How can I have algae when maintaining at 7ppm

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Loss during the daytime is very subjective to the amount of sunlight that hits the pool. Which is why we do the overnight test because the giant variable of the sun is out of the picture.

Either way based on maintaining 25 overnight it looks like you've passed the overnight test at least.
 
I recall your question to this issue a while back as noted here: SLAM - the math AND the reality. So when the FC is exceptionally high, the OCLT can be a bit more trickier.

But to answer your main question about above FC loss when the SWG is off ...... it's hard to pinpoint. Much depends on the amount of sunlight, junk that might blow in the pool, etc. Once a SLAM is completed, the FC should drop much faster (initially) from that elevated SLAM level as it tries to get back to its ideal target range. As an example, your post SLAM day 1 FC drop might be 6-8 ppm, then day 2 only 4-6, etc until the FC gets closer to its normal range where it should lose no more than 4 ppm in 24 hrs. But again, even in that example, it's hard for us to know for sure based on varying local factors that could impact FC loss.

Maybe someone else who is better at crunching numbers will have another thought or two to help.
 
Texas Splash said:
I recall your question to this issue a while back as noted here: SLAM - the math AND the reality. So when the FC is exceptionally high, the OCLT can be a bit more trickier.

But to answer your main question about above FC loss when the SWG is off ...... it's hard to pinpoint. Much depends on the amount of sunlight, junk that might blow in the pool, etc. Once a SLAM is completed, the FC should drop much faster (initially) from that elevated SLAM level as it tries to get back to its ideal target range. As an example, your post SLAM day 1 FC drop might be 6-8 ppm, then day 2 only 4-6, etc until the FC gets closer to its normal range where it should lose no more than 4 ppm in 24 hrs. But again, even in that example, it's hard for us to know for sure based on varying local factors that could impact FC loss.

Maybe someone else who is better at crunching numbers will have another thought or two to help.
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Ok, I am going out of town in a couple of hours, for 5 days.

I am just trying to figure out what to raise it to, so that it does not go so low as to allow algae to grow back, but not so high as it takes ages to drop down to a swim level after I get back.

Do you think the 'best' option to to perhaps put SWG back on, drop to half normal FC output then I will have a mixure of a controlled drop, but unlikely to drop below 7 FC in 5 days?
 
Pat, you are right, the high the FC the more you will lose to each day until it gets down to the normal range.

Since the OP is going away for 5 days, I say turn on the SWG at half the amount that was used if the FC is still near SLAM levels. If the FC is under the SLAM level then leave the SWG on at the rate it was on before the SLAM. If the FC stays high it is no big deal, you don't want to fall below the minimum amount of FC required after spending all that time and money getting this pool cleared.
 
kellyfair said:
I’m lost. What FC measurement uncertainty?
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A FC=30 could be measured anywhere between 27-33. When slamming at those levels the overnight chlorine loss can be monitored as a general guide for trends but one can get false passes and false failures due to measurement error so the final decision needs to be confirmed with an OCLT done at a much lower level.

From Pool School on the FAS-DPD test:
  • The precision of the measurement is plus or minus one drop when up to 10 drops of titrant are used, or plus or minus 10% of the final reading, when more than 10 drops of titrant are used.
 
Thanks, Poolzzz... got it now. For some reason my brain wasn’t computing what the others were saying!
 
bobandsherry said:
Do you have any water features in your pool? Descents, fountains, bubblers, etc?
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I have a round tub connected to pool that is designed to overflow into the pool and does create some bubbles

- - - Updated - - -

Ok, so just got back and tested.

12th June 6pm was FC25
17th June 10am FC 15

So lost 10 in 5 days with SWG on half normal setting

Sounds about right ?

Will do another overnight tonight.

I also bought new brush, vacuum and leaf net , and will throw old stuff away.
 

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What FC does your SWCG generate each day? It needs to add what you lose. So most likely 4 ppm or so.
 
1.30 pm 19th June

FC - 11

Just realized I have had SWG at 50% this whole time.
Lost FC 1 since 6pm last night , so a slight adjustment up should keep it level
Just did full test:
FC 11
CYA 60
TA 70
PH 7.5

Have a hardness testing issue, will post elsewhere.
 
OK, so 9pm last night , FC was 12.5 so it GAINED 1.5 from my 1.30 pm reading.
This morning at 7.30am it was at 11 again, so it lost 1.5 overnight .
However, I did not test until over an hour after sunrise, could that account for failing by .5 or does it mean I should SLAM again.

Seems odd, because I am not losing FC during the day like I did when I had algae.

thx
 

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