Pool Troubleshooting /
How to Get Rid of Black Algae in a Pool
Black algae usually needs aggressive brushing, vacuuming, circulation cleanup, and label-guided treatment. Persistent spots or equipment issues may need a pool professional.
Archive date: this article was written for PoolSkimmer on Oct 23, 2026 and given the earlier archive date of Sep 30, 2026 so the blog reads as an organized archive. It was not published on that date.
Dealing with black algae in a pool is no small task. It is a tenacious growth that will put down roots on the surface and form a shield against you, which is why the only real solution tends to be some aggressive brushing, a good vacuuming and an eye on your filtration and circulation.
How do you start getting rid of it?
Begin by looking at where the black spots have made themselves at home. You will often find them on rough surfaces like the walls, steps or fixtures. If you do not address the root cause in your pool care, they will be back in short order.
Here is the way to go about it:
1. Before you open, empty, or check a skimmer basket, make sure the pump is off. 2. Clear out any leaves and the like so the water can circulate as it should. 3. Put in the work to brush the spots thoroughly – we mean the seams, corners, fittings and steps. 4. Vacuum up what has been loosened to prevent it from settling back down.
With a plaster pool or other textured finish, dislodging the algae can be particularly difficult. A wire or stainless steel brush might be in order for certain surfaces, provided the manufacturer gives the okay. But be mindful not to use anything that would mar vinyl or a more delicate finish.
What allows black algae to return?
For the most part, it is a sign of subpar routine care. While chlorine, pH and filtration are key, how you correct them will be dictated by your pool’s design and what the water test tells you.
You want to be sure of the following:
- The skimmer basket is cleaned on a regular basis.
- The filter has been backwashed or cleaned per the manual.
- The pump is running long enough for proper circulation.
- You are testing the water with a kit you can trust and keeping the pH in line with your sanitizer.
A dirty cartridge or a clogged skimmer will compromise your filtration and let the algae stay. If the water is cloudy or you see the same spots reappearing, the job is not done.
Is chlorine or algaecide enough?
Not usually. Black algae can be resistant to normal maintenance once it has taken hold, so a simple chlorine treatment may not cut it. Algaecide has its place in the plan, but do not guess at a combined approach; stick to what the label and your pool manual say. Follow product labels and manufacturer directions for shock treatments, water testing, and chemical additions. And never mix chemicals or add them in an unapproved sequence. When in doubt over the safe treatment of your pool water, put it aside and call in a pro.
Things to avoid
There are some missteps that will only make removing black algae more of a chore:
- Giving the spot a light brush instead of a proper scrub.
- Rushing the vacuum and missing the debris.
- Overlooking the pump, filter or skimmer.
- Applying chemicals without having read the instructions first, including shock treatments and water testing or chemical additions.
- Swimming when the water is not up to snuff or there is an electrical issue with the equipment.
Put on the right PPE for handling chemicals and keep children and pets at a distance while you are at it. Do not swim in unsafe or uncleared water, and do not enter the pool if you suspect an electrical fault.
Time to call in a professional?
If the black spots are persistent, or if you suspect the algae is embedded in the grout or plaster, it is best to get some expert eyes on it. The same goes if you are not sure the finish can stand up to hard brushing, or if the circulation system is not performing as it ought to. A qualified professional can tell you if you are really looking at black algae or something else entirely. Should you have any reason to think there is an electrical fault, do not enter the pool until the equipment has been safely repaired.
Sources and further reading
- [Hayward: Weekly pool maintenance](https://www.hayward.com/maintenance/weekly-pool-maintenance)