Black dirt like growth? Persistent but easy to disperse

Draddy

Member
Apr 11, 2019
23
Boca raton
This place had been unbelievably helpful with my weird pool.

Have a new issue, any idea what this is? Of course my first panic was black algae, but this is easy to brush away with your foot.

But it comes back every day. Pool is balanced (will post screenshot). Last night i vacuumed, brushed then vacuumed again. And today it’s back at the same quantity as before.

Any idea what this is?

Video:
 

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aeh0603

Well-known member
Apr 6, 2016
185
San Diego, CA
It looks a lot like dead algae to me. If that is the case you will need to perform a SLAM to kill the algae. How do you test your water? Can you post a full set of testing results?
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
12,574
Bedford, TX
D,

I also suspect it is algae... Why in the world is your CYA zero? An FC of 5 with a CYA of zero is very harsh feeling...

Plus, I suspect your FC of 5 burns off very quickly...

I suggest you run an Overnight Chlorine Loss Test... Overnight Chlorine Loss Test to confirm if you have algae or not..

Basically, if your FC goes down after dark and before sunrise, it has to be consumed by algae...

If you fail the OCLT then you need to perform a SLAM.. SLAM Process

Thanks,

Jim R.
 

Draddy

Member
Apr 11, 2019
23
Boca raton
Sorry, I should have added a note about the CYA. IT was zero on Monday when we closed on the house. Chlorine was 2. Added 125 of (liquid) stabilizer, and a gallon of chlorine. haven’t test again for cya (only have the 5 way). Will take another sample to the store.

Will look into the shock treatment. Thanks!


Attached is the result from the store. will take another sample to get another cya reading.
 

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Draddy

Member
Apr 11, 2019
23
Boca raton
D,

Please read our Pool School... We do not "shock" anything... We do things differently than Pool $tores...

ABCs of Pool Water Chemistry

Thanks,

Jim R.
Sorry for assuming what the S stood for. I would definitely follow the instructions from here. Thank you!

It looks a lot like dead algae to me. If that is the case you will need to perform a SLAM to kill the algae. How do you test your water? Can you post a full set of testing results?
I’m using a 5 way right now, will order a bigger kit.
 

Draddy

Member
Apr 11, 2019
23
Boca raton
Quick question about the slam method, all the kits I’m finding with “FAS-DPD chlorine test” only show readings up to 10. How do I test if I’m at the recommended 15-20?

sorry, dumb question. (Mod feel free to delete this comment)
 
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Teald024

TFP Guide
Welcome to TFP!

You are learning, no questions are dumb. Glad you found your answer.

I highly recommend getting the TF-100 test kit. Once you compare the amount of reagents provided, it is the best deal for the money. Since you likely have to perform the SLAM Process process, you will go through more FC tests than the K-2006c offers.
 
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Draddy

Member
Apr 11, 2019
23
Boca raton
Good morning all, I know my pool has too much chlorine, ignoring that for the moment.

@Jimrahbe : I did an OCLT - at 9pm last night, chlorine was at 9.8. This morning at 6:30 am, it was at 9.2. According to the link, that doesn’t constitute a failure. But should I still consider that loss significant?

I have noticed that since my last vacuum/brush/vacuum/filter clean (which I’ve done about every other day this week), there has been less black stuff at the bottom of the pool. Not none, but less. It’s still easy to disperse, so I still don’t think it’s black algae.


Any guidance for a pool newbie as to what to do next? Here’s a pretty good thread of other people with the same issue: Black dust - could be algae - on bottom of pool - Swimming Pool Help

==========================================
------------------------------------------
Build Type: Concrete
Volume: 10000 gallons
------------------------------------------
Latest Test Result Summary:
FC: 9.2 (6 minutes ago)
CC: 10.0 (20 hours ago)
pH: 7.4 (20 hours ago)
TA: 90 (2 days ago)
CH: 250 (4 days ago)
CYA: 50 (20 hours ago)
TEMPERATURE: 75° (4 days ago)
CSI: 0.05 (6 minutes ago)
==========================================
 
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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
5,964
Northern NJ
Your pool does not have too much chlorine. At CYA 50 you can have up to FC 20 and swim safely. Your tatget is 6-8 so you are just a bit high. See FC/CYA Chart

CC 10 is not right. Where is that from?

You have your own test kit yet?
 

Draddy

Member
Apr 11, 2019
23
Boca raton
Your pool does not have too much chlorine. At CYA 50 you can have up to FC 20 and swim safely. Your tatget is 6-8 so you are just a bit high. See FC/CYA Chart

CC 10 is not right. Where is that from?

You have your own test kit yet?
That’s good to know. I’ll let it burn down and keep it around 8. Previous owner put a gallon in per week, and 2 pucks in a floater. I’ve removed the floater and trying to maintain with just liquid.

