Very high CYA levels, HELP!

[Mindiv]

Thank you Big Dave! Repeated with the K-2006 and got 140-150 (70-75 diluted) for CYA.

[Mindiv]

Trying to explain to an old friend why high FC levels with high CYA isn't as irritating as the same FC level with lower CYA. Just trying to convince them that my pool is indeed safe! It is amazing to me how many people don't know that high CYA levels require higher FC levels.... Any references? I tried a search with no luck.

[PoolDoc]

It is amazing to me how many people don't know that high CYA levels require higher FC levels.... Any references? I tried a search with no luck.

Not that amazing to us.

I published the first material to that effect, based on my experiences and John Wojotowicz's articles in the JSPSI. Richard "ChemGeek" dug into the chemistry of it, and provided the rigorous analytical foundation for understanding the issue, based on his analysis and the O'brien article (on which Wojotowicz had depended).

About a decade after I first published the first version of the "Best Guess" chart, 10,000's of users here and at TFP have established repeated field validation of that analysis.

But, even now, only my sites (PoolForum and PoolSolutions) and TFP consistently acknowledge these facts. To my knowledge no one 'officially' in the pool industry has done so.

The same is true of the 'step-by-step' approach to alkalinity control that I originated -- even though that approach is well-established in both the potable and waste water treatment industries (though I only discovered that after the fact), only PF/PS and TFP teach this approach.

Truth, when it steps on established practices and profits, is never popular. This is just as true among evangelicals as it is among atheists; among Democrats as it is among Republicans; among industrialists as it is among environmentalists. A friend of mine once observed that trying to serve the truth is like trying to wield a sword equally sharp at the handle, as the end: no one is safe around it.

[chem geek]

If you need technical references, there is the original O'Brien paper from 1974:

Equilibria in Aqueous Solutions of Chlorinated Isocyanurate

and there is my analysis of the equilibrium constants from that paper to derive why the FC/CYA ratio is a decent proportional proxy for the active chlorine (hypochlorous acid) level:

http://www.troublefreepool.com/pool-...28.html#p50548

The bottom line is basic equilibrium chemistry where the primary chemical components at typical pool pH are the following (the ppm assume the following is the only reaction, but there are actually others that are less dominant):

HClCY- + H2O <<<---> H2CY- + HOCl
"Chlorine Bound to CYA (Inactive)" + Water <<<---> CYA + "Unbound Chlorine (Active)"
........ abt. 9 ppm Cl2 .................................... 150 ppm CYA .... abt. 0.024 ppm Cl2

Most of the chlorine is bound to CYA and the total CYA level is typically much higher than that so if the CYA level rises then you need to proportionately raise the Free Chlorine (FC) level to maintain the same amount of active chlorine. The FC measured in tests measures both the unbound and bound chlorine since the reaction above moves to the right quickly as active chlorine gets used up in the test (technically, half gets released every 0.25 seconds -- see tihs paper and this paper). Equilibrium chemistry says that the following is a constant (at a given temperature):

[CYA]*[Unbound Chlorine (Active)]/[Chlorine Bound to CYA (Inactive)]

So as CYA rises, you need to increase "Chlorine Bound to CYA (Inactive)" by the same proportionate amount to keep the active chlorine level the same. Since most of the chlorine is bound to CYA and is measured as FC, it's easiest to just say to raise the FC proportionately when the CYA rises -- which is the same thing as saying to keep the FC/CYA ratio constant.

I know, I know, TMI.

[Mindiv]

Ben and Chem Geek you both rock!! Actually makes complete sense but that would be because I was a marine bio major with serious chem background and now I'm a physician assistant and live in the scientific world. That is exactly what I thought and explained to my pool guy. He didn't understand prior to our conversation that the tests measured bound and unbound (I made a darned good guess, but based on the reality of binding to stabilize I figured that had to be the case). He had always just done the usual "Chlorine lock" crap. Referenced this forum so maybe I have created another convert or maybe he was just thinking I'm a lunatic! ;-)

Either way...pleasantly happy with my first swim in a FC of 9 and found it much more comfortable than lower levels at other pools. THANK YOU POOLFORUM!!!!!!!! Now off to read all the referenced materials. I would like to speak with authority when people question my way of dealing with my pool this season until my CYA levels are lower and frankly from here on out.

[chem geek]

In my post above, I added a couple of links to papers talking about how the bound chlorine is measured in FC tests and the reaction rates for release of chlorine from bound CYA.

I also want to note that there are two effects from the higher FC at higher CYA even when keeping the FC/CYA ratio constant. The first is that the chlorine bound to CYA is not completely "inactive" as I had indicated. As noted in the following paper:

Effects of isocyanuric acid on the monochlorodimedone chlorinating rates with free chlorine and ammonia chloramine in water

The reaction rate of chlorine bound to CYA could be as much as 1/150th that of hypochlorous acid. So an FC of 9 ppm with 150 ppm CYA would have 0.024 ppm hypochlorous acid (in ppm Cl2 units) at pH 7.5 and 77ºF temperature, but could have up to 9*(1/150) = 0.06 ppm additional equivalent oxidizing power from the chlorine bound to CYA. Since we normally aren't dealing with such high FC and CYA levels, we normally ignore this effect though it may at least partly explain Ben's experience with seeing more effects from such high levels.

The other effect is due to the higher FC being a higher capacity or reserve that will continue to oxidize when one gets out of the pool and the water starts to evaporate. This is tricky to figure out because while there is more capacity to keep on reacting for longer, it's unclear what the increase in concentration from water evaporation will do. All the chemical components increase in concentration equally and ultimately one would end up with precipitate of CYA and possibly Trichlor, but as the active chlorine level goes up it will react as well as outgas so maybe that occurs fast enough to result in only CYA precipitate and no Trichlor. So maybe there is more risk towards oxidizing skin and swimsuits after getting out of the water with high FC, but it's not at all clear if this effect is large enough to be noticeable (i.e. I'm just speculating here). A decent experiment for this would be to notice any difference in chloramine smell on your skin in the high FC and CYA vs. lower FC and CYA (but both with the same FC/CYA ratio), but of course you'd have to have the same sweat conditions for a decent comparison.

Compare this with what is typically the case in many indoor commercial/public pools that use no CYA. Even with 1-2 ppm FC, they have at least 10-20 times the active chlorine level of the outdoor residential pools following Ben's chart. That's a HUGE difference in oxidation rates of swimsuits, skin and hair as well as in the rate of creation of disinfection by-products including smelly and irritating nitrogen trichloride. My wife experienced this difference every year when she swam for 5 months over the winter in an indoor community center pool. She had to buy new swimsuits every season as their elasticity would get shot and her skin would be flaky and hair frizzy. In our own pool used 7 months over the summer season, her swimsuits would last for 7 years and the effects on her skin and hair were noticeably better.