Health department rules on FC/CYA ratios

[rock]

While researching my local health department rules on FC/CYA ratios, I happened to run into this Richard Falk (aka chem_geek) paper on the net, which I point out so that others may read it:
- The Chlorine
/
Cyanuric
 Acid 
Relationship and
 Implications
 for
 Nitrogen
 Trichloride, by, 
Richard
 A.
 Falk

Also, I noticed this paper by Robert W. Lowry which proposes a FC-to-CYA ratio of 7.5%:
- Cyanuric Acid: It Controls Your Pool

And, I found this Pool Operators of America paper on FC-to-CYA ratio chemistry:
- Cyanurics ~ Benefactor or bomb? by Kent Williams, Executive Director of the Professional Pool Operators of America

Plus, I found this repeat TFP chart on the FC/CYA ratio recommendations:

Yet, as far as I can tell from my searches today, most public heath departments, while aware of the ratio implications, still persist in prescribing static minimum FC & maximum CYA levels.

For example, this quote shows that the Oregon public health department knows the relationship:
http://public.health.oregon.gov/Hea...PoolsLodging/Documents/pooltrainingbook09.pdf

"Crypto CT inactivation values are based on killing 99.9% of Crypto. This level of Crypto inactivation *cannot be reached* in the presence of 50 ppm chlorine stabilizer, even after 24 hours at 40 ppm free chlorine, pH 6.5, and a temperature of 77°F (25°C). †† Extrapolation of these data suggest it would take approximately 30 hours to kill 99.9% of Crypto in the presence of 50 ppm or less cyanuric acid, 40 ppm free chlorine, pH 6.5, and a temperature of 77°F (25°C) or higher.

Where the †† indicates this reference source:
Shields JM, Arrowood MJ, Hill VR, Beach MJ. The effect of cyanuric acid on the chlorine inactivation of Cryptosporidium parvum. J Water Health2008; 7(1): 109–114.

I'm searching for a public health department fact sheet that understands that the FC/CYA ratio (and not static levels) is what is important, but, I can't find any yet.
For example, this Lincoln Nebraska public health department "fact sheet" on CYA still persists in listing static minimum FC and maximum CYA levels:
- Fact Sheet on Cyanuric Acid and Stabilized Chlorine Products

Same with this Oregon Public Health Division "Pool Operator Training Manual".

So, if anyone here knows of any public health department which prescribes the RATIO of FC to CYA, that would be a useful reference.

 

[chem geek]

Re:

So, if anyone here knows of any public health department which prescribes the RATIO of FC to CYA, that would be a useful reference.

There are none. No public health department in any county or state uses the FC/CYA ratio. They all use separate FC and CYA ranges. This is also true for the CDC (including the proposed Model Aquatic Health Code, MAHC) and EPA (for labeling rules).

As for Bob Lowry, he took the 7.5% from me (a good portion of his article came from posts I've written on this and other forums and I also reviewed what he wrote and gave him comments), but he did a long time ago propose a 10% ratio (as the inverse so have your CYA at 10 times your FC level and his context was the CYA level needed for protection). The true originator of the FC and CYA relationship was Ben Powell and I then determined the FC/CYA ratio rule after that. Of course, the 1974 O'Brien paper gives the detailed equilibrium constants to figure this all out, but they didn't propose standards based on the ratio -- they just cautioned on using too much CYA.

 

[rock]

Re:

No public health department in any county or state uses the FC/CYA ratio. They all use separate FC and CYA ranges. This is also true for the CDC ...and EPA

Hi Richard,
Thanks for answering. I googled for quite a while, so I'm glad you've confirmed my suspicions that the government doesn't subscribe to a FC-to-CYA ratio.

Given that clear answer, I'm confused what I'm supposed to "infer" given the fact the government simply specifies a static minimum FC value (usually >2 ppm) and a separate static maximum CYA value (usually <<100 ppm) for reasons that there isn't much added value at those higher levels:

Causing further confusion, that one CYA paper by Kent Williams also seems to infer that the FC-to-CYA ratio isn't all that important, even while clearly showing that CYA inhibits the sanitizing action of the chlorine (where the doublespeak confuses me).

For example, in his "Figure 1", he shows the more CYA you have the more the CYA reduces the sterilization effectiveness of whatever amount of chlorine you have. But it also shows that a low levels of CYA, e.g., at 20 ppm, having chlorine of 1.5 ppm is apparently still high enough for effective sanitation. At the other end of the curve, e.g., at 60 ppm CYA, while the CYA further reduces the effectiveness of the chlorine, adding even more chlorine doesn't seem to have much effect on the redox potential in that chart. We could have chlorine at 1.5 ppm or at 4 ppm, and the chart shows it at almost the same, such that, I'm confused whether this is a losing battle trying to take chlorine up to try to make it sanitize better at the higher CYA level.

At low CYA levels, is FC at 2 ppm really an adequate level?
And, at higher levels of CYA, is 2 ppm FC really still capable of sterilizing (where going to to 4 ppm or 8 ppm FC doesn't work any better?)

It's so confusing to me.

EDIT: So, I'm beginning to see that perhaps my confusion is that most of the papers on the FC:CYA ratio are discussing *sanitation* while this Kent Williams paper seems to concentrate more on *oxidation*, both of which are (differently) affected by the FC:CYA ratio.