Got the 5 way and the dpd this week, should have the real kit recommended above this week.

You’re totally right, that was a misstype on my part. I think i confused CC with total chlorine when entering results. I don’t have a way to test combine chlorine yet.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
5,964
Northern NJ
I would keep your FC on the high side in case you have some algae or pollen using it up.

Relax and wait until you have a test kit. Then post a full set of tests and we will see.
 
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Draddy

Member
Apr 11, 2019
23
Boca raton
Got the full tf100 kit in, see results below. Any tips based on these for getting rid of this stuff? Been brush/vac/brush/clean filtering every other day for almost 2 weeks.

I think combined chlorine was in between .5 and 1. 1 drop worked, but 2 seemed to make it slightly better.

==========================================
------------------------------------------
Build Type: Plaster
Volume: 10000 gallons
------------------------------------------
Latest Test Result Summary:
FC: 9.0 (30 minutes ago)
CC: 0.5 (30 minutes ago)
pH: 7.8 (30 minutes ago)
TA: 100 (30 minutes ago)
CH: 275 (30 minutes ago)
CYA: 40 (30 minutes ago)
BORATES: 0 (30 minutes ago)
TEMPERATURE: 75° (9 days ago)
CSI: 0.16 (30 minutes ago)
==========================================
 
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aeh0603

Well-known member
Apr 6, 2016
185
San Diego, CA
I would do a SLAM. Overall your numbers look good, but if it's algae your FC is not high enough to kill it all. Your water is still pretty clear so it should go quickly.

If you SLAM, make sure to lower your pH first since you can't test pH with the FC over 10.
 
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Draddy

Member
Apr 11, 2019
23
Boca raton
Didn’t think the PH of 7.6/7.8 would be an issue, I’ve been slamming since Friday, current FC is 21.5 (overshot the bleach). I’m still passing the OCLT, last night was 22, this morning was 21.5. Should i let the chlorine burn down, lower the ph then bring it back up?

But now the stuff is white and black.....

Thank you all for your help!
 

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Teald024

TFP Guide
Didn’t think the PH of 7.6/7.8 would be an issue, I’ve been slamming since Friday, current FC is 21.5 (overshot the bleach). I’m still passing the OCLT, last night was 22, this morning was 21.5. Should i let the chlorine burn down, lower the ph then bring it back up?

But now the stuff is white and black.....
The lower pH helps the chlorine do it’s job better. Since you’re already at high FC, I’d stay there until the water clears and you pass all 3 criteria for stopping.
Clear water includes no more black stuff on the floor.
That stuff turning white is the dead algae.
 
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dw886

Gold Supporter
Sep 19, 2016
222
ND
Just as words of encouragement, this same thing happened to me when we first got our pool. I "assumed" that the black stuff in the bottom of the pool was construction dirt that had gotten into the pool, but I didn't know any better. I was cleaning it up daily, but couldn't figure out how it was coming back. On a whim, because I had been reading on here since before construction was completed, I did a slam. Took about a week, but eventually the stuff that looked like dirt on the bottom of the pool quit forming, and my water was far clearer after I finished the process. Follow the SLAM process, and keep brushing it to stir things up.

Once you have the pool in order, stay the course with how people on this site guide you and you'll be far better off. Now I pretty much know that if I can sweep up anything on the bottom of the pool, I'm on the verge of an outbreak. The pool filters do a really good job of keeping your water clear when your pump is running. In 3 years of pool ownership, this has only happened to me when I had an issue, and a SLAM took care of it...
 
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Draddy

Member
Apr 11, 2019
23
Boca raton
Just as words of encouragement, this same thing happened to me when we first got our pool. I "assumed" that the black stuff in the bottom of the pool was construction dirt that had gotten into the pool, but I didn't know any better. I was cleaning it up daily, but couldn't figure out how it was coming back. On a whim, because I had been reading on here since before construction was completed, I did a slam. Took about a week, but eventually the stuff that looked like dirt on the bottom of the pool quit forming, and my water was far clearer after I finished the process. Follow the SLAM process, and keep brushing it to stir things up.

Once you have the pool in order, stay the course with how people on this site guide you and you'll be far better off. Now I pretty much know that if I can sweep up anything on the bottom of the pool, I'm on the verge of an outbreak. The pool filters do a really good job of keeping your water clear when your pump is running. In 3 years of pool ownership, this has only happened to me when I had an issue, and a SLAM took care of it...

That’s really helpful. Thank you! Both for knowing someone else has faught the same stuff, but also to know how long to expect it to take.



Was sweeping, and found one area that didn’t disperse easily like the rest. Any cause for concern?
 

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