Pool constantly flipping to green within 2-3 days. I’m at a loss.

[Busch09]

Hi, our pool is constantly turning green. I have the impression if I turn around and don’t look at it for an hour, it turning green.
The plaster pool is about 25,000 gallons, I have a new pentair variable speed pump, a sand filter and a WaterGuru chlorine and ph device. Sat, cya and alkalinity are balanced as per WaterGuru.

The sand filter and the sand are old. The black housing might be 20, 30 years old and the sand itself is 12 years old.

The pump runs from midnight to noon daily, eight hours at 1500 PM two hours at 2500, 2 hours at 3000.

I have slammed the pool multiple times for multiple days, taking chlorine above at least 10 ppm and pH was at 7.5 when I started.
I turns clear alright, then 3 days later with chlorine at 5 and ph at 7.5 it turns green again.

I tried to read up on replacing the sand, but kind of got mixed info here on the forum wether sand needs to be replaced.

Happy to answer any additional questions and would really appreciate any help to get a grip on this.

 

[JohnT]

Welcome to TFP!

Algae is always caused by chlorine level too low for CYA level.

 

[PoolStored]

Water guru is nice for ease of use, but is not accurate enough to maintain an algae free pool.

I would get a recommended test kit. Link-->Test Kits Compared

You need the test kit to properly slam. Maintaining an FC above 10 is not sufficient. Re-read the slam process and follow it when you get your kit. Link-->SLAM Process

When you complete the slam, you need to maintain your FC for your CYA. Link-->FC/CYA Levels

 

[JJ_Tex]

and a WaterGuru chlorine and ph device. Sat, cya and alkalinity are balanced as per WaterGuru.

Can you post up your actual values, specifically your CYA and FC?

I suspect you are keeping your chlorine too low and your "SLAMs" are just knocking the algae back but not killing it all, which is why it comes back so easily when you lower your FC.

 

[Busch09]

Thank you for prompt reply’s! ok will get the test kit, slam again and report back.

 

[NicoleIvy2004]

@Busch09 So, how did it go?

 

[aggie.band.79]

My sand is older than yours!

 

[Busch09]

Ok I got the TF-100 kit. Shipping took a while.

Yesterday CyA was 57 per waterguru and ~60 per tf-100. Ph was 7.4, Alkalinity ~50.
Per pool math I added 3.5 gallons of liquid chlorine 12.5% yesterday evening.
This morning ~12h later, I did the FAS DPD test and it came in around 55 drops of R-0871, so I take that’s 27 ppm of FC.
Then I added 5 drops of R-0003 and the pool water in the cylinder stayed clear.

So does that mean my CC is 0? I searched the forum and CC 0 seems to be ok. What I am looking for is OCLT, right?

What do I do now?
Do I wait until ppm is below 22 and then add more chlorine and watch oclt?

 

[PoolStored]

Cc is 0. That’s good.

Do the oclt tonight. Whatever the fc is…

 

[Busch09]

So this morning FC is higher at 30 ppm. Can that be? It rained overnight. I didnt add any chlorine after the initial 3 gallons.

 

[NicoleIvy2004]

I'm unsure how your FC could possibly increase, so possibly that was human error with the test?
Are you cleaning your filter often during this process?
I can't believe you're still trying to get your pool water clear after all this time. Something is wrong.

 

[PoolStored]

So this morning FC is higher at 30 ppm. Can that be? It rained overnight. I didnt add any chlorine after the initial 3 gallons.

Likely testing error. Read through this:

Water Testing Errors - Further Reading

www.troublefreepool.com

 

[Busch09]

So I started the SLAM with the TF-100 Kit on Sunday Nov 10, 3 days ago. Measured FAS DPD 4 times now and FC stays at 55-60 drops, so 27-30 ppm FC. Filter running 24 hours. Backwash and scrubbing once a day.

I can't believe you're still trying to get your pool water clear after all this time. Something is wrong.
>> as the topic says I have done the slam multiple times over the last year and pool constantly turns green.

 

[SJPoe]

Can you test your fill water if any ?

If your FC is truly at 27+, and your CYA at 60, then its not algae, or it would be getting better. A picture of the pool would be useful.
How do you normally Chlorinate ?

 

[NicoleIvy2004]

Are you collecting your water sample from about arm length depth? Hold the container upside-down, put under water, then tilt to collect. Don't collect water from the surface. Test everything else you can with your TF-100 as well.

Do you see an improvement since you started the SLAM with TF-100 3 days ago?

Are you positive you're following the directions that came with the kit? It should come with a laminated sheet with step-by-step instructions that are very easy to follow, BUT also easy to get distracted and lose count of drops or get poorly formed drops. Please ask anyone with you to give you at least 10 minutes of silence so you can focus.

 

[Busch09]

I use waterguru and liquid chlorine 12.5% from leslie’s.
Pool is getting better today I guess. Water is turning grey.

 

[reggiehammond]

Please don't report Waterguru results in poolmath or in your thread here. It's too confusing. We only want to know the results from your recommended test kit.

 

[NicoleIvy2004]

• Only use the TF-100 kit you bought.
• Ask Leslie's again to confirm their bleach percentage. My liquid chlorine from Pinch-A-Penny is 10.5%.
• Have you read Pool School? Seriously, get in a comfy spot that lets you focus and read it. It's really sounding like human error at this point.

 

[NicoleIvy2004]

Pool is getting better today I guess. Water is turning grey.

Post today's picture of the pool!

 

[SJPoe]

I highly recommend taking a picture every day - sometimes you don't realize how much it's getting better until you see them all together.