FC loss in hot pool

CoveredPool

Member
Aug 19, 2021
9
Chicago
Overnight, in a covered pool with 90 degree water, how much FC loss should one experience? Assume the pool is "clean" (no algae, etc) and chemistry is otherwise ideal?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,982
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
None. Or at least less than 1 ppm FC.
 

cowboycasey

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LifeTime Supporter
TFP Guide
Jul 3, 2013
8,647
Southern OK
Pool Size
15000
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Vinyl
Chlorine
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SWG Type
CircuPool SJ-40
Every pool is different, do an Overnight Chlorine Loss Test to see what your pool is losing... When it comes down to it unless something is growing you should loose very little or no chlorine overnight... My pool when covered with a solar panel goes down to using about 1 FC in 24 hours "or so"
 

CoveredPool

Member
Aug 19, 2021
9
Chicago
Every pool is different, do an Overnight Chlorine Loss Test to see what your pool is losing... When it comes down to it unless something is growing you should loose very little or no chlorine overnight... My pool when covered with a solar panel goes down to using about 1 FC in 24 hours "or so"
I have been slamming my pool every night for two weeks now. Every night, I take FC to 10ppm (my CYA is ~25). The next morning, FCF is ~5ppm.

The filter runs 24/7. The water is crystal clear and there is no visible algae or sliminess on the walls.

FC 5 (this was 10 last night when I shocked it)
PH 7.6
TA 90
CYA ~25 (this was >40 a few weeks ago)
Temperature 88 degrees
 

Kevinr14

Silver Supporter
Mar 8, 2021
294
Chandler, AZ
Pool Size
15000
Surface
Plaster
Chlorine
Liquid Chlorine
I have been slamming my pool every night for two weeks now. Every night, I take FC to 10ppm (my CYA is ~25). The next morning, FCF is ~5ppm.

The filter runs 24/7. The water is crystal clear and there is no visible algae or sliminess on the walls.

FC 5 (this was 10 last night when I shocked it)
PH 7.6
TA 90
CYA ~25 (this was >40 a few weeks ago)
Temperature 88 degrees

Round the CYA to 30 and your FC SLAM target is 12ppm. You say you're slamming at night...Are you testing throughout the day to ensure your FC is at target? If not, you're not actually performing the SLAM Process
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
28,491
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
I have been slamming my pool every night for two weeks now. Every night, I take FC to 10ppm (my CYA is ~25). The next morning, FCF is ~5ppm.

Please READ the SLAM Process

Follow it STEP by STEP with no shortcuts.

The M in SLAM means MAINTAIN.

You must maintain your SLAM FC level of 12. Every time you test and your FC is below 12 you MUST raise it to 12 or above. The more often you test and maintain the faster the process will go.

What you were doing was killing algae early in the night and then letting it grow back during the day. You will never win the battle that way.
 

CoveredPool

Member
Aug 19, 2021
9
Chicago
Please READ the SLAM Process

Follow it STEP by STEP with no shortcuts.

The M in SLAM means MAINTAIN.

You must maintain your SLAM FC level of 12. Every time you test and your FC is below 12 you MUST raise it to 12 or above. The more often you test and maintain the faster the process will go.

What you were doing was killing algae early in the night and then letting it grow back during the day. You will never win the battle that way.
The pool has an auto cover. It is completely dark all day. How is algae growing?

The water is completely clear, and there are no signs of algae on the walls (no sliminess, etc).
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,982
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Then there should be no FC loss.
 

jesper

Gold Supporter
Silver Supporter
Mar 10, 2019
99
Cyprus
Pool Size
34000
Surface
Plaster
Chlorine
Salt Water Generator
The pool has an auto cover. It is completely dark all day. How is algae growing?

The water is completely clear, and there are no signs of algae on the walls (no sliminess, etc).

my auto cover doesn’t completely block all light, my pool is also covered all the time we’re not using it, yet I still managed to get algae last year when the temperature and pool usage went up, and I didn’t adjust the SWG quickly enough to compensate for increased chlorine usage.

this year I run the FC a bit higher and have had no issues, and the water is even cleaner
 
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ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
28,491
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
The water is completely clear, and there are no signs of algae on the walls (no sliminess, etc).

You can have algae brewing in clear water. You just have not gotten a full green algae bloom yet. But it is lurking there just waiting for your FC level to drop and it will be off to the races.

If you have FC loss at night, and in a covered pool, it is only from one reason - algae. Unless you have been tossing in pool store potions or algaecides that contain chemicals like ammonia that consume chlorine.
 

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CoveredPool

Member
Aug 19, 2021
9
Chicago
You can have algae brewing in clear water. You just have not gotten a full green algae bloom yet. But it is lurking there just waiting for your FC level to drop and it will be off to the races.

If you have FC loss at night, and in a covered pool, it is only from one reason - algae. Unless you have been tossing in pool store potions or algaecides that contain chemicals like ammonia that consume chlorine.
No, no other chemicals are going into the pool.

What about bacteria? Since I was experiencing rapid CYA loss, this article (poolsolutions.com...) led me to believe it was an issue of CYA-eating bacteria.

In any case, I will take your advise and maintain slam-level FC throughout the day too. Hopefully that works...
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
28,491
Northern NJ
Pool Size
35000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
What about bacteria? Since I was experiencing rapid CYA loss, this article (poolsolutions.com...) led me to believe it was an issue of CYA-eating bacteria.

If you had that CYA would go to zero and so would your FC. You would not be able to hold any chlorine in the water.
 
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CoveredPool

Member
Aug 19, 2021
9
Chicago
You can have algae brewing in clear water. You just have not gotten a full green algae bloom yet. But it is lurking there just waiting for your FC level to drop and it will be off to the races.

If you have FC loss at night, and in a covered pool, it is only from one reason - algae. Unless you have been tossing in pool store potions or algaecides that contain chemicals like ammonia that consume chlorine.
How many days should slamming take - for a pool with no visible algae?
 

PoolStored

Gold Supporter
Jun 24, 2021
547
Ashtabula, OH
Pool Size
31000
Surface
Vinyl
Chlorine
Liquid Chlorine
How many days should slamming take - for a pool with no visible algae?
There are lots of variables. The biggest ones you can control:
a) If you can check your FC and replace chlorine to get back to SLAM FC level every 2 hours. It will go quicker.
b) If you scrub/scrub/scrub everything, often, it will go quicker. Behind the lights, inside any ladders, around all water features, the float for your autofill, your skimmers. DON'T MISS ANYTHING. I didn't think of the hollow tubes in my ladder. It made what could have been a 2 day slam into a 5 day slam.