Huge FC loss in one day???

[LynnDi]

Is it possible to lose 18.5 ppm FC in one day??? It was really hot and my pool gets full sun almost all day long, but still that seems like a lot.

Here are the details:

6/11/17 - opening day (evening)
Salt: 1800 ppm
pH: 7.2
FC: .5 - after 2 gallons bleach: 27.5
CC: .5 - after 2 gallons bleach: 0
TA: 50
CYA: 40
CH: 25

6/12/17 - morning OCLT
FC: 27
CC: 0

6/12/17 - evening
FC: 8.5
CC: 0

 

[jblizzle]

Yes it is absolutely possible to lose that much FC in a day.
The higher you raise the FC above the target range for your CYA, the more ppm of FC you will lose to the sun.

What does the water look like?

 

[YippeeSkippy]

Did anyone pee in the pool?? If your free chlorine oxidized it it would certainly consume said FC.

The lack of CCs may be odd, but wouldn't that be if the FC hadn't yet taken care of it? yeah, that's my story and I'm sticking to it.

Maddie

 

[LynnDi]

Water is crystal clear - I followed the TFP closing instructions at the end of the season last year so I was pleasantly surprised to open to a crystal clear pool! The only issue we had was that a bunch of dirt (I think from the cover) fell to the bottom. It took a little while to vacuum everything out but I tested after that and then added 2 gallons bleach, I wanted to bring it up to shock level just to be safe. I only lost .5 overnight and CC was at 0 so I figured it was safe to swim. I was just shocked when I saw at the end of that day it had dropped sooooo much!! I thought something might be in the pool - but CC was still 0. Also, I didn't have my SWG running and I know my stabilizer was really low. Now that the salt is dissolved the SWG is running and the CYA is currently brewing in a sock in the skimmer FC was at a 5 today and the pH was good so I let my kids go for a swim. I'm still amazed - when I was a kid it usually took about two weeks of staring at an open pool that was green and nasty before I was allowed to swim - this only took 2 days!!! I LOVE TFP!!