WARNING: This post is rated "CN", and is for Chemistry Nerds only!

Quote Originally Posted by waterbear
Low temerpature can slow or inhibit the precipitation of the melamine in the CYA test. It would be best to allow the sample of water to come to normal room temperature indoors before doing it if the outside temp is cold. It would also be a good idea to let the test bottle sit for a few mintues and then shaking again before transfering to the measurment tube (with the black dot on the bottom) to insure a more accurate reading.
Evan, while that may be true, it's very, very common for pools to be opened to ZERO CYA, even when they were closed to high levels. I'd noticed this for years, before I understood the cause, which is biodegradation of CYA. I stumbled across the cause while investigating simazine, which used to be used as an algecide. It turns out that the biodegradation of simazine involves common soil bacteria. As it happens, these bacteria usually happen to be present in pool biofilms. And, it further turned out that CYA is an intermediate of this process.

So while no one started out to study the biodegradation of CYA, it happened that they did so, along the way of numerous University and EPA funded studies of pesticide breakdown. I usually try to avoid going too far in explaining this stuff, but with your college chemistry background it should be a breeze.

Information about this is much more common now, than it was when I stumbled across it. But, it still hasn't penetrated into the pool industry.

Here are some links:

http://www.pubmedcentral.gov/article...i?artid=106326
http://en.wikipedia.org/wiki/Atrazine
http://umbbd.ahc.umn.edu/cya/cya_map.html

To quote from the last link,
"Cyanuric acid is widely used in swimming pools and is generated as a metabolic intermediate during the bacterial metabolism of s-triazine pesticides. (Karnes, 1999). It is further metabolized by bacteria and fungi via hydrolytic enzymes that ultimately release the nitrogen as ammonia. For twenty five years, it was thought that cyanuric acid metabolism proceeded through urea as an intermediate. More recent studies (Cheng et al., 2005) have shown that urea is derived from spontaneous decarboxylation of allophanate during purification of metabolites. Thus, cyanuric acid metabolism to 3 mol of ammonia is now shown to proceed exclusively via biuret and allophanate."

Please note the bit about urea and ammonia -- it's this part that's so very relevant to the spring time problem some have of adding chlorine in huge quantities, but never getting a residual: they are trying to oxidize all that ammonia!

As a concomitant, they will often note that all the algae is dead, and the pool is very clear. This happens if the pool pH happens to remain at a high (7.8+) pH level. In that case, much of the ammonia is oxidized to monochloramine, which is more effective against many forms of algae and especially, biofilms, than free chlorine. (The whole Yellow OUT process is based on monochloramine creation.)

On the other hand, if their pH is low (7.2 or less) they'll tend to form dichloramine and nitrogen trichloride, neither of which are good for much anything, but are both very 'stinky' with what most people think of as a chlorine odor.

You can investigate this further by using the following term groups:

"cyanuric acid atrazine pathway" or
"cyanuric acid atrazine biodegradation"

Ben