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?
FC loss in hot pool
- Thread starter CoveredPool
- Start date
- May 3, 2014
- 58,345
- Pool Size
- 6000
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
- Jul 3, 2013
- 9,028
- Pool Size
- 15000
- Surface
- Vinyl
- Chlorine
- Salt Water Generator
- 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"
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
- Jul 21, 2013
- 52,407
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
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).
- May 3, 2014
- 58,345
- Pool Size
- 6000
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-40
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
- Jul 21, 2013
- 52,407
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
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...
- Jul 21, 2013
- 52,407
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
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.
- Jul 21, 2013
- 52,407
- Pool Size
- 35000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
- Jun 24, 2021
- 7,500
- Pool Size
- 30000
- Surface
- Vinyl
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-60
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.
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