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How to Identify and Kill Black Algae in Pool

How to Identify and Kill Black Algae in Pool
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Most of the pool issues that pool owners deal with are really not a big deal. You will have to play with chlorine levels or do a little extra scrubbing, and things will be back to normal. However, when it comes to black algae, things are a bit different. This is one of the more annoying pool issues to have, and it will likely end up costing you quite a bit of time and money to deal with. Luckily we have all the information that you need to get rid of black algae and keep it away for good.

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Clorox Pool&Spa Active99 3” Chlorinating Tablets 5 lb.
In The Swim Chlorine Pool Shock - 6 X 1 Pound Bags
In The Swim Super Pool Algaecide - 1 Quart
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Clorox Pool&Spa Active99 3” Chlorinating Tablets 5 lb.
In The Swim Chlorine Pool Shock - 6 X 1 Pound Bags
In The Swim Super Pool Algaecide - 1 Quart
$63.95
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#1
Clorox Pool&Spa Active99 3” Chlorinating Tablets 5 lb.
4,003 Reviews
Clorox Pool&Spa Active99 3” Chlorinating Tablets 5 lb.
$63.95
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#2
In The Swim Chlorine Pool Shock - 6 X 1 Pound Bags
1,984 Reviews
In The Swim Chlorine Pool Shock - 6 X 1 Pound Bags
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In The Swim Super Pool Algaecide - 1 Quart
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In The Swim Super Pool Algaecide - 1 Quart
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What Is Black Algae?

There are usually three types of algae that you will encounter in your pool. The green algae, mustard algae, and black algae. Black algae is a single-celled organism that grows in a large colony. Black algae contain certain compounds that keep them from showing the prominent green color that we see in green algae.

Black algae in pool water are more difficult to remove than both green algae and mustard algae. The black algae have become fairly resistant to the chlorine treatments, and that is what makes it a bit harder to remove black algae in your pool.

Why Do You Have Black Algae in Pool?

Of course, we need to get started on fixing the black algae problem that you have in your swimming pool. However, first, it is a good idea to think about how this could have happened. You will want to make sure that you do everything possible in the future to prevent black algae.

Black algae most commonly come from bathing suits that were worn in a different pool, the ocean or a lake. The black algae are carried in on the material, and then it is left to breed in your pool.

You may also get black algae from airborne spores. This is a bit less common and could be harder to prevent.

What Does Black Algae Look Like?

One of the reasons swimming pool owners struggle with the black algae issue is that they can’t identify the problem. Black algae can at first look like a bit of dirt growing in the corner of your swimming pool. Pool owners may try to use pool shock and a good vacuum of the pool, but they notice these spots don’t go away.

Here are a few key things to remember when you are trying to identify black algae.

  • Black algae will not be floating in your pool water
  • Black algae attach to a hard surface and dig in quite deeply
  • Sometimes, the color can be a bit blue/green, and it will be raised from the surface of your pool
  • When you try and brush off the black algae, it will not brush easily

Is Black Algae Dangerous for Your Pool?

Black algae are dangerous for your pool and for the users of the pool. People should not swim in a pool that has a black algae problem. Although just being in the swimming pool water may not cause any issues, swallowing the water can become a serious problem.

Most kids and even adults that swim will end up ingesting a bit of the pool water. With normal clean pools, this is not going to be an issue. However, if there are black algae in the pool, the bacteria can be ingested and cause serious issues. Algae spores are a bit dangerous, and until you get the black algae out of your pool and all of the pool toys, pool walls, and pool surfaces back to normal, it is a good idea to shut down the pool.

How to Kill Black Algae Fast (10 Steps)

Now the part you have all been waiting for, how to kill black algae fast. Your idea of fast and our’s maybe a bit different. For most people, you will probably spend about a week taking care of this black algae problem. You may have luck after about five days or so, but this will be a process that requires some of your attention every day. If someone tells you that you can remove black algae from your pool in 24 hours, you have likely not completely treated and dealt with the issue. Here are our steps for removing black algae and keeping it away for good.

Step 1: Gather Your Materials

To complete this process, you are going to need to grab a few supplies. Having everything you will need ahead of time will make getting rid of black algae a bit easier.

  • Pool scrub brush
  • Chlorine tablets
  • Stainless steel swimming pool pole
  • Pool shock
  • Algaecide
  • Granular chlorine

Step 2: Sanitize

Start to prepare yourself for a bit of balancing, scrubbing, and sanitizing. To get black algae under control, you will need to make sure that there is no chance of it coming back. To start, you need to sanitize your pool maintenance tools. Take your entire swimming pool pole, all of the brushes, pool vacuum, and even any of the pool toys in your pool and spray them with a chlorine solution.

Ensure that all bathing suits worn in other pools, oceans, or lakes are washed properly and that there are no additional algae spores that could spread. The last thing you want to do is start this process and find out that you are adding more black algae to your pool along the way.

Step 3: Filter Cleaning

Remember that if there is a small spot of black algae in the bottom of your pool, your pool water, and your pool filters are infested as well. In order to get the proper water balance and no more algae spores in your pool, you will need to clean your filter.

Depending on what type of filter you have, this job can be a bit different. You will most of the time need to do a backwash and manually rinse a filter with a chlorine solution. You may have to do this again, but you will start with one filter cleaning for now.

