How to Remove Black Algae From Your Pool


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If you see black spots growing in your pool, it is a sign of the beginning of black algae and you will want to treat it immediately. The longer you let it go, the harder it will be to eliminate it. Black algae generally penetrate porous pool surfaces like concrete and gunite. Once these surfaces are infested with black algae, it will take time and persistence to eliminate it. Black algae are generally not an issue with smooth-surfaced pools like fiberglass and vinyl. This guide provides a step-by-step procedure for eliminating black algae.


Step by Step


Step 1

ASSEMBLY TOOLS AND CHEMICALS - Buy the required tools and chemicals ahead of time to have them on hand for this procedure. If you have a concrete or gunite pool, you will need to buy a stiff brush like one with stainless steel bristles. The chemicals that you will need to buy are shock treatments and an algaecide.


Step 2

CLEAN FILTER - If black algae are in your pool, it's also in your filter. If you have a sand or DE filter, backwash and rinse your filter a couple of times. If you have a cartridge filter, pull out the cartridge and rinse it off thoroughly.

Step 3

BRUSH POOL - Next you need to brush off the black spots vigorously with as stiff a brush as you can use. If you have a concrete or gunite pool, use a stainless steel bristle brush. If you are one of the few that have black algae in a pool with a smooth surface, use the softer nylon bristle brush. Black algae have a protective cover over the algae roots that penetrate the porous surface of the pool. This barrier has to be removed so that the chemicals can get to all of the algae. Brush the algae spots three to four times a day for the duration of the treatment. Pay special attention to the pool's corners and around fixtures like the pool ladder.

Step 4

WEAR GLOVES AND EYEWEAR - Before you start handling the chemicals used here to treat black algae, put on a pair of heavy vinyl gloves and protective eyewear.

Step 5

SCRUB WITH TABLETS - Break a chlorine tablet in half and scrub the edge of the tablet over the black algae spots. For the areas you cannot reach, buy a tablet holder online that attaches to the pole of your brush.

Step 6

SHOCK POOL - Shock your pool with Sodium Dichlor using three times the normal dosage. So, instead of one pound per 10 000 gallons of water, use three pounds per 10 000 gallons.

Step 7

ADD GRANULAR CHLORINE - If you have a pool with a lightly colored surface, sprinkle Granular Chlorine over all the areas where it may settle on or near the black algae. Do not use Granular Chlorine in pools with dark surfaces as it may bleach the surface.

Step 8

ADD ALGAECIDE - Add one 32 oz. bottle of poly 60 algaecide per  15 000 gallons of pool water.

Step 9

RUN PUMP - If you have a pool with a light finish, leave the pump off for 24 hours to let the treatment set in. Then, after those 24 hours, run the pump an additional 24 hours the next day. For a pool with a darker finish, run the pump for 24 hours after adding the chemicals to prevent bleaching. During this 24-hour/48-hour period, continue to brush three to four times a day where the black algae spots were.

Step 10

CLEAN FILTER - Clean your filter again to rinse out any black algae residue.

Step 11

BRUSH POOL - Continue to brush where the black spots were for two to three days while the chlorine level is still high from shocking.

Step 12

RE-SHOCK POOL - If there is any indication of the black algae reappearing after three days, shock your pool again with a normal dosage - one pound per 10 000 gallons of water.Continue to brush where the spots were for two to three more days. Don't skip brushing. It is a key part of the treatment.

Step 13

MAINTAIN POOL CHEMISTRY - Once you have had black algae, it has a tendency to reoccur. It is important that you maintain your pool's chemistry and that you brush down the pool walls and floor once to twice a week. Note: Due to the heavy chlorine treatment, the chlorine level may remain high for up to two weeks.


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 Posted: 8/10/2021 

I have a 10K gal pool. We have a shallow area that is about 6 inches deep and I am getting some black algae dots in that area. I am using a PoolRX and when I had the water tested last week it showed 0.9 ppm copper. I shock weekly and try to keep Free chlorine between 1 and 2 ppm. Cyanuric is 42 ppm and I use liquid chlorine. My phosphates ran very high on this last test at 2500 ppb. I am using a steel brush in the shallow area where the dots appear but unsure what to do next. Water temp is at 85-87F.

