What's the association between chlorine and CYA?

[gonefishin]

Hi all,

I do have a question regarding chlorine and how it interacts with CYA.

What is it with "unprotected" chlorine that allows it to be used up by a warm sunny day?

Also...

What is the interaction between CYA and chlorine that seems to protect and stabilize the chlorine in water?


When CYA levels raise, why is it that additional amounts of chlorine are needed to reach a disinfecting levels.

Does the CYA "lock up" partial amounts of chlorine...so that they aren't available for either disinfecting...or even some of the ill effects of higher chlorine levels. As if all the chlorine is not available for use at higher CYA levels?

thanks,
dan

[aylad]

The way it was explained to me is that the CYA acts like an umbrella for the chlorine in your pool. The chlorine that's under the umbrella isn't sanitizing your water, rather, it's more like sitting there waiting to be "called up". The chlorine that can't fit under the umbrella and is loose in the pool is what is sanitizing your water. As it gets used up by goo in the water, or consumed by the sunlight from which it is unprotected, a little more of the chlorine moves out from under the umbrella and goes to work. This is why it stays in the pool for longer periods with higher CYA levels--there is less of the chlorine working at any one time, but a much larger reserve for when the working chlorine is used up.

Don't know if that helps or not, but that's how it works in my mind.......

Janet

[gonefishin]

Thanks Janet

I've found a good number of websites that also explained the role that chlorine, CYA and other chemicals play in pool water. It's really quite interesting...and really gives me an idea why it's so advantageous to treat your water as described at this forum. Treat and correct the water from the beginning...then maintain correct levels with chemicals that cause minimal changes to other areas in your pool water.

I've still much to learn...but I am learning

thanks,
dan

[mwsmith2]

What is it with "unprotected" chlorine that allows it to be used up by a warm sunny day?

Also...

What is the interaction between CYA and chlorine that seems to protect and stabilize the chlorine in water?

WARNING: CHEMISTRY GEEK STUFF AHEAD!


Well, Cl is an unstable compound, and it happens to be very unstable in sunlight because its absorption maxima is around 290 nm. That's the UVB range that gives you sunburn. So, if you could erect a huge UV shield over your pool, you wouldn't need stabilizer. That's neither practical nor cost-effective though!

However, when you mix Cl with cyanuric acid you end up with chloroisocyanurates, a compound that the absorption maxima is well below 290 nm. This is great for us because wavelengths below 290 nm are absorbed by the atmosphere. This also happens to be why the sky is blue.

So that's the slightly techical short answer of why cya works.

Michael

[MaryLee]

Well, Cl is an unstable compound, and it happens to be very unstable in sunlight because its absorption maxima is around 290 nm. That's the UVB range that gives you sunburn. So, if you could erect a huge UV shield over your pool, you wouldn't need stabilizer.

That's why indoor pools don't need CYA.......right?

[gonefishin]

That's why indoor pools don't need CYA.......right?

Right. The indoor pools aren't exposed to direct sunlight...so they don't benifit from the CYA.

'least that's the way I read it

Michael...

thanks for the comments. While doin' some reading I found it just as fascinating that chlorine is effected by high/low PH readings as well as CYA and sunlight.

It's actually a good feeling to know why my water is clear and clean. I just hope it provides me a slight leg up should a problem come up


thanks,
dan




dan

[mwsmith2]

That's why indoor pools don't need CYA.......right?

Absolutely correct.

Michael

[waterbear]

WARNING: CHEMISTRY GEEK STUFF AHEAD!


Well, Cl is an unstable compound, and it happens to be very unstable in sunlight because its absorption maxima is around 290 nm. That's the UVB range that gives you sunburn. So, if you could erect a huge UV shield over your pool, you wouldn't need stabilizer. That's neither practical nor cost-effective though!

However, when you mix Cl with cyanuric acid you end up with chloroisocyanurates, a compound that the absorption maxima is well below 290 nm. This is great for us because wavelengths below 290 nm are absorbed by the atmosphere. This also happens to be why the sky is blue.

So that's the slightly techical short answer of why cya works.

Michael

More chemistry geek stuff!
Chloroisocyanurates are a form of 'combined chlorine' that fall in a group known as chloramides. They will test as FC but do not have as high an "oxidantion potential" as FC. This means that they are not quite as good an oxidizer and sanitizer. Also , as more cyanuric acid is added to the water it shifts the equalibrium of the reaction to less FC and more chloroisocuanurates which is why you need to put more unstablized chlorine in when the stabilizer is higher...to shift the equilibrium point back and balance out the amount of FC and cloroisocyanurates in the water once again. This is why Ben's 'best guess' chart works. Once again, slightly short of a technical answer.