 

[chem geek]

His chart is completely bogus and you should not take it seriously. ORP is very inconsistent from sensor to sensor across manufacturers (see this post), especially measuring lower ORP readings. It is absolutely positively not true that the ORP all magically converges at 640 mV at a CYA of 70 ppm regardless of FC level. Even measuring the same water, two different sensors differed by 100 mV or more in 23% of the pools that had the additional sensors. See below where I show a graph of FC vs. ORP and the HOCl vs. ORP (this comes from this post which describes more details):

https://www.troublefreepool.com/~richardfalk/pool/FC-ORP.gif

https://www.troublefreepool.com/~richardfalk/pool/HOCl-ORP.gif

I would say that an R² coefficient of determination of 0.736 is substantially more correlated than 0.109, wouldn't you?

A Chemtrol and an Oakton sensor would show the following ORP (on average -- lots of variability) with a CYA of 70 ppm, 80ºF, pH 7.5:

FC	Chemtrol	Oakton
1.5	636	580
2.0	645	592
3.0	659	610
4.0	669	622

You will be a lot less confused if you stop looking at sources that don't understand chemistry well enough to articulate what is going on. Stick with the peer-reviewed papers in respected scientific journals that we try and use as our primary sources as much as possible. Many of them are listed in the "Chlorine/CYA Relationship" section of the first post in the thread Certified Pool Operator training -- What is not taught. You will find that the kill times for pathogens correlate with the active chlorine (HOCl) level.

As for Kent Williams, see this post from Ben Powell whose been around long enough to remember Kent being associated with Stranco and his biases as a result. 90+% of what Kent writes for PPOA is very good, but he's a promotor of blasting with high active chlorine levels for oxidation and ignores how this creates greater quantities of disinfection by-products. We've written about Kent and his articles in posts/threads on this forum such as Interesting CYA Article, Find a way to collaborate with the PPOA?, Good article on CYA management from a pool industry source, Effect of Cyanuric Acid on ORP (with automated systems),

This post has a chart that shows the kill times for a 3-log reduction (99.9% kill) for various pathogens when the FC is roughly 10% of the CYA level. It's at least 10 times faster than fecal bacteria reproduction rates and is a reasonable trade-off/balance between disinfection and oxidation rates vs. harshness of chlorine and creation of disinfection by-products. DIN 19643 in Europe specifies 0.3 to 0.6 ppm FC with no CYA when ozone is not used in the circulation path and 0.2 to 0.5 ppm when ozone is used. As you can imagine, it is very difficult to maintain 0.2 ppm FC everywhere in the pool. CYA is an HOCl buffer where 4 ppm FC with 20 ppm CYA is equivalent in HOCl level to 0.2 ppm FC with no CYA.

 

[Ian.H]

As for Bob Lowry, he took the 7.5% from me (a good portion of his article came from posts I've written on this and other forums .

Yes , that’s quite true , I have read Lowrys book , “pool chlorination facts” , and after having a quick skim through that paper titled “Cyanuric Acid—It controls your pool“ , he seems to have done a complete U turn on some of his views regarding CYA!

Ian

 

[karmabiker]

Great commentary gents. I just learned a lot.

 

[chem geek]

Ian,

Just as I had sent NSPF a thorough commentary on their CPO® Pool & Spa Operator Handbook™ (see Certified Pool Operator (CPO) training -- What is not taught for more details), I also sent comments to Bob Lowry regarding the Pool Chlorination Facts book and I reviewed his updates to that book as well. In terms of the FC/CYA ratio and his initial statement that was the inverse recommendation, this is discussed in this post. Bob largely took my comments to heart and updated his writings while NSPF did not.

 

[Ian.H]

Thanks for that Richard , and to be fair , you do have to give Bob Lowry credit for acknowledging his previous misconceptions on this subject.

Even though , I live and work in Spain , I have attended quite a few UK training courses and just like your NSPF , UK bodies such as the ISPE or PWTAG are very reluctant to promote the importance of the FC / CYA ratio .

Ian

 

[chem geek]

Yeah, I didn't mean to imply that Bob wasn't receptive -- he was definitely wanting to know the truth of what goes on and disseminate that info in a way that was more digestible.

A little background might be helpful to you as to why the standards bodies and industry in general don't talk about the FC/CYA relationship. It's mostly driven by the chlorinated isocyanurate (Trichlor and Dichlor) manufacturers who for nearly 4 decades have touted that "CYA doesn't matter; only FC matters". They created this controversy and had some small basis in fact for some of what they said for commercial/public pools because the situation was different there, mostly because of the larger ammonia amounts that meant more monochloramine in the water to make up for the higher CYA levels. See the thread Pinellas County, FL Pool Study 1992 (1994) for one such controversial pool study and my analysis of it.

 

[rock]

ORP is very inconsistent from sensor to sensor across manufacturer.

Hi Richard,
That makes sense.

It seems that the ORP purveyors are the ones spreading the most FUD!

Kent Williams' arguments were that ORP is the best predictor of sanitization, so, if the sensors accuracy and repeatability has a wide variation, then that shoots holes in his arguments, and that of this "Chemtrol" paper "PPM or ORP: Which Should Be Used?" and of this Myron paper "FC E™:Ground-Breaking Measurement of Free Chlorine Effectivity in a Handheld Instrument". It seems these manufacturers may be biased, in favor of their redox-reaction measuring instruments over chemical ppm tests.

As for the lack of government standards bodies defining a ratio (versus static min FC and max CYA levels), I find it interesting that they 'tacitly' admit that the FC-to-CYA ratio matters, even though their standards don't take the ratio into account. For example, this article on Cyanurics titled "Factors Affecting the Cyanuric Acid Concentration in Swimming Pools" by John A. Wojtowicz says "many Health Departments limit CA in public or commercial pools to 100 ppm because they recognize that CA affects disinfection". So, the health departments tacitly understand the ratio; but they don't prescribe it.

I tell everyone I know that has a pool about the need to maintain the FC:CYA ratio; but, as you can imagine, they want proof and I just wish the government health departments would get on board.