SLAMMING to remove 2 year old Black Algae

Jun 1, 2015
houston, TX
Started SLAM Saturday morning to remove 2 years old stubborn black algae. In 24 hours with 2.5 hrs of steel wire brushing i would say 80% algae is gone. some of the algae still exist due to limitation of the brush reach in corners/edge of stones.
Please see pics attached with test results.

I would really appreciate comments/suggestions to be successful.


Apr 15, 2016
Central Florida
I've read hundreds - maybe thousands of posts, but yours is an instant favorite. I've battled black algae in my own Florida Plaster Pool.

Let's get to it:

1) Do you have a soft bristled brush too or just the metal wire?
2) Read this, written by Ben Powell:
As far as brushing . . . it's important, but persistence is more important than strength. I've seen folks attack it, as if one really, really hard scrubbing would get it all cleaned up. No such luck! If you want to get rid of black algae after it's become established, you have to commit to approaching it as a long term problem. Think weeks, not days.

(Of course, many pool stores will be happy to sell you any number of products that promise quick results. And, they'll also be happy to explain -- when you don't get quick results -- why it didn't work for *you*)

What's important is brushing enough to remove any dead top layer, or at least to scratch it, and expose the live algae to the chemicals in the pool. But it's much more important to brush some today, and the day after and the day after that, than to brush really, really hard today.

Another thing you need to keep in mind: black algae doesn't grow rapidly, and didn't appear in your pool suddenly. It's there because, day after day, the chemical levels weren't right. And, once it's gotten a start, it's unlikely you will EVER get rid of all the roots and spores penetrating into your pool. (I'm assuming it's NOT a vinyl or FG pool??) So, even if you 'get rid of it' for now, it will come right back unless you learn to maintain proper chemistry day after day in the future.

Now, you didn't post test results, or tell how you've been treating your pool, so I don't really know what you've done wrong. There are numerous possibilities; here are a few of the more common:
Low, or inconsistent, chlorination.
High pH, not compensated for with higher chlorine.
High stabilizer, not compensated for with higher chlorine.
Poor circulation, or not running the pumps enough.
Porous or damaged plaster, not compensated for with higher chlorine.
Keep in mind that a single day -- or even week -- of one of these problems wouldn't lead to black algae. It just doesn't grow that fast.

So, what you really need to first, is figure out what's been going wrong, and learn how to correct that. Otherwise, anything you do to get rid of the algae will be only very temporary in effect! Fortunately, as many PoolForum members can tell you, doing it right is easier and cheaper than doing it wrong, once you learn how!

Meanwhile, except for the trip and fall hazard from the black algae, there's no reason to not use the pool while you work on the problem . . . as long as you have chemistry that's adequate for sanitation

Once you figure out what you need to correct, and take care of that, the solution is pretty straight forward:
Brush regularly.
Maintain chlorine levels 50% higher than you'd otherwise need to maintain.
Using polyquat will help some, especially if you can FREQUENTLY brush hard. But, it's still going to take weeks, as a rule, not days.
3) be sure to take from that the explanation that it more about # of brushings (and over time) and not force of brushings, so don't try to literally scratch the stubborn spots away - think of it as peeling a layer off, bleaching it for some time, peeling another layer off, bleaching it, repeat
4) after all this is said and done and you let FC come back down to "target FC" on [FC/CYA][/FC/CYA] - do yourself a favor and treat the lower number of the target range as the minimum - for at least this summer. Pools surviving BA deserve a FC cushion above what a non-BA pool would have
5) Consider a smaller 5" wire brush like this $7.5 one or this $10.99 one on Amazon Smile (Amazon donates to TFP) if you think they will help you get the corners better without damaging the plaster. If not, just get yourself a soft bristled corner brush from hardware store or Amazon Smile. Alternatively, and I've never heard anyone do this yet - but I almost did - so this isn't TFP approved - is to go to discount tool store or hardware store and buy a small, handheld, almost super toothbrush sized steel bristled brush, usually for polishing/cleaning small parts.
6. Keep going on this, but don't try to force the results - as you said, it had years, so it isn't likely to be fully resolved in days.

Did I address everything? There was a lot going on. Questions? Feedback?

- - - Updated - - -

Also, just to remind = PH test is invalid when FC is above 10.

We suggest swimming when FC is under shock per cya ([FC/CYA][/FC/CYA]) but I understand if you wanted to overshoot the shock up towards the Yellow/Mustard shock levels at times - but reminder that those numbers were only meant to be held for a day or two as part of that protocol. You may just want to do the in pool work when FC is under regular shock fc, just to be safe. And you may want to stay around shock fc, then do a MA/YellowA higher shock either once pre week or just at the end of the current brushing push. Up to you and how well your plaster is fairing.

small $2 brush example link:,Air,RotaryShopEquip-_-3474873:Lincoln_Electric&CAWELAID=&kpid=3474873&CAGPSPN=pla{ifdyn:dyn}&k_clickID=2d38c0da-4936-46a1-a10f-6ab8ec4f5976&msclkid=5e5c4d0d09b11e19e73717f4e0b31a72

Jun 1, 2015
houston, TX
Thank you for the quick response. I will keep in mind about more frequent brushing instead of less frequent hard brushing.

I would say 90% of algae is gone and will buy small brush to reach deep corners and brush it. will post pics soon.


Well-known member
Nov 23, 2017
Port Orange, FL
Is that a water feature that appears to be made of stacked stone or decorative concrete? If so, that could be harboring some nasty stuff that could recontaminate the pool. I had a similar issue so bad I removed the water feature so I wouldn't need to worry about it or try to keep it disinfected. I think I'd spray a strong chlorine mixture over the water feature, coping and anything else that might harbor anything that might not be exposed to a slam. Not once but a few times over a few days just to be more certain it's not part of the problem.
Apr 15, 2016
Central Florida
Great catch! Water features and finish above waterline are places where algae loves to live! Algae needs some sunlight to really thrive, so you're mainly focused on places you can see, thank gosh, and just getting the shock fc water through the whole system. There are other threads about water features and water falls and black algae or algae that you can search for. Hopefully the experts have chimed in, if not, just ask your questions here and if we can't answer them, we'll pull in more people.
Jun 1, 2015
houston, TX
That water feature is made of the stacked stones. Every time i try to scrub underneath the water feature, some algae do come off. I think Algae survived underneath on light though direct sunlight not available. Floor is clear of algae but sides do have some tiny spots of algae which i am scrubbing it once a day.