Pool Math: "Your target is outside the suggested range"

LGLDSR73

Active member
Jun 26, 2019
28
Boston
I am having an issue with Pool Math per the two attachments (could not fit entire screen in one capture). It is telling me that "Your target is outside the suggested range". I believe I need to SLAM the pool in the the CYA has been creeping up and is now at .4. This pool is in the direct sun from sunup through sundown so it takes quite the beating from the UV. This morning the FC was at 6.0, CC at .2. With respect to the latter I've read that if the CC is above .2, no swimming. In any event no one was home today although the pump was run for approximately four hours. Information on the pool, pump, below my signature.

At 1800 the following readings were taken:

FC: 3.8
CC: .4
pH: 7.5
T/A: 80
CYA: 35

I am unsure why Pool Math, which is automatically populating the SLAM Target FC field, is stating that it is out of range. I will get the same message if I put a different figure in such as 10, 12, 9, etc., in that same field.

Thank you!

Skip

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Intex 18' x 9' x 52" UltraFrame Retangular
4,545 gal
Hayward T166 Sand Filter w/1HP Motor

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frogabog

Gold Supporter
LifeTime Supporter
Jul 16, 2010
2,833
Portland, Oregon
That message is linked to the "suggested range" part of Pool Math which is for maintenance mode. You can ignore it.

It is safe to swim if your FC is at SLAM level or below for your CYA level.

How are you doing your testing?
 

LGLDSR73

Active member
Jun 26, 2019
28
Boston
Hi,

Thanks for the really quick reply. Taylor K2006 test kit...should have bought the K2006C. What are your thoughts on the high CC of .4? Safe to swim with the CC at that level?

Skip
 

frogabog

Gold Supporter
LifeTime Supporter
Jul 16, 2010
2,833
Portland, Oregon
.4 is not high. It's very very low.

We're going to call your CYA 40 instead of 35. Since you can't measure between the lines on the CYA test, we round up.

For 40ppm CYA your minimum is 3ppm and your target is 7ppm. That means that you will want to target high at 7ppm usually at night, and expect to lose ~50% of that by the next evening without swimmers when you re-dose back to target with chlorine. Sun degrades around half the chlorine all on it's own, but if you've got swimmers you probably will need a little more on those days.

I do 1ppm over target each night so I can be sure to keep ahead of unexpected swimmers or other biological agents, so pool math always tells me I'm out of the suggested range.

Go put chlorine in!
 

frogabog

Gold Supporter
LifeTime Supporter
Jul 16, 2010
2,833
Portland, Oregon
You never want to fall below your minimum, that's when algae grows. If, as you suspect that you need to SLAM chances are you won't be able to hold your target and minimum.

If you bring your FC up to 10ppm tonight you can do an OCLT to see if you need to SLAM.

I suggest brushing up on these links, and check out some helpful TFP videos:
ABCs of Pool Water Chemistry
Overnight Chlorine Loss Test
SLAM Process





 

LGLDSR73

Active member
Jun 26, 2019
28
Boston
Thank you very much for your time and wisdom, really appreciate it. I put in enough Chlorine about an hour ago to reach 6.0, should have rounded up on the CYA. Will use Pool Math and add enough Chlorine to get the FC to 10ppm for an OCLT. Thanks also for the video links!

Best,

Skip
 
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5odaw1s

Active member
May 6, 2019
31
Gainesville Georgia
Hi Skip,
I believe the FC section is telling you that your target is outside the suggested range because you have activated the SLAM chlorine level. That is, the button to the right of SLAM has been pushed to the right and the button is blue.
Since the Recommended Free Chlorine range is 3.0 - 7.0 and the SLAM target FC shows 14, you are out of the suggested Free Chlorine range.
If you slide that button to the left it should turn the button white and the Slam Target FC will change to FC Target Range and the number will change from 14 to 5, which is the FC Target for 35 or 40 ppm CYA.