Strange smell and algae growth despite perfect chemistry/maintenance

Pool94

Member
Apr 9, 2022
15
North Carolina
Pool Size
26000
Surface
Vinyl
My pool has developed a strange odor over the past few weeks and is slightly cloudy with small amounts of algae quickly growing on the bottom of the pool every day requiring constant scrubbing. The pool has a slight haze but is still relatively clear and doesn't seem bad enough to warrant undergoing a SLAM.

It seems every time I complete a SLAM my water is perfect for several days (perfectly clear, no overnight FC loss, CC < 0.5) but then starts to slowly degrade when I lower the FC from shock to target levels. I keep my FC well above the target level for my CYA. I would keep my FC even higher but don't feel comfortable swimming in a pool with FC > 15ppm where the CYA is around 30-40.

Any thoughts? Are there any other factors that could be responsible for the smell and persistent algae growth?

Here's my current chemistry:

FC: 8
CC: 0.5
pH: 7.3
TA: 70
CH: 225
CYA: ~30 - 40
 

YippeeSkippy

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Jan 17, 2012
19,642
Evans, Georgia
Whose swimming in the pool? Lots of kids? I'm always suspicious of kids assuming at least one will pee in the pool which would use up some FC.
Also how often are you testing your water once the SLAM process is over??

Maddie :flower:
 

Pool94

Member
Apr 9, 2022
15
North Carolina
Pool Size
26000
Surface
Vinyl
You likely, and potentially unknowingly, allowed your FC to drop below minimums at some point.

How old are your reagents?
My reagents are new (under 4 months old). I recently received another R-0871 and tests remained consistent. I have also cross checked with other pool stores occasionally and the results always match up.

I test FC pretty much every day and my results are always at the target FC or above.
 

Pool94

Member
Apr 9, 2022
15
North Carolina
Pool Size
26000
Surface
Vinyl
Whose swimming in the pool? Lots of kids? I'm always suspicious of kids assuming at least one will pee in the pool which would use up some FC.
Also how often are you testing your water once the SLAM process is over??

Maddie :flower:
Only me and my partner swim in the pool - usually only 3-4 times a week.
I test my FC almost every day to ensure it never drops below target levels.
 

PoolStored

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Do you use pool math? Can you share your logs? Login to PoolMath, if you have it, with your ID/password from the forum, go to home screen, then to the gear in the upper left corner, scroll down to bottom and enable sharing with TFP. Might help us...

What is your target for FC?
 

Pool94

Member
Apr 9, 2022
15
North Carolina
Pool Size
26000
Surface
Vinyl
Do you use pool math? Can you share your logs? Login to PoolMath, if you have it, with your ID/password from the forum, go to home screen, then to the gear in the upper left corner, scroll down to bottom and enable sharing with TFP. Might help us...

What is your target for FC?
I do, but I don't always record in tool directly.
My CYA hovers between 30-40, so I take the higher value and set my target to 7ppm. But most of the time I am above that target. I can't remember a time recently where I got close to the minimum.
It's almost like I am having to keep my FC 5-6ppm higher than the recommended target value to have good results, however, this puts me close to the SLAM FC value, which some say can be unsafe to swim in.
Even during my experience with SLAM when I had a green pool - I was not successful through SLAMing at 16ppm. I had to SLAM above 20ppm to get results.
 

reggiehammond

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Oct 4, 2020
706
Fort Worth, Texas
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Your comment seems to indicate you’ve slam’d more than once. Not to read into it too much, but perhaps you have algae and have never gotten rid of it completely?

There’s threads every day here regarding slam processes that are taking a long time or not solving the issue, and almost always there’s a hidden colony of algae.
 

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Pool94

Member
Apr 9, 2022
15
North Carolina
Pool Size
26000
Surface
Vinyl
Your comment seems to indicate you’ve slam’d more than once. Not to read into it too much, but perhaps you have algae and have never gotten rid of it completely?

There’s threads every day here regarding slam processes that are taking a long time or not solving the issue, and almost always there’s a hidden colony of algae.
I have had to SLAM more than once. However, I only let my FC levels fall to target after passing all 3 criteria of the SLAM (clear pool, CC ≤ 0.5ppm, no overnight FC loss). I followed the exact steps and my pool water afterwards looked immaculate for 1-2 weeks, but then started to degrade despite having perfect chemistry/maintenance. My experience is I am having to keep my target FC *much* higher than what TFP says to prevent algae from slowly taking over.
 

PoolStored

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I do, but I don't always record in tool directly.
My CYA hovers between 30-40, so I take the higher value and set my target to 7ppm. But most of the time I am above that target. I can't remember a time recently where I got close to the minimum.
It's almost like I am having to keep my FC 5-6ppm higher than the recommended target value to have good results, however, this puts me close to the SLAM FC value, which some say can be unsafe to swim in.
Even during my experience with SLAM when I had a green pool - I was not successful through SLAMing at 16ppm. I had to SLAM above 20ppm to get results.
GREAT! Can you share your logs? Will really help us.

How old are your reagents?

When was the last time you checked your CYA? Did you do the test outside, with bright sunlight at your back, holding it at your waist in the shadow of your body?
 

Pool94

Member
Apr 9, 2022
15
North Carolina
Pool Size
26000
Surface
Vinyl
GREAT! Can you share your logs? Will really help us.

How old are your reagents?

When was the last time you checked your CYA? Did you do the test outside, with bright sunlight at your back, holding it at your waist in the shadow of your body?
You should be able to see my logs now.
I purchased my TF-Pro test kit with all reagents back in early April.
CYA was checked a few days ago and I read it as ~35. I test in my garage underneath a work lamp. My CYA tests have matched up closely to Leslie's in the past.
 

