Drained pool to rid of Black Algae question

[Racerx143]

I have a small (10,000ish) gallon concrete pool in Florida. A group of people came to my house right from the ocean and within a few weeks I started seeing black algae forming in the pool. Went to pinch a penny pools and they sold me a stainless steel brush, a qt. of Sun Coast Metal Control (from their web site: Suncoast Chemicals Metal Control is a specially formulated sequestrant that helps prevent and remove copper stains from swimming pools, as well as other minerals and metal deposits. Metal Control works on all pool surfaces and when used regularly will help prevent new metal stains from forming.) They told me this would help loose up the outer shell/coating of the algae before scrubbing it. They also sold me quart of SUPER BLACK ALGAECIDE for killing the stuff. I did everything just like they told me. Most of it appeared to go away except for a few very small spots that I just couldn't kill. Within a week it started coming back right where it was before and just as bad. I did it all again with the same result. Needless to say, that gets expensive and frustrating. That all may be a little long winded considering my real question. Since my pool is so small, draining it is not an issue. I am wondering what would be my best approach, (other than replastering) to kill this stuff now I can get right to it. Chlorine wash? Acid wash? Something else?

[Teapot]

They sold you a sequestrant and they sold you a COPPER based algaecide. Time to find another pool company! If it is black algae it has a tough outer shell, you need to an abrasive to scrub through the outer shell of the algae and raise your free chlorine level to shock level and hold it there until it's all dead.
What your shock level should be is determined by your water test results in particular the stabiliser level. Please test this (NOT with dip strips) and pop back and we'll help some more.

[Denniswiseman]

As Teapot says please get a full set of numbers, it may be not necessary to drain
FC:
TC:
pH:
TA:
CH:
CYA:
Pool chemicals:
My pump & filter:

[Teapot]

Looks like another drifter passing by. I think in future I will wait until the second post comes in to see if they are genuine, life's too short to waste on posters who don't come back.

[rfoster143X]

For some reason, I was not notified at my regular email that anybody had responded, on top of that just getting over the flu so this has not be a main concern. Just now checking back. Anyway....

I was not clear in my post that the pool is currently drained and I am looking for the best solution for dealing with it dry.

[maiphuonganh]

When the pool is infected with black algae you need to persevere, use a steel brush to scrub, you need to scrub because black algae are easy to come back, do not use chlorine shock because black algae are resistant to chlorine, you Can use chemicals to kill algae barquacil

[Teapot]

For some reason, I was not notified at my regular email that anybody had responded, on top of that just getting over the flu so this has not be a main concern. Just now checking back. Anyway....

I was not clear in my post that the pool is currently drained and I am looking for the best solution for dealing with it dry.

Ok, welcome back. As it's now dry you can get to work on it. scrub the marks and provided it's not a liner/GRP pool a stainless steel brush not ordinary steel will remove the top. Then treat with chlorine dioxide if possible as that gets into the bacteria and destroys it.

[Denniswiseman]

While it's drained you might as well do an acid wash as well to remove any metal staining, that will also work on the algae
You would need basic protection to prevent damage to yourself

[rfoster143X]

I have a SS brush. I used it in my attempts while the pool was filled. My pool is Concrete/Plaster. I will look into the Chlorine Dioxide. Thanks.

As far as the acid wash.. Last time I did a wash.. 2 years ago.. I was cleaning the pool since it had sat for a about year with a broken pump and was green, a total wreck. I started with muriatic acid and it didn't seem to do a thing. I know that it will etch the walls and maybe thats what I need to kill this stuff. But I decided to try liquid Chlorine, it just washed the discoloration right away so I used that instead of the Acid. Thanks for the input.

As far as the cause. I want to blame it on the day we got into the pool straight from the ocean. It did happen right after that and in the 15 years I have had this house, I have never had black algae before and to the best of my memory, have never had a large group over straight from the beach to my pool. But... I have a concrete deck around the pool and I have noticed it has places that look like black algae or mold I am guessing from run off from my roof. Anybody understand how this stuff starts to begin with?

[Denniswiseman]

I have a SS brush. I used it in my attempts while the pool was filled. My pool is Concrete/Plaster. I will look into the Chlorine Dioxide. Thanks.

As far as the acid wash.. Last time I did a wash.. 2 years ago.. I was cleaning the pool since it had sat for a about year with a broken pump and was green, a total wreck. I started with muriatic acid and it didn't seem to do a thing. I know that it will etch the walls and maybe thats what I need to kill this stuff. But I decided to try liquid Chlorine, it just washed the discoloration right away so I used that instead of the Acid. Thanks for the input.

As far as the cause. I want to blame it on the day we got into the pool straight from the ocean. It did happen right after that and in the 15 years I have had this house, I have never had black algae before and to the best of my memory, have never had a large group over straight from the beach to my pool. But... I have a concrete deck around the pool and I have noticed it has places that look like black algae or mold I am guessing from run off from my roof. Anybody understand how this stuff starts to begin with?

I only mentioned the acid wash in case you had any metal staining which chlorine wont touch

[Teapot]

Although its called black algae, it is actually a dark coloured bacteria. (Cyanobacteria) It is highly resistant to chlorine at normal levels but if you can use neat pool strength you'll certainly hurt it but it can adapt which is why chlorine dioxide is needed as that is lipid soluble so will get inside the bacterium cells and kill it.

[rfoster143X]

Although its called black algae, it is actually a dark coloured bacteria. (Cyanobacteria) It is highly resistant to chlorine at normal levels but if you can use neat pool strength you'll certainly hurt it but it can adapt which is why chlorine dioxide is needed as that is lipid soluble so will get inside the bacterium cells and kill it.

Thanks for the info. I haven't had a chance to look up chlorine dioxide but will soon.