When I started using this site 4 years ago, as a complete newbie, I quickly learned that CYA will ONLY diminish by splash-out. And yet, I have noticed my CYA has fallen from +100 levels to below 30 levels - and I have virtually NO splash out. (I add chlorine with Liquidator.) By chance I have noticed recently that some special contributors, in answers to unrelated questions on this forum, have mentioned in passing CYA "disappearance" or "a rule of thumb that CYA gets used up at 5ppm/month"

Could the experts please put this matter to rest?

Does CYA get used up or disappear naturally by means other than taking water out of the pool or hot tub?

Thanks

PS: In my part of the world, I don't find the pool maintenance people that knowledgeable, but one did say that he finds CYA levels are lower after a winter's cold.

I am no expert but here is what I understand about CYA. The rule of 5 ppm loss a month is in reference to hot tubs only. Partly because of the high temperature of the water and also there is more splash out/water loss with a smaller volume of water.

If I understand your post correctly you started useing a liquidator 4 years ago with a CYA level of 100 ppm. That must have taken alot of bleach to maintain the pool.

In rare cases high levels of ammonia can build up in a pool or certain bacteria can "eat" CYA over the winter. If you have been useing only bleach for 4 years it is possible for your cya to have droped by 70 %.

This site recommends a partial drain/refill with CYA levels over 100 ppm partly due to the cost of maintaining the chlorine/cya relationship with high levels of CYA.

Tell us more about your pools history over the past 4 years. How do you test your water chemistry and what are the latest results? You should find your pool much less expensive to maintain with a CYA level of 30 ppm. Most here would recommend a CYA level of 30 to 60 ppm depending on your weather/sun exposure.

BBBeliever, thanks for your time and post

I have been using a Liquidator for the last 3 summers. Am very happy with it, and obviously, I havent needed to add CYA. Over the years, I have seen CYA drop about 20ppm/year which is why pool now tests less than 30, having started with 100+ when I bought our house. Previous owners used dichlor.

I test religiously with Taylors K-2006 kit and maintain:
pH 7,7-7.9
TA 50-70
Chlorine 2.5-4
hardness about 350
water temp 66-80F

TA, I know is a bit on low side, but I find that pH tends to stay more constant within this band than it does 80+

pool only has 2 users so there is no splashout

Interesting what you say about bacteria over winter months. that is a possible cause of diminishing CYA, perhaps. However, I can say that pool has been spotless each "opening" with chlorine level still around 4ppm. Water has been crystal clear and oderless

will look forward to more opinions, and......THANKS

CYA does break down, but the process is very very slow at normal pool temperatures. Usually it is slow enough that it can't be measured.

There is always splashout. Splashout includes things like the water still on your body when you get out of the pool. Water is also lost when cleaning out the skimmers and pump strainer basket. You also lose water when cleaning or backwashing the filter.

Finally, CYA occasionally disappears over the winter, though this is not at all consistent.

I think I'm the one who said ~5 ppm/month. This is what I've observed in my pool over the winter; the pool stays open all year but nobody uses it between november and april, so there's no splash out in that time.

My own pool has minimal splash-out and has cartridge filters cleaned once a year so no backwashing. During the summer the CYA drops around 2-3 ppm per month as best as I can tell (I measure at the start of the season before and after adding more CYA and then again at the end of the season). I'll check again this season to see if the rate is any different than in the past. There are a few reports of more rapid CYA drops during the summer, but mostly we see the larger drops reported over the winter especially when a pool is "let go". Your 20 ppm per year is over how many summer months of use? Do you maintain chlorine in the pool over the winter? What kind of filter do you have (i.e. do you backwash/clean it and if so, how often)?

Richard, I have the pool open five months June through October. I don't add chlorine during winter months when pool is covered. But water has been clean enough to enable 4ppm chlorine to be present at opening. I backwash twice a year. Water runs clean after a few minutes. For what it is worth, last year the water level dropped 4.5 inches while pool was covered during winter months but I don't think that's relevant

I've noticed the same thing, and I do recall some other posts about CYA disappearing during the summer months. This summer, I paid attention to both the Calcium and CYA levels. I saw Calcium drop from 200 to 150 over a few months, and the CYA drop from 40 to around 20 during the same time (added very little tap water since we've had plenty of rain this year, and actually added CYA during this time). I'd say I loose about 10ppm per month.

Really not a big deal, but I've learned to stay on top of it a little more. Test CYA every two weeks now, adjust FC levels accordingly, and might add a sockfull or two of CYA once a month.

jwfrank, so 20 ppm over 5 months is around 4 ppm per month. One difference between your pool and mine is that mine is covered with a mostly opaque cover most of the time except for 1-2 hours each day so loses somewhat less than 1 ppm FC per day. Is your pool uncovered and exposed to sunlight most of the day?

If it is chlorine oxidizing CYA (perhaps accelerated by chlorine breakdown from sunlight), then as noted in this thread, your 4 ppm CYA loss would use 4*2.5 = 10 ppm FC so around 0.3 ppm per day. Not enough to be distinguishable from the loss of chlorine in sunlight.

barefooting, the CH shouldn't be dropping unless the water is getting diluted. If we figure there is 25% water dilution, then the CYA would drop from 40 ppm to 30 ppm so you really had an extra 10 ppm CYA drop which over a few months is consistent with what jwfrank is seeing at 4 ppm per month.

We'd need more people carefully keeping track of both CH (for dilution rates) and CYA to determine a typical CYA loss rate during summer (chlorinated) months.

Thanks. You're correct of course. The 25% dilution is accurate. We had quite a lot of rain this year, and my kids like to bounce on big tubes, creating waves ... which do a great job watering the deck and dropping the pool level. So, taking the typical 4ppm per month loss on top of the dilution equates to roughly 10ppm loss per month total. Guess I hadn't really considered that, and got caught with a low CYA a couple times.

Anyway, lesson learned. I just test CYA more often now. I'll try to help out and monitor this better next year (Calcium and CYA), then report back with my Calcium and CYA loss.

My two cents. I am loosing CYA due to the rain we have been having. I have had to pump down at least 8 inches of water from the pool over the past two months. I think the rain causes more of a drop than splashing.

Richard, my pool is uncovered. I have a poorly designed infinity pool, so I keep the water level five inches below the pool edge. Therefore, there is no rain-caused run-off. And there are no scuppers - meaning I clean the pool surface with a net more often than others. But again, no water loss (hence CYA loss) via these channels

( on this topic of scuppers, are there any floating scuppers that work?)

From these posts, i summarize: it seems like there is CYA loss naturally in the course of a year, and one cannot assume it stays constant except for splash -out type water loss

I would say that is correct. There is a slow loss of CYA in chlorinated pools. The rate of such loss varies somewhat (it is probably temperature-dependent) but after accounting for all dilution sources, it may be in the range of 2 ppm per month for pools not exposed to sunlight to 4-5 ppm per month for those that are. We already knew that in covered hot spas the loss is around 5 ppm per month. There are much larger losses that are sometimes seen when a pool is let go over the winter (i.e. chlorine gets to zero). Unfortunately, both of these types of losses are not completely predictable so testing the CYA level occasionally is recommended, especially on spring startup and before winter closing and possibly once during mid-season.

Thanks again, Richard