why is free chlorine recommendation higher with TFP experts?

topherchris

Member
Jun 2, 2019
9
Cleveland, OH
I'm not trying question any of the experts on this site; I've found this site to be incredibly helpful when opening my pool this year. However, most of the guidelines I've read suggest keeping the free chlorine level at 1-3 ppm. The CYA chart on TFP has much higher FC level recommendations. For example, my CYA level is 50 and the chart shows 4-8 ppm should be the goal maintenance FC. Is there something I'm missing? Why the higher level here?
 

justinc

Gold Supporter
Apr 3, 2019
585
Texas
Because in the USA, the EPA regulates pesticides and says that you can only be exposed to 1-3ppm in drinking water. So somebody said OK that's the safe range for swimming pools. Except we added cyanuric acid to the pool that now binds up most of the chlorine and makes it harmless. So in a nutshell, if you take the chlorine that is unbound to CYA, it's actually LESS than 1 to 3ppm. So you're maintaining the right amount of chlorine instead of some minimal amount and the having to shock every week and have your pool turn green after a storm. Make sense? The 1 to 3ppm ratio assumes ZERO CYA in the water... which with zero CYA your chlorine will burn off in 30 minute or so.... so nobody runs zero CYA. It's just not practical.
 

Donldson

TFP Expert
LifeTime Supporter
In The Industry
Jun 12, 2009
3,711
NW Ohio
Notice TFP recommendations coincide with a CYA level, but none of those other ones do? Because those standard guidelines were created before the regular use of CYA and the industry as a whole is only just starting to recognize that CYA has a strong buffering effect on the effectiveness of chlorine. If a pool had zero CYA then keeping an FC level of 1-3 would be correct. However, the active chlorine level would actually be higher than following the FC/CYA Chart. That means it would be harsher, smell worse, and fade swimsuits. Despite being far lower FC than your pool.

But don't take our word for it, swim in your pool at 50 CYA and any FC level between Minimum and SLAM. Then go swim in an indoor public pool that uses chlorine. If that doesn't convince you that there's something to this whole FC/CYA thing, I don't know what will. We also have more scientific papers you can peruse if you wish, it's quite an extensive read but very good for those so minded.
 
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Divin Dave

TFP Expert
LifeTime Supporter
Oct 2, 2013
5,450
Longview, Texas
Top,
Richard, a.k.a. Chem Geek has been pursuing pool industry for a long time about the FC/CYA and he has posted all of the technical info for us to enjoy. If you want to read the technical stuff that proves the science behind the method, well here you go!