How To Get Rid Of Black Algae In Your Pool

Black algae are small living organisms that penetrate porous pool surfaces like gunite and concrete. The black algae roots grow into the cracks of the plaster where they lock-in and don’t like to let go.

There is an effective way to treat black algae and eliminate them from your swimming pool water. The problem with black algae is that it has roots that grow into the cracks of the inground pools plaster. With an above ground pool, you will get the black algae that start to form together as clumps in the water. The pool cleaning process will be very much the same for both types of pools.

This is what I have been able to do to treat black algae and stop it from returning and the pool chemicals that I have used.

Before you begin. These are the Supplies you will need.

  • Backwash hose
  • Filter cleaner
  • Filter cartridge
  • Test strips / Liquid test kit
  • Algae brush
  • Chemical-resistant gloves
  • Safety goggles
  • Chlorine tablet holder
  • Telescopic pole
  • Calcium hypochlorite shock
  • Pool Shock Treatment
  • Algaecide
  • Chlorine Tablets
  • Granular ChlorineClean your filters
  • Muriatic Acid
  • Sanitizer

1. Clean Your Pool Filters

When you have black algae in your pool, you definitely have black algae in the pool filter. If you have a DE or a Sand filter, I recommend that they are back washed and rinsed at least twice.

If you have a cartridge filter and the black algae infestation is bad then I suggest removing and rinsing the filter with filter cleaner or even replacing the filter.

2. Brush The Pool Walls And Floor

If your pool surface is gunite or concrete. Then I suggest using a very stiff-bristled brush or a stainless steeled bristled brush.

If your pool surface is fiberglass or vinal. Then I suggest using a soft-bristled pool brush.

Now that you have chosen a suitable brush for your pool surface, its time to get brushing. Now you need to brush the black algae from the sides then the bottom of the pool.

What this does is loosen the black algae from the pool wall and floor surfaces and puts it into the water.

This is where the pool shock will take over and kill the black algae.

Remember the black algae is very stubborn and grows into the cracks and tiny crevices of the pools plaster. That’s why, if after the first round of brushing you still see some black algae spots left. Brush for the second time.

If after the second round of brushing there is still black algae spots then its time to use the chlorine tablet.

Put on your chemical-resistant gloves and eye goggles. Break a 3-inch chlorine tablet in half and fit it into a Pentair Algee-Gon 3 Inch Chlorine Tablet Holder with the broken tablet edge facing outwards. Attach a pool pole to the chlorine tablet holder if necessary.

Now brush those areas that were not removed by normal brushing with the chlorine tablet. What the chlorine tablets do is apply chlorine directly onto the black algae which penetrate into the roots of black algae which start killing them off immediately.

3. Shock The Pool Water

Now that all the black algae are mixed and floating in the water it is time to shock treat the pool water. I highly recommend these pool chemicals, calcium hypochlorite shock to kill the black algae. Or you may use granular chlorine.

Follow the manufacturer’s instructions to determine your pool’s volume for the correct amount of chemicals needed for shock treatment. Then either increasing the shock level of treatment to 30 ppm or times the amount by four.

If you are not too sure how much water your pool holds?

Then you can use our pool volume calculator to work it out.

It’s a good idea to put all the pool equipment you used eg tablet holder, algae brush, pool pole leaf skimmer, etc into the shallow end so that they can be sanitized during the shocking process.


Remember its best to shock your pool at sunset or at night. If you shock your pool during the day most of the effects can be lost due to the sun eating away at the chlorine before it has a chance to kill the black algae.


I would recommend adding 1Quart of Algaecide. This chemical kills and prevents algae from growing again. This helps prevent further outbreaks of black algae.

4. Run The Pool Pump

To get the shock treatment chemicals to mix with the black algae you will need to run the pool pump for the next 24hours continuously. The pool water may turn cloudy, but that’s normal.

Continue at regular intervals to brush any remaining black algae off the walls and floor of your pool. I had to brush another 4 times to make sure there were no remaining black algae spots.

5. Re Clean The Pool Filters

When the pool pump is running all that black algae is going to be sent through the filters. You will have to clean the filters again after the 24hour pump cycle to get rid of the dead black algae.

Rinse with water or use a cartridge cleaner for the filter when dealing with black algae. It also depends on the severity of the infestation that you had.

The Sand and DE filters will need to be back washed and rinsed well to make sure all black algae spores are gone.

It is possible that the filters might need to be cleaned for the 3rd time after 48hrs have passed.

