Min time for OCLT


LifeTime Supporter
Jul 12, 2008
Seacoast, NH
Is there a min period of time for the OCLT? I tried to do the test last night. I set my alarm for 5 am, which is dawn,and woke up with no memory of my alarm having gone off at all. I did the test then and FC had dropped 3.5.

I kept the pool at shock level today and took a sample at 9:30 pm. I'm going to try to get up at 5 to try again, but I am not hopeful. DH has narcolepsy and I have sleep apnea, so walking up is not our strong suit. If I test now (3.5 hours after the starting point) will any useful information be gained.


TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
If you lose FC in 3.5 hours without sunlight on it, it will tell you that you'll lose a lot more before sunrise.

If you don't lose anything, it doesn't mean that you won't lose anything before the sun hits the water, only that it's not enough to measure yet.

PS: If you lost a bunch of FC, you can get a jump start on the shock process by dumping the bleach in tonight, so it has several hours to work on the algae before the sun starts degrading it.


LifeTime Supporter
Jun 17, 2010
Glendale, CA
The point of the test is to eliminate sunlight as one potential source of chlorine loss. If your pool has only received a couple hours of early morning sun - that is not going to throw the test way off. Put another way - testing at 6.30am should yield a valid result. If it was later in the day (full sun) it will throw the test off by some unknown amount.

It sounds like you did the test in the morning and had lost 3.5ppm (which is a lot) - so you still need to shock.

I wouldn't stress too much setting an alarm for the morning. Keep shocking and testing - at some point you will see your overnight chlorine loss drop off.


TFP Expert
LifeTime Supporter
Jul 30, 2010
Twin Cities, MN
lightningguy brings up a good point, so if the sun hadn't spent much time on the pool before you did your test yesterday, then you definitely need to shock.

Post your 3.5 hour test, if you are still awake.