Shock levels vs slightly elevated Levels

A_kraker99

Well-known member
Jul 18, 2015
103
Zeeland MI
What makes the recommended shock level so special? Is it not enough to just raise FC to levels to an elevated number not necessarily at shock level?
I ask because I have a slightly cloudy pool after letting it dip below minimum FC levels for a little while. I promptly raised FC to around 15 (shock level is 20) but it seems that 15 is not cutting it. Is that just because once algae takes hold it can grow quicker than sub-shock levels can contain it?
 

duraleigh

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Apr 1, 2007
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We all wish these chemistry issues were black and white but they are not.
Is that just because once algae takes hold it can grow quicker than sub-shock levels can contain it?
Very possibly. The whole idea in the SLAM is to really blast the organics fast an hard and decisively. Using less than the SLAM value could be construed as playing pattycake with the algae.

So, the numbers TFP has developed and published over the years is a guideline wherein we try to suggest as much chlorine into your pool as possible yet still be safe.
 
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A_kraker99

Well-known member
Jul 18, 2015
103
Zeeland MI
Great. So higher levels take care of it quicker. I like the pattycake reference. haha.

Its my understanding that the CYA chart Shock levels on this site are still actually safe levels for swimming. Correct?
 

bmoreswim

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Yes, it’s safe to swim up to SLAM levels of FC so long as the the bottom of the pool is visible, for safety reasons.
 

mgtfp

Bronze Supporter
Mar 5, 2020
301
Melbourne, Australia
I liked what another TFP member described for his safe swimming limit. To calculate target FC or SLAM level, he uses FC according to rounded up CYA test result, but as a safe swimming level he uses rounded down CYA level. I.e. if dot in the CYA test disappears between 50 and 60, he'd SLAM according to CYA 60 (FC 24), but use CYA 50 to determine FC 20 as a safe swimming limit. In the end it gets down to how much you trust your CYA test.