Thanks for the input. That makes sense. I thought it sounded too good to be true.

Is your calcium hardness decreasing as well?

We hear about this more rapid loss in very sunny areas like Florida and Arizona. Not only will the water be warm, but the sun is pretty intense and on the pool for long periods of time. I wonder if sunlight can act as a catalyst for CYA breakdown. It does breakdown chlorine (hypochlorous acid and especially hypochlorite ion) so perhaps the intermediate free radicals that are formed (•OH •O^- •Cl and subsequently •OCl •OH) may oxidize the CYA a bit faster. This is pure speculation on my part, though is based on some reactions described in this PDF file.

The question about Calcium Hardness (CH) is very relevant since it could indicate whether dilution is a factor (that's why I tracked that carefully in my own pool).

I'm not sure if this also has an influence or was just a coincidence, but last year we had quite a few fires near us and the sky was filled with smoke and ash. I noticed a lot of ash in the filter and all over the yard. During this period, the CYA in the pool dropped by almost half. I didn't see the same decline this year so I can't think of anything that was different last year than this year which would have caused the disappearance of CYA.

Ash as a catalyst or causing interference in the test? Seems very strange to me. As waterbear said, we really just have to TEST the water's CYA level every now and then and adjust accordingly. It would certainly be nice to know what really is going on in these situations when it drops, but until we do then testing will at least let us maintain a Trouble Free Pool.

Richard

That's interesting. Bioguard used to sell something called Absorbing Agent" for it's biguanide line. It was just activated carbon. I don't know if there's any on shelves anymore, but I assume you could use ground up charcoal in it's place. A worthy experiment.

Over the month's period no noticeable change in CH. In any case my CH has a tendency to increase slightly over time.

Just found this note on the LaMotte site:



link: http://www.lamotte.com/testingtips/Colo ... 20Tips.pdf

This runs contrary tot he idea that in colder water precipitation rate would be lower.
Any ideas?

Precipitation rate is slower but solubility decreases in cold water so if you let it develp to completion it will read high since more will precipitate out. Likewise, in warm water less will precipitate since solubility increases. The speed of the precipitation has nothing to do with the solubility of the precipitate. The reaction will procede faster in warm water than cold water. LaMotte specifies a temerpature range and time range for the test because that is how their meter is calibrated. This time and temp range does vary smewhat with the different meters they offer.
There is no discrepancy.

I just updated the first post in this thread to show bacterial chemical pathways that allow further oxidation of ammonia to nitrate and nitrogen gas. This should resolve the mystery of disappearing CYA that does not result in high chlorine demand. Unfortunately, it is not easy to control which pathways are used since some are aerobic (require oxygen), some are anaerobic (are without oxygen), some require organic carbon and most are accomplished by different bacteria. At a minimum, nitrifying bacteria (such as Nitrosomonas) are required to convert ammonia to nitrite followed either by nitrifying bacteria (such as Nitrobacter) to convert nitrite to nitrate or denitrifying bacteria to convert nitrite to nitrogen gas or Annamox bacteria to convert nitrite and ammonium ion to nitrogen gas.