Step 4:  Scrubbing

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Next is when the real fun begins. You are going to have to spend quite a bit of time scrubbing. We recommend starting with the pool brush and scrubbing away as much of the algae as you can. For the most part, the swimming pool algae tends to dig in a bit deeper when you have a cement pool. With a liner, the algae infestation never seems to dig in quite as badly.

Once you have spent some time scrubbing with a pool brush, you will want to scrub with a chlorine tablet. Wear gloves while you are doing this so that you don’t feel any irritation on your hand. Remember that some of these pool chemicals can be a bit tough on the lungs and the skin.

Take the chlorine table and cut it in half so that there is a rough side to it. The rough side of the chlorine will work almost like a wire scrub brush. Clearly, you will have to be sure that the surfaces are not being damaged with certain pool surfaces.

Combining the rough edge of the chlorine tablets and the actual chlorine in the tablet helps to loosen and kill the blue, green, or black algae.

Step 5: Shock the Pool

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In The Swim Chlorine Pool Shock
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  • Main active ingredient is 68% Calcium Hypochlorite (Cal-Hypo) for quick sanitizing

Next, you will want to triple shock your pool. If you normally use one bag of a shock for every 10,000 gallons, you will use 3 pounds of a shock for every 10,000 gallons. This is not the type of shock treatment you should be using on your pool daily.

Remember that weekly pool maintenance and removal of this type of algae will be a much different process. Shocking your pool will help start to break down the black algae and get it under control. You scrub the algae with the nylon brush and chlorine tablet first to open it up and allow the chemical into the algae spores.

Step 6: Balance Water

About 24 hours after you have shocked your pool, you will want to test the water and balance out any of the chemicals. At this point, you should also be looking for the black algae spots and to make sure that they have all disappeared. If you notice there are still more areas that the shock treatment did not deal with, you will need to scrub and then single shock the pool again.

However, if you did the proper amount of brushing initially, the triple shock should have worked. Make sure that all of your pool chemicals are balanced before moving on to the next step. Ph Levels are just as important to check as chlorine.

Step 7: Algaecide

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Some algae issues are going to go away with the proper pool maintenance and the appropriate chemical additions. However, for others, we recommend using an algaecide. It is not always necessary to keep algaecide in your pool; however, we recommend using it after an issue with black algae. One nice thing about algaecide is that it should help to keep algae away in the future.

Step 8: Brushing & Filter

We recommend brushing your pool and checking your pool chemicals each day for the next two to three days. Allow your pup to run at least 8 hours a day. If you can run it for 12-14, that would be ideal. This will help ensure that the product is running through the water and clearing out any of the additional spores in the water.

Step 9: Clean Filter

Remember we mentioned that you would have to clean your filter again once this process was complete. Now is the time to do that. As you have been working on getting the black algae out of your pool, your filter has been collecting quite a bit of the algae. You will need to rinse and clean your pool filter so that there are no additional issues with the algae starting back up again. This filter cleaning process is likely going to include a backwash.

Step 10: Analyze Pool

At this point, you should see no more black algae spots, and your pool water should be balanced as well. If for some reason you notice that there are spots that are starting to develop again, you will need to scrub them and then shock the pool. Remember that the scrubbing alone will not deal with the black algae alone.

Scrubbing loosens the algae and allows the shock to kill it. This job is a tough one, and it takes a long time for you to have your pool back to normal again. Follow our tips below to make sure that black algae never visit your pool again! 

Tips for Preventing Black Algae From Invading Again

The last thing you are going to want is for black algae to come back to your pool. Not only are you going to have to deal with more time out of your pool, but you will spend money on pool chemicals as well. There are issues that cause black algae to come up even in the cleanest of pools; however, these are some simple tips to keep black algae away for good.

Balance Pool Water

Part of being a swimming pool owner is testing and balancing the pool water. The more attention you pay to maintain your pool properly, the easier it is to deal with an issue when it comes up. Get a great water testing kit, and when things start to cause issues, get the water properly balanced as soon as possible.

Proper Pump Run Time

Running a pool pump is going to cost money, but it will keep your water clean. The pool pump is also going to be your pool’s best defense against algae in your pool. When the water is moving, those black spots are going to have a much harder time developing.

Shock Your Pool

Although shocking your pool is a great way to get your water back to normal, you will also need to shock your pool regularly. In the prime swim season, we recommend about once a week.

Equipment and Accessories Clean

Your pool maintenance and cleaning equipment can carry bacteria. You need to wash your equipment from time to time to ensure that it is not harboring any spores. The same goes for bathing suits and pool toys as well.

Rinse Bathing Suits

Before getting in the pool make sure that people rinse their bathing suits. It is truly best to wash the bathing suit completely before getting in the pool, but a good rinse will also help. Just be careful swimming from the ocean to the pool.

Vacuum and Brush Pool Often

General pool maintenance is important to keep black spots away from your pool. By using a vacuum and a brush in your pool a few times a week, it’s hard for the black algae in your pool to grow as strongly. If you are not going to remember to take care of your pool, look for a robotic or automatic pool vacuum that will do it for you. 

How to Get Rid of Black Algae in a Pool for Good

As you can see, this process is quite extensive. When you should be taking a relaxing swim in your pool, you are going to be scrubbing tiny black spots with a broken piece of chlorine. This is really not worth your time or energy; follow our tips to keep the black algae growth to a minimum and give yourself much more time to enjoy your pool. Don’t underestimate the amount of scrubbing and shock that you will use in your pool; this is a treatment that you will want to hit hard and get rid of it all at once.

Pricing on this page was last updated on 2021-07-23

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