- Aug 28, 2019
- 215
- Pool Size
- 12000
- Surface
- Fiberglass
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Turbo Cell (T-CELL-5)
First of all, let me begin by saying this isn't an indictment or skepticism of this community or the TFP methodology. This is a genuine open-ended request for more detailed info mostly out of curiosity, and also due to the fact that a lot of the concepts and principles on this site challenge what I learned as a pool pro once upon a time. When rules/concepts/etc get engrained in you, it's hard to accept anything that challenges them without pause. One thing I have never come across on this forum is a post declaring that any method or process developed by TFP has put swimmers or property at risk, so it's clear to me that everything here has essentially been vetted through the experience of hundreds of thousands of people. The intent of this post is not to cast doubt.
I've read the Pool Water Chemistry thread initially posted by @chem geek, and the chemistry behind the Chlorine/CYA relationship made sense to me, even with my 10th grade-level understanding of chemistry. It even got a nod of approval from my usually skeptical father-in-law (also a pool owner), who has a PhD in chemistry and was a chemist for Dow and 3M over his 40 year career.
There's one thing that wasn't clear to him, isn't clear to me, got an alarmed eyebrow-raise from my wife, and got a full on "stop what you're doing right now" response from my own father, a man with a doctorate degree in public health who did research for the NIH and CDC for many years. That thing is the assertion that it is safe to swim in water chlorinated at concentrations below SLAM level. To get into my mindset, let's break down what I learned about chlorine 15 years ago when I was getting my certificate to manage and operate a public pool:
I've read the Pool Water Chemistry thread initially posted by @chem geek, and the chemistry behind the Chlorine/CYA relationship made sense to me, even with my 10th grade-level understanding of chemistry. It even got a nod of approval from my usually skeptical father-in-law (also a pool owner), who has a PhD in chemistry and was a chemist for Dow and 3M over his 40 year career.
There's one thing that wasn't clear to him, isn't clear to me, got an alarmed eyebrow-raise from my wife, and got a full on "stop what you're doing right now" response from my own father, a man with a doctorate degree in public health who did research for the NIH and CDC for many years. That thing is the assertion that it is safe to swim in water chlorinated at concentrations below SLAM level. To get into my mindset, let's break down what I learned about chlorine 15 years ago when I was getting my certificate to manage and operate a public pool:
The health department required a minimum of 1 ppm free chlorine (2 ppm when using dichlor or trichlor) with an ideal target of 3 ppm free chlorine. The maximum allowed by the health department for a sustained period while bathers were in the water was 5 ppm. If FC levels above 7 ppm were detected, the pool had to be closed to swimmers immediately. Any FC levels 10 ppm and above constituted an "immediate hazard" to the health of swimmers; if such levels were detected while swimmers were in the water, the health department had to be notified immediately (as with readings under 1 ppm). The 10 ppm upper hard limit was partially due to the fact that ph is no longer accurately measurable above 10 ppm FC, and some health departments almost treat ph with greater reverence than FC. But, it was also clearly explained that allowing bathers in water with a FC concentration above the 10 ppm mark could cause significant dermal distress or respiratory distress.
Now of course, we're talking about a public facility with a wide range of swimmers, some of whom could have respiratory illnesses, etc. There's also the concern of lawsuits and the like. But still, when it gets beat into your head that anything above 10 ppm is an immediate hazard to health, and then you're introduced to a concept that says swimming in water with concentrations below SLAM level - even if that level may be 20+ ppm - is safe, it's a hard idea to grasp. I've looked all over this forum and haven't found anything that scientifically and concretely explains why it's safe to swim in water as long as it's below the SLAM level, and I'm hoping someone can either explain it to me or point me to a thread that does. I get that it has to do with the relationship of chlorine to CYA, but I'm interested in knowing what specifically makes (for example) an FC of 18 unsafe at CYA levels of 40, but safe at CYA levels of 50. 