InyoPools Product Specialist  Posted: 8/11/2021 

At a glance, I'd say your phosphates are not the cause of the algae, but they are definitely a catalyst to its growth. I'd try a phosphate remover like PhosFree Extra Strength along with your doses pool shock and a black algae-specific algaecide. A metal sequestrant would be helpful on the backend to control that copper level. 

 Posted: 4/29/2019 

I have drained my pool had black last fall, never could get rid of it all. Now I can see the black on several areas on the bottom I am patching a couple of holes I am going to acid wash first, wiil the acid wash be enough and I am going to paint it ?

InyoPools Product Specialist  Posted: 4/30/2019 

Hello Dale - yes, the acid wash should clear up any lingering algae.

 Posted: 3/21/2019 

We have had black algae since we moved into our house in November. I have tried everything the local pool store recommended. But I am loosing the battle. The only thing we feel left to do is replanted. Any other suggestions

InyoPools Product Specialist  Posted: 3/25/2019 

Bill - Have you tried silver algaecide? I used this a few years back when the normal black algaecides were not working and it did a great job.

Anonymous  Posted: 8/4/2021 

Where do you find silver algaecide? I only see black

InyoPools Product Specialist  Posted: 8/5/2021 

We usually carry silver algaecide but our supplier is out of stock at the moment. But a quick online search should bring up quite a few possibilities.

Anonymous  Posted: 3/25/2019 

No I have used algeatrane but not silver algaecide

 Posted: 1/7/2019 

Do you do the step by step all in one day? Like add all the chemicals in the same day at the same time or do I do one one day, and wait and do the rest the next? Just wasn't for sure if I was suppose to mix all the chemicals together at the same time?

InyoPools Product Specialist  Posted: 1/10/2019 

Hello Katie - You wouldn't want to mix all the chemicals at once. If you're using a black algaecide, follow the directions on the bottle. In most cases, the pH is adjusted first, followed by chlorine, and then the algaecide. You can separate each one by a couple hours. 

 Posted: 9/25/2018 

Hello MN - It sounds like you are doing everything correct. We would recommend using a silver algaecide to remove black algae. The silver algaecide seems to work well when the black algaecide does not.

 Posted: 9/21/2018 

I have been fighting w/ Black Algae for several weeks now on the floor of my pebble tech pool - I wire brush 2-3 times a day (so much so that I have loosened alot of pebbles :-( ), I scrub chlorine tabs directly on spots, have my FC up at 7+, and have done 2 diff treatments using 2 diff brands of 32oz Black Algaecides and, of course, cleaned filters prob every 3-4 days... It is not all over the floor of my pool but very prominent where it is - dark black clusters. Any ideas what I am doing wrong and why it won't go away...

 Posted: 8/16/2018 

Hello Shonda - Black algae usually occurs in small pits when the chlorine level is low. As far as getting rid of those spots, I recommend using a silver algaecide. This algaecide can be used with water in the pool.

 Posted: 8/16/2018 

As far as I know, the only way to treat black algae underneath an inground pool liner is to remove the existing liner and treat the algae. After the algae is treated you can roll on an algae preventative before installing a new liner.

Anonymous  Posted: 8/6/2018 

Help! The black algae is Under the liner of my 20X40 in ground pool. It shows up as big black areas in the pool. Scrubbing doesn't work. It keeps getting worse. I've tried shocking, algaecide but nothing works. It just stays there. This spring when I opened the pool, there was nothing on it, but now it's a mess. Is there anything I can do besides replacing the liner and treating the ground underneath (which I did a few years ago) Now the same problem is back.

