How long for FC to drop from shock level to normal

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L

lizardflats

0
Jul 16, 2012
13
San Jose, CA
We just got our 16' x 48" UltraSet up and running. After 5 days of dichlor, the CYA is at 60 (about right for running the Intex SWG), the pH is 7.6, and the FC is 25 (shock level). Salt is at 2800, so I'll be adding another 13 pounds to get it up to 3200.

I'm not adding any bleach or running the SWG yet, just running the filter 2-4 hours each evening.
Outside temps are in the mid 80's and water temp is about 72-74 F in the afternoon, dropping to about 68F each morning (we have a solar bubble cover on it right now). (nice mild Indian Summer in the SF Bay Area).

The kids are hoping they can go in the pool this coming weekend.
Any idea how long it will take the chlorine level to get back down under 6?
 
It's been almost 2 weeks now since I did the initial dichlor treatment on our new 16x48" Ultraframe pool and the FC is still at 20 (it was a little over 25 when I finished the dichlor) and the CYA is about 50-60. We have the 2000 gph pump/filter/SWG combo and salt level is already at 3100 ppm.

We've been using it without running the SWG, just the pump to filter the water and circulate it through a solar panel. Water temp is about 75F now with outside temps in the high 70's to low 80's, but that is due to drop some next week. That initial shock level of chlorine from adding the dichlor to get the stabilizer level where I need it seems to be lasting a LONG time. Is this normal at these temps?

My question is whether I should start the SWG on a timer at a short cycle (1 or 2 hours per day) now or wait until the FC drops to under 6.

Any thoughts?
 
Is it covered?

I just do not think that it is possible for the FC to only drop from 25ppm to 20ppm in 2 weeks with no addition of chlorine ... I would have expected that drop in 1 day or less.

Are you sure the SWG is not on with the pump? No pucks anywhere? Kind of silly questions I know, but something does not add up.
 
Yes, it has had a solar bubble cover on it the whole time except when in use.

The SWG is running in "FP" mode which means filter pump only (or that's what they say).
I could try programming it for just 1 or 2 hours a day which should equate to maintaining a FC level of 3-5 and see if it drops faster. I had never programmed the SWG for any hours, but who knows what if might be defaulting to.

My FC numbers same from the TF100 drop test plus the daily test shows a color well above the 5 level shown on the color bars, so I believe them.
 
I am not familiar with the intex SWG, but I am wondering if FP means that is is running whenever the filter pump is ON ... thus the high FC levels.

I think you only control is how much it is on, so actually setting a short time, might let the FC come down.
 
jblizzle said:
I am not familiar with the intex SWG, but I am wondering if FP means that is is running whenever the filter pump is ON ... thus the high FC levels.

I think you only control is how much it is on, so actually setting a short time, might let the FC come down.
Click to expand...

ManualForKrystalClearSaltwaterSystemFilterPumpModelCS8111 said:
Running the pump alone without the Saltwater System:
To run the pump alone without the Saltwater System function,
press and hold both and buttons until you hear a
“beep”, the LED display will show “FP”. The pump is now
operating alone. NOTE: The pump cannot be operated alone
under an automatic timer mode. To stop the pump, manually
turn the switch OFF.
Click to expand...

FP appears to be the "off" setting that allows the unit to still pump but not make chlorine. Isn't the Solar Cover sufficient reason for the Chlorine to stick around?
 
FP means "filter pump" which should not run the SWG, but maybe the fact that I never programmed a duration for the SWG means it is coming on all the time. I'll try programming just 1 or 2 hours a day and see if the FC drops.

Maybe the solar cover is keeping the chlorine level up, but I don't have experience on how fast it should drop if water temps are 75 during the day and 70 at night.
 
From my experience the solar cover will prevent some chlorine loss. All summer running the SWG 3 hours a day I stay at about 6.5FC each evening but if I keep the solar cover on for a couple days the chlorine will go up to 10-12 in the evenings. I have continued to run the swg at 3 hours while it was covered though.
 

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The solar covers still allow some of the UV light to pass through I think, so there will still be some loss to the sun and there is always some organics being consumed.

I do not have first-hand experience either ... just seems odd to me. Makes it seem like going away for a week vacation is no big deal ... or at this rate of loss going away for a month you would still have plenty of FC in the pool. If the water were much colder, this might be more likely, but in the 70s ......
 
I have a mostly opaque cover and if the pool is not used so kept covered the entire time then my ppm Free Chlorine loss rate is as follows (with the FC level maintained at a fairly constant level of roughly an FC that is 10% of the CYA level):

Temp . Day . Week
88ºF ... 0.7 ... 4.9
80ºF ... 0.45 . 3.2
75ºF ... 0.35 . 2.4
70ºF ... 0.27 . 1.9
65ºF ... 0.20 . 1.4
60ºF ... 0.15 . 1.1
55ºF ... 0.12 . 0.8
50ºF ... 0.09 . 0.6

Roughly speaking, the loss rate doubles every 13ºF. So losing 5 ppm FC in 2 weeks (2.5 ppm per week) at 70ºF or 75ºF is possible if the cover were rather opaque to UV or there is little sun hitting the pool. However, when at shock level, the loss rate should be higher since it's proportional to the active chlorine level where 25 ppm with 60 ppm CYA is 7.8 times higher than the numbers I show above which would be more like 6 ppm FC with 60 ppm CYA. So this does seem strange unless the baseline loss rate from oxidation of the cover, of CYA, and of any organics in the pool is a whole lot lower than in my pool.
 
Update: after letting the kids swim both Sat and Sun which I'm sure put lots of organics in the water, the FC is now down to 12 with a water temp in the low 70's. Looks like it's beginning to act much more normal now that we've actually used the pool.

I'm going to let it drop further, then start the SWG this weekend.

Thanks to everyone for your helpful information.
 
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