6. Check For Black Algae And Shock Pool Again If Necessary

After the initial shocking of the pool. Running the pump for 24hrs and cleaning the filters. If you still see black algae on the pool surfaces, shock treats the pool again.

When you shock the pool this time only double the recommended dose. Run the pool pump for another 24hours. Continue with the brushing. At least twice a day.

7. Test And Correct The Balance Of The Pool Water

After about 2 days your pool water should be free of all black algae. Using the correct test kit, test the water PH and Total Alkalinity chemistry levels and add the appropriate chemicals as needed to bring all the levels back to where they should be.

8. Now That The Black Algae Has Gone

I am sure you are exhausted after that job. I never want to do that again.


Regular pool maintenance every week is so important. Such as cleaning out the filters, running the pump, testing the water chemistry, vacuuming the pool, brushing the pool, etc.

This little bit of work when the pool stays clean is much better than a 2day nightmare. A clean pool is easier to maintain than a dirty pool.

Weekly maintenance keeps your pool safe for your family and pets.

Will Chlorine Kill Algae In a Pool?

Will Chlorine Kill Algae In A Swimming Pool?

Normally Yes. Chlorine kills algae and bacteria by a chemical action called oxidation.

Why Is Chlorine Used In Swimming Pools?

Chlorine is used in swimming pools to act as a disinfectant and to stop the growth of algae.
Without chlorine, most pools would be green within a few days.
It takes chlorine to kill algae. An algaecide is usually used in conjunction with a chlorine shock to kill algae.

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Chlorine helps pools by killing off the algae microorganisms. It also helps in keeping down the growth of algae.

Warm pool water with a temperature over 80° F and chlorine levels below 1 ppm contribute to algae growth. If there is a high concentration of phosphates in a swimming pool, you can get algae growth even if the chlorine level is higher than 1 ppm. The pool temperature can be checked by a floating solar-powered pool temp thermometer.

What Causes Algae In A Swimming Pool?

The lack of proper swimming pool water filtration and when chlorine levels have been allowed to drop too low. Or when the chlorine is not acting effectively because the water is out of balance, or the pool water has high levels of stabilizer (cyanuric acid). Hot and humid sun conditions as well as if the pool has been used a lot for swimming.

Algae are spores that are blown into the pool or carried into the water in other ways, They then multiply into blooms when the conditions are ideal for them.

Algae are spores that are blown into the pool or carried into the water in other ways, They then multiply into blooms when the conditions are ideal for them.

These tiny microscopic plants feed on nutrients in swimming pool water.

How To Get Rid Of Green Algae In Your Pool

Green water or floating green algae in a swimming pool is a common problem. Several chemicals can be used for treatment. By regular swimming pool maintenance, you can prevent green algae from returning.

How To Use Chlorine To Kill Green Algae In Your Pool Water

If your swimming pool water contains clumps of visible green algae, then there isn’t enough chlorine in the swimming pool. “Shocking” the swimming pool with chlorine is the most effective way to kill existing green algae and bring your swimming pool back to life.

Usually, this works within a time period of 1–3 days, but if the swimming pool conditions are poor, it could take up to a week.

How To Remove Green Algae From The Pool Walls


Brush the swimming pool walls and floor. Remove as many green algae as possible. This will reduce the time needed to kill and clear the green algae.

Pay particular attention to the swimming pool steps, ladders, and other areas where algae tend to form.

Make sure that the brush matches your swimming pool. Steel brushes work well for concrete swimming pools, while for vinyl and fiberglass swimming pools nylon brushes are preferable.

Test The pH Level Of The Water


Balance the pH by adding either an acid or a base to bring the level to just around 7.8 before treating the pool. This is at the high end of the range that you would normally have in your pool, but when you treat it for algae, it is necessary as this increases the efficiency of your chlorine and therefore reduces the growth of green algae.

Here’s how to balance the pH level: Turn on your swimming pool pump to circulate the chemicals throughout the pool. Correct the pH level either by increasing the sodium carbonate pH or by lowering it with sodium bisulfate.

It’s more accurate to use test kits that have tablets or droppers than paper test strips. If the pH levels return to normal but total alkalinity exceeds 120 ppm, check the instructions on the pH reducer label (sodium bisulfate) to reduce the total alkalinity to between 80 and 120 ppm.

Choose a suitable chlorine Shock product. Do not use the chlorine that is used for regular swimming pool treatment. Ideally, liquid chlorine for swimming pools should be used. Sodium hypochlorite, calcium hypochlorite, or lithium hypochlorite should be included in the product.

