FC loss is stumpimg me...

johnd13

LifeTime Supporter
Jun 23, 2009
67
Ok, it's been really hot and humid here... 95 to 100 degrees and high heat index the past week. My pool is not screened and gets about 10 hours of full sun a day right now. My pool temp was 90 yesterday afternoon, like bathwater.....

I have seen a loss of 7 in my FC during the day (i turned off my SWG during the day to see what the loss actually was). I do the overnight loss test and no loss and no CC. My numbers:

FC 9.0
CC 0.0
TC 9.0
TA 90 (been getting it down)
pH 7.2 (again, adding MA and aerating to get TA down)
CYA 50
CH 300

After confirming no overnight loss, I just added 5 lbs of stabilizer to raise the CYA.

I am running my SWG at almost 60% just to keep my FC in a safe range.

Can the sun knock my FC down by 7 during a hot summer day with my CYA at 50?
 

JohnT

Admin
Mod Squad
TFP Expert
Apr 4, 2007
9,536
SW Indiana
Chlorine loss due to the sun is proportional to chlorine level. Do you lose all the chlorine when running at normal levels (3-4ppm)?

The CYA test is pretty subjective, so the accuracy isn't great
 

JasonLion

TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
37,880
Silver Spring, MD
High water temperatures and extra sunlight in the early/mid summer will use up way more chlorine each day than colder water temperatures and spring/fall levels of sunlight.

Also, with a SWG you want CYA around 70 to 80, which will also help reduce chlorine loss significantly.
 

johnd13

LifeTime Supporter
Jun 23, 2009
67
JohnT said:
Chlorine loss due to the sun is proportional to chlorine level. Do you lose all the chlorine when running at normal levels (3-4ppm)?

I try and keep my chlorine level at 5. I am a little apprehensive about starting off the day at 3-4 and seeing if I lose it all...

The CYA test is pretty subjective, so the accuracy isn't great
Believe me, if I could find a way to have my CYA read for me I would. I read it three times and was right around 50 each time....
 

johnd13

LifeTime Supporter
Jun 23, 2009
67
JasonLion said:
High water temperatures and extra sunlight in the early/mid summer will use up way more chlorine each day than colder water temperatures and spring/fall levels of sunlight.

Also, with a SWG you want CYA around 70 to 80, which will also help reduce chlorine loss significantly.
CYA on its way up to 75 now according the the Pool Calculator after I added the stabilizer. I delayed raising the CYA until I confirmed no overnight loss to cut back on the chlorine needed in case I had to shock it. I'll keep an eye on it as the CYA rises and see if my daily FC loss goes down
 

ajones02

Platinum Supporter
LifeTime Supporter
Feb 4, 2010
118
Keller, Texas
johnd13, i seem to have had a similar issue. for some reason i had some CYA disappear and still do not know why. i added some stabilizer back last week to get it back up to 80. i currently have my SWG set at 75% just to keep up with the chlorine loss on a daily basis and to keep the chlorine at the 6 ppm target. same here with full sun all day long. zero shade.