 Posted: 7/30/2018 

We have just discovered we have black algae spots on the bottom of our light-colored gunnite saltwater pool--even though we have it serviced every week and it's only 3 years old. I'm now panicked as I want to get rid of this as quickly as possible before it gets worse. Are we better off draining the pool and scrubbing it and killing it? Also--what causes black algae? We've never had it before and are wondering if we did something wrong?

 Posted: 5/15/2018 

I have a fiberglass pool about 18yrs old. Yes, I have black algae. I live in the desert and did drain because our water table is so low I was told it's OK. I have been on my hands and knees scrubbing w/ chlorine tab and will follow your advice and refill and shock and treat w/ black algae killer (did not work first time from major chain. They told me pretty much hopeless and to replace pool!) and keep brushing. Hope your instructions are the same for fiberglass, although I know we are now supposed to get it. My luck. Thanks for the thorough instructions. I am encouraged.

 Posted: 1/7/2018 

john - I wouldn't recommend swimming in any water that contains algae. You run the risk of getting it into your eyes or ingesting it into your lungs.

 Posted: 1/4/2018 

What stages can we still swim in the pool?

InyoPools Product Specialist  Posted: 8/28/2017 

Gina - The process is the same for salt water pools.

 Posted: 10/1/2021 

Could you please recommend what chemicals to use to treat black algae spots in a pool with a salt chlorinator? I understand there are some chemicals that are not compatible with a salt pool.

InyoPools Product Specialist  Posted: 10/1/2021 

All of the chemicals and cleaners we mention in this guide can be used with traditional chlorine or saltwater pools. 

 Posted: 8/28/2017 

What about a Salt Water Pool? Is the process different?

InyoPools Product Specialist  Posted: 7/21/2017 

GUSGUS - We use to sell pools that held a chlorine tablet at the end to scrub algae on the bottom floor, but they were ineffective. You might see if you can find something like that on the internet. Other than that, I would agree with you. The most effective way to eliminate black algae on the bottom of a small pool would be to drain it, scrub it for two or three days, refill the pool and shock to 2-3 more days with frequent brushing and daily cleaning of the filter.

 Posted: 7/19/2017 

If I have black algae on the bottom of my pool some places hard to reach, would draining it and cleaning it be easier to remove the algae?

InyoPools Product Specialist  Posted: 7/7/2017 

Irene - You have to keep at removing the black algae. Initially, brush every black spot 3-4 times the first day then 2-3 times a day for the rest of the treatment period. Remember to clean your filter every day too.

 Posted: 7/6/2017 

I brushed some of the algae last night, today we'll finish and start chemicals, etc. do I have to re-brush the ones I did last night? i.e. how long before algae coated roots start again? I know I brush 3 times per day during treatment..

InyoPools Product Specialist  Posted: 7/5/2017 

The goat - Yes, you can use a steel brush on a pebble tec surface. The key to eliminating black algae is persistence. Black algae tends to embed itself into the wall of the pool. You have to brush it to remove the hard heads of the algae to allow the chemicals to get below the surface. Brush the algae spots, then use half of chlorine tablet to rub chlorine directly into the algae spots before adding chemical. Then repeat this process every day for 3-4 days.

 Posted: 7/3/2017 

I have a dark finish pebble tec pool which also runs on a DE filter. I got black algae as soon as we moved into this house and the filter broke. Can I use a stainless steel brush on a pebble tec surface? Any other recommendations as to getting rid of this stuff?

Anonymous  Posted: 6/23/2017 

Clear and straight to the point instructions. Worked great, thank you!

Anonymous  Posted: 5/25/2017 

Inyo pools got it right.
I should have done a before and after with photos. I did everything they said and my black algae is contained.


InyoPools Product Specialist  Posted: 4/8/2017 

Anonymous (algae) - I'm not sure what you mean by "My algae is 12 down" but here is a good link to a recent video on "How to Clean a Green Pool".

Anonymous  Posted: 4/5/2017 

My algae is 12 down what did do for that?

 Posted: 3/19/2017 

very helpful, contains a lot of useful, practical information.THANK YOU

Anonymous  Posted: 11/9/2016 

thank you...good tip..keep the good work..