If you have hard water, avoid calcium hypochlorite.

Avoid granular or tablet chlorine products that contain large quantities of stabilizers that should not be added to the pool. Check the product for instructions on how much to use.

Use twice the recommended amount to fight green algae for a regular shock. Use triple the amount if the water is green with thick suspended algae, or even quadruple if the steps are not visible. Add the shock directly to the swimming pool edge with the swimming pool pump running.


Because UV rays break down chlorine in sunlight, add at night as this is when the chlorine is most effective.
Before switching the pool pump on, make sure that the weir basket and pump filter are clear of all debris. If not this will lengthen the filtering process of the green algae.

Check the swimming pool after the pool pump has run for 12–24 hours.

Dead algae turn’s white or gray, either the algae are suspended in the water or it settles at the bottom of the swimming pool. Remember to vacuum the dead algae from the swimming pool floor.

When vacuuming, make sure that the multivalve is on backwash so it does not block the filter. It is advisable to reclean the weir and pump filter after 24 hours as green algae will now be trapped in these parts.

Whether the green algae is dead or not, test the swimming pool water for chlorine and pH levels.

If the level of chlorine is higher (2–5 ppm) but the green algae is still there, keep these levels constant for the next few days. If the chlorine levels have risen but are still below 2ppm, then the next evening “Shock” for a second time.

If the chlorine levels have not changed significantly, your swimming pool is likely to have too much cyanuric acid (over 50 ppm). This comes from using granulated or tablet chlorine, and your chlorine condition can be “locked”.

The only way to fight this is to repeatedly “Shock” or partially drain the swimming pool.


The chlorine strength can also be used up if leaves or other unwanted dirt is in the swimming pool as well as if the pool has not been used for a long time. So make sure that the unwanted dirt is removed. It may take a full week and several “Shock” treatments for the swimming pool to come right if this is the case.


The chlorine should kill the green algae over the next few days. Test the water daily to confirm you have the correct amount of chlorine and pH. A well-maintained swimming pool has these values: free chlorine: 2-4 ppm, pH: 7.2–7.6, alkalinity: 80–120 ppm and calcium hardness: 200–400 ppm, respectively.

Small differences are common, so there should be no problem with a slight deviation.

If you still have trouble with the green algae, add coagulant or flocculant so that it clumps the algae together. Once there’s no green color left in the pool, vacuum up (set multivalve to backwash) all the dead algae until the water is clear.

You could let the filter handle it, but make sure the filter is clean first. If you do not thoroughly clean the filter, the filter can get blocked by the dead algae.

Check for the proper functioning of the swimming pools water jets.

They should point at an angle in the water so that the water moves in a spiral pattern around the swimming pool to get the most effective circulation for filtration.


Adding flocculant or coagulant is the fastest way to make your swimming pool water look good, but it’s not safe to swim in this water. Follow this with a treatment of chlorine “Shock” to sanitize the pool and do not swim in the pool until the levels of chlorine and pH return to normal.

How To Treat Pool Water With Algaecide

Algaecide will surely kill your green algae, but it may not be worth the side effects and expenses. Some algaecide products, especially if you have black algae as well, are not powerful enough to treat an existing problem.

Ask a pool store for help, or find a 30 percent + active ingredient product.


Quaternary ammonia algaecides (“poly quats”) are inexpensive but foam your water. This is annoying to many people. Algaecides based on copper are more effective but costly. They also stain the walls of your pool.

How To Remove Phosphates From Pool Water

In water, algae feed’s on several nutrients, particularly Phosphates. Phosphate test kits are available to test swimming pool water for these chemicals.

Use a commercial phosphate remover from a pool store if they are in the water. When adding Phosphate remover to swimming pool water, let the pool pump run and the water must circulate through the filter for 24 hours.

About 300 ppm is an executable level unless you have recurring problems with green algae. Then this level should be lowered.

Clear Swimming Pool Water.

Keeping Your Swimming Pool Water Clear Is Important

If you maintain your pool chemistry levels, algae should not grow. Test the swimming pool for free chlorine, pH, alkaline and cyanuric acid levels on a regular basis.

The quicker a problem is detected, the easier it will be to deal with. During the swimming season test at least twice a week.


A preventive algaecide can be added to a swimming pool when conditions are normal. Algaecides are best used in small, weekly doses. This will kill populations of algae before they grow. Too much algaecide can cause foaming or staining of your pool walls.