Overnight loss test question

yankees177

Active member
Aug 23, 2016
35
Ballston Lake, NY
It was a hot sunny day today in upstate NY. 86 and pool had sun from 10am to 6pm. Last night I took my measurement and it said 2ppm and since my my CYA is 40 (14kGallon pool) I needed to add. I put in enough chlorine to get me to 7ppm but didn't test. A full 24 hours later, after about 3-4 hours of pool time I decided to test again and I'm at 3ppm.

Since I dont know where it finished after I added chemicals last night I am assuming that's a 4ppm chlorine loss. Seems pretty hefty for one day, no?

My question is since the ONLT says greater than 3ppm can I still do a test knowing I'm right at 3ppm? Is there any issue. If I am 1 or less tomorrow then I'll test to see how good my chlorine is and rule that out. Thanks for the advice!

Edit... Decided to do a late night test so I added 29oz to get me to 5ppm so I will retest in an hour and see where I'm at for my OVNLT.
 
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Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
15,051
Bedford, TX
177,

I like your plan to rerun the test at 5 ppm..

The whole point of the OCLT is to run an accurate test right after sundown, and another accurate test just before sunup. Guessing what the FC should be is not accurate enough.. :mrgreen:

Thanks,

Jim R.
 
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jblizzle

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May 19, 2010
43,260
Tucson, AZ
Letting the FC get down to 3ppm with a CYA of 40ppm is really too low in my opinion. That is at the minimum. You should probably raise your target levels to 6-7ppm and make sure it stays above 4ppm to have some buffer. See the FC/CYA Chart
 

yankees177

Active member
Aug 23, 2016
35
Ballston Lake, NY
Letting the FC get down to 3ppm with a CYA of 40ppm is really too low in my opinion. That is at the minimum. You should probably raise your target levels to 6-7ppm and make sure it stays above 4ppm to have some buffer. See the FC/CYA Chart
The chart shows 3-7 is optimal range. I typically pump it up once it gets there to 7 and let it get to 3 and rinse repeat. If it's too low it shouldn't be the minimum, no?
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
15,051
Bedford, TX
The chart shows that the target is 5 to 7 and that is where you should be trying to run.. Not 3 to 7...

The minimum is based on everything being perfect... your tests, your CYA level, when you test, etc. In theory 3 is the minimum, but in practice it makes sense to never drop that low.

Thanks,

Jim R.
 

yankees177

Active member
Aug 23, 2016
35
Ballston Lake, NY
The chart shows that the target is 5 to 7 and that is where you should be trying to run.. Not 3 to 7...

The minimum is based on everything being perfect... your tests, your CYA level, when you test, etc. In theory 3 is the minimum, but in practice it makes sense to never drop that low.

Thanks,

Jim R.
Sounds good. I think then pool math needs to be updated because it also shows 3-7 and I go off of that. Also all my numbers are good so I'm not too worried but it could be confusing for a novice.