Advice for black algae?

Mastiff

Member
Aug 24, 2011
12
I think what I have is black algae. It appears as small black spots or dark black areas within the texture of the pool walls. I've been fighting it for over a year now. And despite fairly constant attention it has at times been very bad, appearing as large areas (many square feet) where the pool wall is gray instead of white (gray because I can brush the darkest black of it away). Phosphate remover helped and I thought I had it defeated over the winter. I had the chlorine levels off the chart for a full month. Then summer came and it's back in full force. It does not come off with a wire brush, but I can get in there with a pressure washer and painstakingly remove most of it. Since I can only fully remove it a square inch at a time, I'm sure I never totally get all of it.

I'm to the point where I suspect the only realistic option is to do something like fully drain the pool, apply some nasty chemicals, maybe let it dry out for a long time? I hope there's some other option. Looking around the internet makes it seem like I'm the only person who has ever had it so bad.
 

Rancho Cost-a-Lotta

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TFP Guide
Apr 10, 2018
3,698
Rancho Cucamonga, CA
Pool Size
18375
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45
Have you confirmed it is black algae? Scrape some of the stain with your fingernail. Wipe it on a white piece of paper or index card. You should see a green stain.

Have you seen this article from Pool School?


Do you have a TFP recommended test kit?
 

Mastiff

Member
Aug 24, 2011
12
Have you confirmed it is black algae? Scrape some of the stain with your fingernail. Wipe it on a white piece of paper or index card. You should see a green stain.

Have you seen this article from Pool School?


Do you have a TFP recommended test kit?

I'm not certain it's black algae, but it looks much like the pics on this site: How To Remove Black Algae From Your Swimming Pool | Kill Black Algae

For some reason that Pool School link doesn't go through. It just goes to the main blog page...

And no, I don't have the TFP kit, but I think I'm not at a point where I need that detail yet. I had the Home Depot strips off the chart for a month or more. I'm pretty sure super high is super high to everyone.

One suggestion I saw on the linked site, which I thought of but forgot, is that spores could be in my filters even when I get the pool itself in decent shape. I guess the question is whether to invest the $$$ in all those cartridges before it looks clean, or wait until I (maybe) can get it looking clean. Kind of a chicken/egg issue.
 

Rancho Cost-a-Lotta

Silver Supporter
TFP Guide
Apr 10, 2018
3,698
Rancho Cucamonga, CA
Pool Size
18375
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45
I'm not certain it's black algae, but it looks much like the pics on this site
Try this...
Have you confirmed it is black algae? Scrape some of the stain with your fingernail. Wipe it on a white piece of paper or index card. You should see a green stain.
For some reason that Pool School link doesn't go through. It just goes to the main blog page...

For the TFP Black Algae article, click on Pool School on the menu bar, then click the "view all" button int the "Welcome to Pool School" box and scroll down to the article.

TFP recommends test kits that utilize Taylor reagents. In the link below, you'll find an article on recommended test kits.

 

duraleigh

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Mod Squad
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In The Industry
Apr 1, 2007
35,114
Sebring, Florida
Before you start "stabbing" at the cure, identify the stain as positively as you can. From your description I simply have no clue as to what it is. Rancho's suggestion of scraping some off and then seeing if it turns green smeared on a white piece of paper is probably the best test.

I will add that black algae is probably the most mis-diagnosed issue we have on the forum.
 

Mastiff

Member
Aug 24, 2011
12
Before you start "stabbing" at the cure, identify the stain as positively as you can. From your description I simply have no clue as to what it is. Rancho's suggestion of scraping some off and then seeing if it turns green smeared on a white piece of paper is probably the best test.

I will add that black algae is probably the most mis-diagnosed issue we have on the forum.
Thanks for the reply. I can give it a shot, but I haven't been letting it get so out of hand that it has significant "volume" for me to scrape up. I don't know if it ever got that thick. It lives in between the pebble-tek surface.
 

Katodude

Silver Supporter
Aug 22, 2017
2,049
West Palm Beach/Florida
Pool Size
15000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
And no, I don't have the TFP kit, but I think I'm not at a point where I need that detail yet. I had the Home Depot strips off the chart for a month or more. I'm pretty sure super high is super high to everyone.

Nope. Strips are totally useless. And yes you are exactly at the point where you need that detail.

If what you have is black algae and to me it sounds like it you will need a proper test kit (you would need one if you did not have black algae but I digress).

Use your pressure washer like you did to remove the algae. Then get a 1 gallon pump sprayer and hit those spots with the highest dose of LC you can find. Then keep your pool FC at 20% of your CYA for a few weeks (this is where you need a proper test kit).