Degradation of Cyanuric Acid (CYA)

[toofast]

I'm not sure if this is the correct thread but the title sure hits it...

for the past 3 years I end the winter with 60 parts per million to cya

I use the trouble-free pool method for opening and closing and everything else straight bleach. nothing else.

yet every spring my cya is back to nearly zero....

I've tried reviewing all the threads but has there been any update on this phenomena over the years?

 

[Newdude]

yet every spring my cya is back to nearly zero

You lose a few ppm per month to degradation. It's not noticeable during the season but adds up when you walk away from the pool for 6 to 8 months.

Then your mesh cover lets rain dilute it further. You get about 3 ft a year in northern Ohio, plus any melted snow.

 

[HermanTX]

Do you mix the water before taking a sample? Rain water on top can be zero CYA while the pool water you started with may have some CYA.
CYA can degrade over time - it is a slow process.
maybe @Newdude has some thoughts.

 

[Newdude]

maybe @Newdude has some thoughts.

Already Marty'd ya.

 

[toofast]

All righty thank you and yes I mix up the water. the pool's been running for a few weeks but it makes sense with the degradation and the rain blah blah blah

thanks,

 

[JoyfulNoise]

There’s bacteria that will convert CYA to other compounds for energy and not always convert it to ammonia. But it’s more than likely that dilution from winter precipitation lowers it the most dramatically.

 

[sduda210]

I test the water in October before I close. I usually have 50 ppm CYA at the end of the season. I lower the water to below the returns and allow it to fill with rain over the winter. With the combination of dilution and degradation I open the pool in late April with less than 20 ppm. I see it as a benefit since I always open with bringing the water up to SLAM level. The lower the CYA, the lower the CYA level.

 

[Chasarms]

I don't know why, but I lose CYA all year around. I know that there is evaporation, splash out, rain, backwashes, etc. In any case, I lose about 10 ppm per month. I have every year I have had the pool.

 

[CountryBoy19]

I'm going to chime in as well. I know the general consensus is that CYA doesn't significantly decrease with time but it absolutely does, and in my case I'm certain I have the setup to prove it. My pool has a Coverstar pool cover and we have kids. The ONLY time my pool isn't covered is when we are using the pool or performing some type of maintenance activity. The cover is 100% opaque (zero light passes through), prevents 99.9% of rain entry, and my CYA loss is significant and it happens both in the summer and in the winter when the pool is winterized and sealed off (that should eliminate all splash-out, dilution, evaporation, light-related, air-related, & heat-related causes of CYA loss).

This thread hypothesized that heat combined with elevated chlorine levels causes oxidation of the CYA but my wintertime loss proves that incorrect. CYA Dropped on it's own?

Immediately prior to winterizing my pool (I don't drain, I plug all returns and the skimmer, then place ETOH filled bottles in the skimmer to prevent expansion of ice) I make sure my CYA level is above 50 ppm. I usually winterize in late October. Every April when I open the pool my CYA level is 0. So in 6 months time I have lost all 50 ppm. That's not "a few ppm per month", that's almost 10 ppm per month. I hypothesize that CYA naturally decreases through internal pool chemical reactions, by approximately 10 ppm/month. I think pool school/pool math/common wisdom here should be amended to reflect this because it was the most challenging pool chemistry issue for me when I opened the pool up on year 2. I learned here that CYA doesn't disappear except by draining and replacing water. So spring of year 2 I was not prepared to add a bunch of CYA. I opened the pool and the level was 0. I didn't have enough CYA in hand and at that time Walmart didn't carry CYA so I had to drive 2 hrs round trip to the store I normally got my pool chems from.

 

[JoyfulNoise]

Most pools don’t lose CYA to any significant degree. I’m my own pool I can go all winter and lose maybe 10-20ppm over 6-7 months. I lose more CYA in the summer due to intense UV and heat causing oxidation than I do in the winter. So where my pool sees greatest CYA loss (10-15ppm per month) is over the summer.

TFP teaches to average/expected cases within the norm, not the outliers. For the vast majority of pools, CYA loss through processes other than water exchange is not a significant factor in pool water management. This is why TFP also teaches the key concept of regular water testing using one’s own test kit. Every pool is slightly different and so it’s important to learn what your pool needs and how to modify pool care so that it’s meets your pool’s needs.