool Algae

This is the most common type but on the bright side it's also the easiest to kill. It can be found floating freely in your pool creating very distinct green pool water. It can also be found growing on pool walls, on the bottom of your pool or in crevices. It can drastically reduce water clarity and will often form during periods of inadequate circulation and poor water chemistry. 

Yellow Pool Algae or Mustard Algae

Yellow colored spores are often referred to as mustard algae simply because of the color.  It is often mistaken as yellow stains and can be confusing because it looks like sand or dirt lying on the bottom of the pool. If you have this organism living in your pool you will be in for a bit of a battle but the good news is there are some great products designed specifically to kill it as well as prevent it in the future.  

Black Pool Algae

The hardest to get rid of is black algae because of it's deep roots and ability to defend itself against sanitizers. It is very uncommon but when it does form it will likely be found on the walls and in corners of plaster pools growing in small black patches. If you have tile you may find it growing along the grout lines where it can sink its roots and take hold.  

Pink Pool Algae

Pink algae can appear in small areas either in crevices or corners behind pool hardware where circulation is limited. It is a slimy pinkish-red substance that is actually a bacteria and looks like rust on your pool walls. It is different than black algae in that it likes to form on smooth surfaces where brushing is infrequent. 

How to Kill Pool Algae 

After you have determined which type of algae you have in your pool it's time to put together a plan to eliminate and prevent it from coming back. The methods for getting rid of the different types of algae are roughly the same it's just a matter or using a higher concentration depending on how severe the outbreak appears. The following steps will explain how to get rid of green algae and mustard algae because they are by far the most common.  

1.  Water Chemistry

The fact that you have algae in your pool is most likely due to poor water chemistry and should be the first thing you address. If you don't have a good quality pool water test kit you will need one to get accurate readings so you know what to adjust. If you don't feel comfortable testing on your own you can take a water sample to a local pool dealer. 

The pH level between 7.2 and 7.6 is the most important because it will allow the chlorine to work most effectively within this range. Keep in mind that a high pH level may have been a contributing factor to your initial algae outbreak. You will also want to make sure that your other levels are within recommended range including alkalinity and sanitizer and if you want more detailed information you can check our page on pool maintenance

Properly balanced pool water will increase the effectiveness of the shocking process. 

2.  Brush

A thorough brushing is important because it will loosen up and disturb algae that has made its home in your pool, making it easier to kill. It will be the most labour intensive part but worth every minute because you want to make sure that the algae never comes back. You should pay special attention to areas behind steps, ladders and hidden crevices where it likes to hide.

If you have a vinyl liner you should use a nylon brush and for concrete you should use a steel brush. You may also want to use a pumice stone to get the really stubborn algae especially if you are dealing with black algae in a concrete pool. If you would like more related information on cleaning be sure to read about pool tile cleaner

With mustard algae and black algae it's very important to brush vigorously and removed as much of the spores as possible. 

3.  Shock or Superchlorination

A shock is designed to kill bacteria and pool algae by raising chlorine levels up temporarily and if you are a salt water pool owner you may be familiar with super chlorinate if your chlorine generator has this feature. The amount of shock you need is determined by the color and type of algae you have in your pool:

Light Green Algae - 2 lbs of shock for every 10,000 gallons of pool water
Medium Green Algae - 4 lbs of shock for every 10,000 gallons of pool water
Dark Green Algae - 6 lbs of shock for every 10,000 gallons of pool water
Black Algae - 8 lbs of shock for every 10,000 gallons of pool water
Yellow Algae - Yellow Out or Yellow Treat

The most common shock contains calcium hypochlorite but you may find that shock containing lithium hypochlorite, di-chlor (cyanuric acid) and potassium peroxymonosulfate are better for your pool. They all get the job done but as a pool owner you should know the differences and how they will affect the chemistry of your pool in the long run. Learn more about how to shock a swimming pool

Flocculant or Floc

A flocculant is a coagulant that clumps pool algae and other materials into larger groups making it possible to vacuum them from your pool. The clumped algae will collect at the bottom of the pool and needs to be vacuumed out manually to get it out of the pool. This method is a lot of work but it's a fast way to get algae out and your pool looking better. A floc should always be followed up by ensuring chlorine and pH levels are safe.

Algaecide or Algicide

Some algaecides will kill pool algae and some won't so be sure to check the label before purchasing. They are best used as a preventative measure to kill algae before it blooms and becomes harder to eliminate or in tandem with a shock or floc.  ou should use quaternary ammonia algaecides called poly-quats just make sure that they don't have foaming agents or metal-based ingredients that can cause staining.  

4.  Test Water

After the appropriate shock or combination of shock, floc and algaecide you want to test your water again after it's had a chance to circulate for 24 hours. If the shock was successful you may notice white or grey dead algae suspended which can cause cloudy water. Either way you want to test for chlorine and pH levels to see what is going on in your pool.

  • If your chlorine levels are elevated and the algae is still alive you should maintain these levels for the next couple days by adding more shock if necessary.
  • If chlorine levels are not significantly higher you may need to shock a second time to elevate levels. If you still see no change in chlorine levels you may need to shock several times or partially drain your pool.

5.  Vacuum and Clean Filter

If you notice that algae is still visible after a couple days you may need to brush more vigorously and give your pool a good pool vacuum. If you are maintaining good pool chemistry and you brought chlorine levels high enough with a good shock you should start to see a noticeable difference by day three at the latest.  

Once you see that there are no more signs of pool algae it's time to give your pool a very thorough vacuum with a manual vacuum cleaner. This will ensure that you get all the dead algae out of the pool that may have collected at the bottom. You can let your pools circulation and filter deal with the dead algae but this can cause clogging and may take several days to clear up your pool.  

The final step to eradicating pool algae is to give your filter a good clean or backwash. The last thing you want is the algae to take over your pool again so you want to clean your filter with muriatic acid. Cleaning the filter will clear the dead algae out that may block filtration and will also help prevent algae from spreading again. 

How To Prevent Algae Growth

If you spent time, money and possibly some sweat and tears getting your pool free from algae you will probably be motivated to prevent pool algae from growing in your pool again. Just like everything else it's definitely worth putting in a bit of preventive effort in now to avoid bigger headaches down the road. 

Every pool is different and you should be aware of the factors that could possibly put you at a higher risk of developing algae:

  • Poor water quality including improper levels of sanitizer (chlorine), pH and alkalinity.
  • Poor circulation caused by inadequate run times, ineffective filter, underpowered pump or clogged plumbing and jets.
  • Poor maintenance routine including brushing and vacuuming.
  • Hot and sunny weather over an extended period.

It goes without saying that water quality is the most important thing when it comes to maintaining a healthy pool. If you stay on top of chemistry in your pool water you should never have an algae problem. If you are someone that likes added peace of mind you might consider using an algaecide every week that isn't metal based or cause foaming. 

If you suspect that circulation is the issue you should start with assessing the performance of your pump. A pump should turn over the water in your pool twice every day to ensure adequate filtration and in the case of a chlorine generator it's even more important. Plumbing and jets should all be inspected to ensure that there are no dead spots in your pool that leave areas of stagnant water. 

Pool algae likes water that is still and undisturbed and that is why giving your pool a weekly vacuum or brush is such a good deterrent. It can be an automatic or manual vacuum or simply a brush but it's worth taking 10 - 15 minutes a week.

While there is no ideal growth temperature for algae it will flourish if conditions are suitable and your pool water is between 60 - 80F (16 - 27C). Hot weather and plenty of sunshine can also cause pool algae spores to multiply through the process of photosynthesis.  


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