How to get rid of black algae in pool? is the most commonly asked question because no one should swim in your pool until it’s gone.
The good news is it’s totally possible to kill black algae.
So here is a step-by-step guide…
What are Black Algae and Why is it in Your pool?
When you think of algae, you probably think of something green. Black algae is actually a bacteria called cyanobacteria. It’s also called blue-green algae, but the bacteria can appear black.
So how does this kind of algae end up in your pool?
Well, someone probably swam in a natural body of water like a river, lake, or ocean and they didn’t wash
their swimwear afterward, bringing those black algae into your pool.
What Do Black Algae Look Like?
Black algae look like mold. If you notice a bunch of tiny black dots or big clumps of mold forming on your pool surfaces, you may have black algae and it can sometimes look bluish-green.
Here are a few ways to recognize black algae in your pool.
- There are black or blue-green spots and clumps with raised heads attached to your pool surface. They don’t float freely in the water.
- it’s on rough or porous surfaces. Black algae seldom form on pools with fiberglass or vinyl liners. It likes to grow in porous surfaces like concrete, plaster, or gunite pools.
- it doesn’t brush off the wall very easily with your regular pool brush or even a metal algae brush.
- it can be scraped off the pool surface even though it might take some extra work. Pool stains, on the other hand, cannot be scraped off.
- it shows up even if your pool water is balanced, sanitized, and filtered because it enters your pool from an external water source.
These are the five signs that indicate the presence of black algae in your pool.
How to Get Rid of Black Algae in Pool?
Treating black algae isn’t the same as treating green algae. It actually takes a lot more effort and persistence, but it is possible to kill.
So before you begin, you’ll need the following supplies.
Depending on the type of filter you have, you’ll need a backwash hose, filter sand, DE powder or a replacement filter cartridge.
Okay, let’s get cleaning.
Backwash The Filters
If you only have little black algae, you can just backwash your standard DE filters or rinse your cartridge filter.
However, if you have a lot of black algae use filter cleaner rather than plain water. You may also wanna completely replace the filter medium or cartridge to get rid of any bacteria.
Test The Pool Water & Check Chemical Balance
Test and balance the water. Use pool water test kit, test strips or a liquid test kit to test your pool water. Focus on alkalinity, pH, and sanitizer.
Alkalinity should be between 100 and 150 parts per million with 125 parts per million being ideal.
pH should be between 7.4 and 7.6 with 7.5 being ideal.
Chlorine should be between 1 and 3 parts per million or the proper range of whatever type of sanitizer that you use.
Adjust your levels before moving on to the next step.
Brush The Pool
I mean brush the pool as you’ve never brushed before. Brushing black algae loosens
it from the pool surfaces and puts it into the water where chlorine will be able to kill it.
Use stainless steel bristled algae brush to get into those cracks and crevices and really dig out that algae.
If you have a fiberglass or vinyl liner pool, you wanna use a nylon bristle brush, but you’re gonna have to use twice as much elbow grease.
Scrub The Black Algae Spots
No matter how well you just brushed your pool, you’ll probably still see some black algae spots, you’ll have to scrub those by hand.
We recommend using chlorine tablets to scrub the remaining algae patches. This only works in concrete plaster or gunite pools.
Do not do this on a fiberglass or vinyl liner pool.
Not only are you scrubbing off the algae, but you’re also applying chlorine which can start killing the bacteria. Follow these simple three steps.
- You’re gonna wanna put on chemical-resistant gloves and wear protective eyewear.
- Break a three-inch chlorine tablet in half.
- Hold it firmly and scrub the black algae with the broken edge. Don’t worry if you don’t get every speck of black algae off the pool surfaces.
Brush The Pool Again
Give the pool another pass with the brush.
Quadruple Shock The Pool
Now that you’ve brushed as many black algae off as you can, you need to kill everything that’s floating in the water.
A regular dose of shock won’t kill black algae, so we highly recommend using calcium hypochlorite shock.
Follow the manufacturer’s instructions to determine the correct dose for your pool’s volume, and then multiply that by four for a quadruple shock.
And here’s a tip, place all of your pool maintenance equipment you’ve used in the shallow end of your pool to sanitize it during the shocking process.
Remember to shock your pool at dusk or at night.
If you shock your pool during the day the sun’s gonna eat up most of that chlorine and it won’t do its job correctly.
Run The Pump
Run the pump for 24 hours to disperse the shock and kill all that black algae.
It may come back to cloudy water, but that’s gonna be normal.
Brush The Pool Again
During that 24-hour period, while the chlorine level is at an all-time high.
You wanna brush the surfaces ideally three to four times to get any remaining black algae off the walls and floor and into that extra-chlorinated water.
Clean The Filter
The first time you’ve cleaned your filter was to remove any live bacteria. When you ran the pump after shocking the filter probably accumulated bits of dying black algae like it’s supposed to.
now, simply backwash your sand or DE filter or rinse your cartridge filter, and to be on the safe side you can use a filter cleaner.
Shock The pool again, if necessary.
If you still see any remnants of black algae in your pool after doing all of those steps, you’re gonna wanna shock it again.
This time, you can just use a double dose.
Run the pump again
You can run the pump for eight to 12 hours, but to be on the safe side. We recommend running it for another 24 hours.
Brush The Pool
Yep, I know you saw that one coming. Brushing is really the only way to get rid of all the bacteria off your pool surfaces so you wanna make sure it doesn’t come back.
Do not skip the brushing.
Check The Chemical Balance
Test and balance water. After all that work, your pool should finally be free of black algae. Test the water and add the appropriate chemicals as needed to bring all the levels back where they should be.
Keep An Eye Out For Stragglers
Over the next couple of weeks keep a close eye on your pool for any signs of black algae returning.
Even with all that shocking and brushing, you may have missed a few bacteria that will start to grow again.
If you do see a small spot reappear, brush it off, and scrub the spot with a broken chlorine tablet and then give your pool another normal dose of shock.
How Do you prevent black algae in the future?
The first line of defense is to always wash your swimsuits, floats, shoes, toys, and anything that you’ve may have used in a natural body of water before it goes back into your pool.
Swimwear should be washed in a washing machine, and all pool toys must be scrubbed and sanitized. You can use a spray cleaner that contains bleach or dilute a tablespoon of bleach into a gallon of water.
Make sure to keep your pool properly balanced and sanitized to prevent any future algae growth.
- keep your alkalinity, pH, and sanitizer levels in the recommended ranges at all times.
- Run your pump and filter at least eight to 12 hours a day all season long.
- Regularly vacuum and brush your pool. Shock your pool at least every week.
- Keep your pool equipment clean including skimmers, hoses, ladders, steps, the diving, board, slides, solar blankets, and your safety cover.
- Make sure anyone using your pool rinses off first. If not, they’ll be the ones doing all the scrubbing and brushing if those black algae come back, mark my words.
And that’s it, that’s the long process of how to get rid of black algae in your pool.