We just opened our 24ft round above ground pool. We can not keep chlorine levels at a normal number. Water is crystal clear and ther is no visible algea in pool. Tested water last night at 9:00pm number were FC-2,Ph-7.5, Alk-125-130 Cal-150 and CYA 25-30. Tested again this morning and numbers were FC-0,Ph-7.5,Alk-130,Cal-150 and CYA-25-30. We use a Hayward S-166T high rate sand filter. The pool holds about 13500 gallons of water. I know that it is four feet deep with a vinyl liner. Can you tell me why chlorine levels are changing over night ?
Can't keep chlorine in pool
- Thread starter missmiller
- Start date
Welcome to TFP!
You probably have some ammonia, or other invisible organic debris, in the water. You need to shock the pool until you can hold a consistent FC level overnight. See this article.
You probably have some ammonia, or other invisible organic debris, in the water. You need to shock the pool until you can hold a consistent FC level overnight. See this article.
How long after I shock it should I wait to test? Should I use shock or bleach? If so how many gallons of bleach?
Welcome to TFP. 
Can you create a signature with all your pool and equipment info.
Go to User Control Panel, then Profile, then Edit Signature. This would be very helpful for those of us answering your questions.
Can you create a signature with all your pool and equipment info.
Go to User Control Panel, then Profile, then Edit Signature. This would be very helpful for those of us answering your questions.
I shocked the pool again yesterday morning at 7:00am and checkes it at 2:30pm FC_10,Ph-7.5,Alk-120, Cal-150 and CYA was 30. Tested at 7:00am this morning FC-10,Ph-7.5,Alk-120,Cal-150 and CYA- was 30. Tested again at 2:00pm and FC-10 everything else stayed the same. It has been raining most of the day. Could this be why the FC fell 5 ppm?
Sometimes, when you open in the spring, there can be a little ammonia in the pool. Until you add enough chlorine to break down the ammonia, the chlorine will just "vanish". Once the ammonia is gone, everything goes back to normal.
If I am reading your test results correctly, FC has been 10 for the last 24 hours or so. If that is right then you should be fine now.
missmiller said:
If you are holding chlorine overnight...there is no reason to "shock"...
If there are no CC...there is no reason to "shock"
If there is no algae in your pool....there is no reason to "shock"
If your water is clear...there is no reason to "shock"
From my reading of your post...your chlorine held overnight...you should be good
Ah, still not a problem. FC is expected to fall during the day. Sunlight consumes chlorine, even on cloudy days.
For reference...I use consistently about 3 to 4 ppm chlorine/day with CYA at 40....no cover, full sun...considering going to 50 ppm CYA in July to see what that does...