PoolStored

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You should be able to see my logs now.
I purchased my TF-Pro test kit with all reagents back in early April.
CYA was checked a few days ago and I read it as ~35. I test in my garage underneath a work lamp. My CYA tests have matched up closely to Leslie's in the past.
Nope, no logs. Are you signed into Pool Math with the same ID/PW as the forum?

Great!!

Imma guess your CYA level is higher than you think. CYA test is highly susceptible to lighting conditions.

From the article: The test is designed to be performed in bright sunlight and will read low if you use indoor lighting.


That is why you needed higher SLAM and why you are getting algae...your target FC is likely too low for your ACTUAL CYA level.

Hope that helps!!!
 

Pool94

Member
Apr 9, 2022
15
North Carolina
Pool Size
26000
Surface
Vinyl
Nope, no logs. Are you signed into Pool Math with the same ID/PW as the forum?

Great!!

Imma guess your CYA level is higher than you think. CYA test is highly susceptible to lighting conditions.

From the article: The test is designed to be performed in bright sunlight and will read low if you use indoor lighting.


That is why you needed higher SLAM and why you are getting algae...

Hope that helps!!!
You may need to refresh your browser. I opened an incognito window and went to my profile and was able to see the logs.
So it isn't possible to reliably test CYA outside of natural/bright daylight?
Even with a margin of error of +-10 it wouldn't fully explain my scenario. I have gotten tests done at Leslie's multiple times and my recorded CYA reading was usually with +-5 of their reading. Maybe they are testing low too?
 

PoolStored

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You may need to refresh your browser. I opened an incognito window and went to my profile and was able to see the logs.
So it isn't possible to reliably test CYA outside of natural/bright daylight?
Even with a margin of error of +-10 it wouldn't fully explain my scenario. I have gotten tests done at Leslie's multiple times and my recorded CYA reading was usually with +-5 of their reading. Maybe they are testing low too?
I actually called Taylor Technologies and asked them how they standardized their test. They recommended the strong indirect lighting and the sun to one's back. I have since compared the CYA test to CYA Standard solution and found that technique gave the most accurate result for that standard. Using the standard was one of the BEST things I did to get the "CYA Eye."

I don't even test CYA on a cloudy day. It is very, very rare for indoor lighting in a home to be as bright as outdoor indirect light.

Very roughly speaking, direct overhead sunlight is around 100,000 lux, strong indirect light (i.e. shaded from the sun) is around 10,000 lux, an overcast sky is around 1000-5000 lux but varies on how overcast, indoors is usually < 1000 even in a bright kitchen (more typically 500 lux).

Don't get me started on Leslie's, as a TFP guide, I would have to remove it after I wrote it.
 

PoolStored

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Got the logs on iPhone.

You have consistently hit an FC of 5 right before the last 2 SLAMS. You also hit 3.5 before the Slam before that.

I think you may have the confluence of two things going on:
1) Your CYA is higher than you think.
2) Other testing error making you think your FC is higher than reality.

Are you allowing the drops to fall from the reagent bottles on their own, really slowly? Like squeeze the bottle very lightly and allow the drops to form on their own? Like Drop, one one thousand, drop. If not and you are rapidly squeezing them out, the drops will be smaller, giving you higher results (FC).

Do you have a smart stir? My brother, who owned a pool for 30 years came to visit. We did back to back comparison, me with smart stir, him swirling. His results were 1ppm higher. Smart stir makes the mixing of chemicals consistent.

It is safe to swim up to SLAM level. I keep my pool 1-2 ppm above target just to avoid this situation. Nobody will ever know our secret.
 

duraleigh

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I have no answers for you except to remind you that your chemistry is NOT perfect or you wouldn't have organics growing (and smelling) in your pool.

SLAMing the pool correctly results in a sanitized pool that is algae (and smell) free. Maintaining your chemistry at the levels we suggest keeps it that way.

There is no miracle algae (or organics) that can survive a correct SLAM so don't waste your time looking for some other, exotic cause.

Reread the SLAM procedures..........there is an error(s) somewhere in your methods.
 

Pool94

Member
Apr 9, 2022
15
North Carolina
Pool Size
26000
Surface
Vinyl
Got the logs on iPhone.

You have consistently hit an FC of 5 right before the last 2 SLAMS. You also hit 3.5 before the Slam before that.

I think you may have the confluence of two things going on:
1) Your CYA is higher than you think.
2) Other testing error making you think your FC is higher than reality.

Are you allowing the drops to fall from the reagent bottles on their own, really slowly? Like squeeze the bottle very lightly and allow the drops to form on their own? Like Drop, one one thousand, drop. If not and you are rapidly squeezing them out, the drops will be smaller, giving you higher results (FC).

Do you have a smart stir? My brother, who owned a pool for 30 years came to visit. We did back to back comparison, me with smart stir, him swirling. His results were 1ppm higher. Smart stir makes the mixing of chemicals consistent.

It is safe to swim up to SLAM level. I keep my pool 1-2 ppm above target just to avoid this situation. Nobody will ever know our secret.
I do use a smart stir, but I may have been squeezing the drops out too quickly. I'll be more careful to go slower. Between that and getting an artificially low reading on my CYA may indeed be the culprit.
I'll implement your suggestions and aim to maintain my FC a little over target recommendations. Thanks!
 

PoolStored

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Jun 24, 2021
2,794
Ashtabula, OH
Pool Size
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Surface
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Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
I do use a smart stir, but I may have been squeezing the drops out too quickly. I'll be more careful to go slower. Between that and getting an artificially low reading on my CYA may indeed be the culprit.
I'll implement your suggestions and aim to maintain my FC a little over target recommendations. Thanks!
Spot on Pool94!

Slam on! Hopefully for the last time.
 

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