Does winter (midwest) impact CYA levels?

[chem geek]

OK, I've made some progress in answering this. The PDF file accessed in this link describes how the key to degredation of CYA is an absence of dissolved oxygen. Ironically, colder water holds more dissolved oxygen than warmer water so that is counter to what happens in the winter when you close your pool. If the pool is covered, then perhaps oxygen gets used up in the pool. The article refers to chlorinated isocyanurates as sources of CYA so that would mean chlorine would be present and apparently this doesn't stop the degradation process. It seems that this process is catalyzed by biological processes (bacteria, fungi), but that just means it happens more quickly, so perhaps CYA breaks down all the time and that something about winter pools increases this rate.

So, do you both (Jean and watermom) cover your pool? Jean mentioned that the pool would get frozen; how about watermom's pool?

The reason I'd like to figure out exactly how the CYA gets broken down is that it might point a way towards reducing CYA in pools without a drain and refill (or waiting for winter).

Richard

[DerekM]

I am another one who opens with little or no CYA every year. Pool is closed in mid-October with a winter cover, is frozen several months, and, around May 1st, I always open to a clear pool, with little or no Cl and CYA. To reduce maintenance now that swimming days are scarce, I am running out the season with pucks, as I know from experience that whatever CYA I am adding will dissipate over the winter.

- Derek M
PEI Canada

[Watermom]

I usually do cover my pool, however, last fall my cover came off (with a little help from my two golden retrievers, but that is another story!) around the beginning of November. Since the bulk of the leaves had already fallen, I decided to just leave it uncovered the rest of the winter. My water remained clear and pretty clean. Here in south-central WV, my pool doesn't get much ice. Occasionally a glaze, but not a frozen pool by any means.

[chem geek]

Some more detailed technical info is at this link which specifies a specific enzyme (cyanuric acid amidohydrolase) that is key to the breakdown of CYA. This enzyme is found in some bacteria (including Pseudomonas and a strain of Escherichia coli; the former is generally hard-to-kill while the latter is easy-to-kill by chlorine). [EDIT] This link describes another bacteria (Ralstonia basilensis) found in soil that degrades CYA (there are also fungi in soil that breakdown CYA). It should be noted that the final products of the breakdown of CYA are carbon dioxide and ammonia so if chlorine is also present, then the ammmonia should breakdown to nitrogen gas. [END-EDIT]

Though degradation by bacteria is a clear pathway for reduction of CYA over time, I don't like that since such bacteria shouldn't exist in pools with sufficient chlorine levels and if hearty ones did (such as Pseudomonas), what does that say about our sanitation levels?

I'll keep researching this. As far as using an enzyme to help break down CYA, that is not practical unless one can "turn off" that enzyme by destroying or disabling it after one is through using it.

Richard

[nicole12]

I too properly close my pool and when I open in the spring, I have very little to no CYA and I run high CYA levels due to trichlor. And when I open in the spring, the water is crystal clear. I of course need to shock and get all my levels back up but the water is not green.

[chem geek]

I just received a new CYA test kit (from Taylor) that measures down to 20 ppm CYA instead of 30 ppm that I had previously. At the start of this season, I had just under 20 ppm (perhaps it was 15 ppm) of CYA, but when I measured it today it was way, way less than 20 (not quite clear, but only very slight cloudiness) so it appears that I lost most of of my CYA during the summer. I have a cartridge filter so there is no backwash and we have very little splash-out so the dilution is minimal (and my CH reading didn't go down so there wasn't any sort of general dilution). This didn't seem to affect my chlorine consumption much since I keep the pool covered (electric opaque pool cover) and when it's open for swimming the pool is about 1/3rd to 1/2 covered by shade anyway.

So, I'm thinking that perhaps CYA breaks down all the time though at a very slow rate and it is either most noticeable over the winter or perhaps keeping sun away from the pool ironically makes the CYA break down faster (doesn't make sense, but who knows).

Richard

[NWMNMom]

Just a question, if you have an AG pool, don't you plan on a partial drain to below the skimmer and returns anyways to prevent skimmer/return ice expansion damage? That step right there would lower your startup CYA because you have to add water in the spring....

[chem geek]

My pool is in-ground, but it is true that I dilute it with winter rains and that lowers the CYA level, but I've accounted for that. What I don't understand are the reports of people losing virtually all of their CYA over the winter when they aren't doing a drain/refill. You are right that some people may be doing a partial drain/refill to get below the skimmer in cold climates (it doesn't snow where I live near San Francisco and only sometimes gets to freezing -- the pool water never freezes) and that would lower CYA levels, but people are reporting all of their CYA going away even when they start out with high levels.

I will keep better track of my CYA levels now through next year's summer season and perhaps there is a normal but slow degradation of CYA that occurs and that, for reasons I can't explain (yet), it's either more noticeable over the winter or occurs much more rapidly over the winter. The anaerobic bacteria explanation is real as some of them do consume CYA, but I just don't like the idea of having such bacteria survive in a chlorinated pool.

For now, I'm boosting up my CYA level (since it's nearly gone) and will see what happens over the winter and next summer.

Richard

[Watermom]

Just a question, if you have an AG pool, don't you plan on a partial drain to below the skimmer and returns anyways to prevent skimmer/return ice expansion damage? That step right there would lower your startup CYA because you have to add water in the spring....

Yes - but when you drain below the skimmer and returns, you actually don't throw out all that much water. It would lower your startup CYA level some, but not substantially.