Black algae spreading

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G

goober71

Well-known member
Jun 20, 2016
63
Houston TX
Hi All,
I have a 13200 gal plaster pool. The water was a little green at the start of the season, so I shocked it and have been keeping SWCG at 80%. Water is now clear and blue, but I have black algae spots all over the bottom and walls. I tried scrubbing them off, but they are pretty resistant. Some of them let off some green color and shrink, but others are pretty dug in!
How can I fix this? My chlorine level also drops to zero all the time, probably from the algae. It's only the black algae spots, no green algae after the shock.
I tried the chlorox algae treatment, but that did not do much.
Any help is greatly appreciated.

Thanks.

G
 
From your old thread, the pictures look more like copper and maybe some iron.

Light greenish stains on walls at deep end of pool

Hi All, We've had our pool for a couple of years now. Everything has been going well so far. This season, i'm seeing some green stains on the sides of the pool in the deep end (6ft). I've been pretty thorough with keeping the chlorine level up and brushing. Brushing will lighten the stains, but...
www.troublefreepool.com www.troublefreepool.com

Can you show the whole pool and the system?

Do you have a heater, ionizer or a mineral cartridge?

Have you ever used copper algaecide?

Can you remove the cartridges and show them before and after cleaning?
 
goober71 said:
I have been using Clorox Pool and Spa Xtra Blue 3" tabs this year.
Click to expand...
Those tabs contain copper.

Can you scrape any of the black stuff off?

Black algae is organic bacteria like a black mold that you would find on tile grout.

If it is black algae, it will scrape off like black mold and it will be dark green to blue or black.
 
JamesW said:
Those tabs contain copper.

Can you scrape any of the black stuff off?

Black algae is organic bacteria like a black mold that you would find on tile grout.

If it is black algae, it will scrape off like black mold and it will be dark green to blue or black.
Click to expand...
Yes, it is slimy to the touch and scrapes off with my fingernail with a dark green to black puff.
 

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goober71 said:
Yes, it is slimy to the touch and scrapes off with my fingernail with a dark green to black puff.
Click to expand...
This might be black algae.

You might have copper stains and black algae.

That is a difficult position because you need to SLAM to get rid of the black algae, but a SLAM can make the copper stains worse.

img_8987-jpeg.507010
 
You definitely have copper in the pool.

The algaecide is copper.

Can you show the whole pool and the system?

Do you have a heater, ionizer or a mineral cartridge?

Can you remove the filter cartridges and show them before and after cleaning?
 
In my experience a regular SLAM will not get rid of Black Algae. You will need to actually break off the BA first. Generally a wire brush is recommended since a nylon brush usually cannot break the surface of the algae.

If you have a lot, and your plaster is in good shape, I use a weak pressure washer. I think it does less damage to the plaster than a wire brush, but the experts here can comment on that. The pool water acts as a buffer from the pressure washer getting too aggressive. Generally I like a 15 degree nozzle. I put on a mask and snorkel and get in there and blast the algae away.

Then I get a 1 gallon pump sprayer that I fill with the strongest undiluted LC I can get and get back in the pool and spray those sections. You will need to so this a few times to make sure you kill all the roots of the BA.

Now this part is very important. You will need to run your FC hot for a few weeks. 20% of your CYA.

Also because of you have had BA once you should run FC hot pretty much forever. 15% of CYA works for me. I consider 10% my minimum.
 
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Katodude said:
In my experience a regular SLAM will not get rid of Black Algae. You will need to actually break off the BA first. Generally a wire brush is recommended since a nylon brush usually cannot break the surface of the algae.

If you have a lot, and your plaster is in good shape, I use a weak pressure washer. I think it does less damage to the plaster than a wire brush, but the experts here can comment on that. The pool water acts as a buffer from the pressure washer getting too aggressive. Generally I like a 15 degree nozzle. I put on a mask and snorkel and get in there and blast the algae away.

Then I get a 1 gallon pump sprayer that I fill with the strongest undiluted LC I can get and get back in the pool and spray those sections. You will need to so this a few times to make sure you kill all the roots of the BA.

Now this part is very important. You will need to run your FC hot for a few weeks. 20% of your CYA.

Also because of you have had BA once you should run FC hot pretty much forever. 15% of CYA works for me. I consider 10% my minimum.
Click to expand...
This is super helpful! Thanks! I’ll try the wire brush and see if I can break it up prior to running FC hot.
 
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