quick question about OCLT

Pv2

LifeTime Supporter
Aug 14, 2013
1,082
south east Arizona
related to my post about fresh reagents, is the OCLT valid at maintenance chlorine levels or should it be done at shock level? in other words, does a higher chlorine level magnify any over night loss? or is <1 ppm loss at 4-5 ppm the same at 12+ ppm?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,665
Laughlin, NV
Pool Size
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Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
The FC should be, at a minimum, the target range for your CYA at the start of the OCLT. Best is to just adjust FC to about 10 ppm.

If at SLAM levels, do the OCLT at those levels. Though at SLAM levels above 20 ppm, the testing error can create an issue. If a couple OCLT's fail though the other two SLAM criteria are passing, let the FC come down to below 20 ppm and do the OCLT.
 
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2KR88

Silver Supporter
May 29, 2019
8
Central Washington
Pool Size
13500
Surface
Fiberglass
Chlorine
Liquid Chlorine
Marty,
I don't remember reading anything about an error in the OCLT when slamming above 20 ppm. Can you elaborate? I'm in my 4th day of a slam and wondering... My CYA is 55 so I was using 60, which is slam at 24. Started at 7.4 PH Water was clear from the start but I did find maybe 4 square inches total of black algae which I sanded out with 2000 grit paper. During daylight I've been testing and adding every two hours. And brushing once per day. More often than not the combined is testing at 0. Overnight numbers below. While this morning might have been a success I'm still testing and adding to make sure. Planning to do another OCLT tonight and wondering if I should let the level drift down below 20.

Thanks in advance.

First Night 8:00pm 23 ppm .5 CC
Next Morning 5:00am 19 ppm .5 CC
That Night 8:00pm 22.5 ppm .5 CC
Next Morning 5:00am 20 ppm .5 CC
That Night 9:00pm 24 ppm 0 CC
Next Morning 5:00am 20.5 ppm 0 CC
That Night 9:00pm 21 ppm .5 CC
This Morning 5:00am 20.5 ppm .5 CC
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
10,402
NY
We’ve had a few lately that lost unexpected FC overnight at the tail end of SLAM. It’s hard to explain because with no algae and no sun, whatever is in there should still be there in the morning. Maybe it evaporates with the warm water in the cooler overnight ? You’ve been vigilant in your efforts and you did GREAT. It’s fair now to let the FC drift down and see if it holds once it’s much closer to normal range.

If not you won’t lose any progress with crystal water and all you’ve done so far.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,665
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
The test has error. Essentially 1 drop in 20. So as you go above 20 ppm FC, you get into error levels that are greater than 1 ppm FC.
 
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Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
10,402
NY
@mknauss any idea as to why it only seems to affect some folks ? Is it a luck if the draw kinda thing or does the right mix of 2 other test results combine to boost the margin of error on the tests ?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,665
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Like all error, it is never consistent. That is why the FC loss overnight is 1 ppm or less. In reality, it should be zero loss if no error.
 
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Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
10,402
NY
Thanks. I guess too that 40+ drops leaves PLENTY of room for human error too. That’s a lot of times to do something exactly the same for any of us.
 
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2KR88

Silver Supporter
May 29, 2019
8
Central Washington
Pool Size
13500
Surface
Fiberglass
Chlorine
Liquid Chlorine
Reporting back...I'm sure you're all on the edge of your seats! :sleep:
I let it drift down. 18.5 at 9:00 last night, 17.5 at 5:00 this morning.

On to my next test: Closed the cover, no chlorine added, and will check again in 24 hours. Trying to get a better handle on what my consumption is with the cover closed so that I can plan for when I'm absent. I know my sig says liquid chorine. I'm just making the switch to liquid after two years with tablets chasing the CYA up and down (partial drain/refill) and not really understanding all of what I was doing or what was causing what. Behold Trouble Free Pool! Really impressive. I still have a feeder but am trying to use liquid when I'm here, and a combination of somewhat high levels when I leave and Trichlor in the feeder. Will see how it goes the rest of this season. I am considering SWG.

Thanks for all the help!!!
 
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