What level do you keep your CYA, and why?

[TomAtlanta]

Pool school recommends 30-80. That is a wide range. I'm curious what members here do, and why.

I'll answer my own question: I set CYA to 50 because it is in the middle of the recommended range here.

 

[msgtdan]

Right now I'm 35-40 because I plan to use pucks while on vacation this summer and I normally use liquid chlorine. I plan to end the summer around 50 because I get full sun from mid morning to sunset.

 

[jblizzle]

Keep reading Pool School.
30-50 for bleach pools
70-80 for SWG pools

On the higher end if you have a lot of sun.

 

[chem geek]

Mine's at 40 ppm and I've had it at 30 ppm in the past. I have a mostly opaque safety cover so do not need the CYA to be high because the pool is only open for an hour or two every day though longer (3-4 hours each day) on weekends. I decide to raise it a little to 40 ppm since I only have to add chlorine to the pool twice a week and a higher CYA works a bit better with the chlorine swing from 6 to 3 and back again.

 

[UnderWaterVanya]

55 last year... Fell slowly to 45. This year it was less than I could measure when I opened, then I brought it to 40.

Due to massive rain this year cousin me to drain off several inches more than 5 times the cya is back to just over 30 again.

Sent via Tapatalk...

 

[cody21]

Mine is somewhere between 40 & 55 ... The CYA test is soooo subjective to my eye. But that level seems to facilitate my swings between CL low levels of 3 vs target 6 when I catch it on the low side. I pretty much try to just blindly (w/o testing) add 1/2 bottle of bleach every afternoon during the hotter days of summer & my pool temp gets to 88-90. Then once per week do the FULL test to get an accurate read on my FC & CC et al and adjust as necessary.

 

[UnderWaterVanya]

Mine is somewhere between 40 & 55 ... The CYA test is soooo subjective to my eye. But that level seems to facilitate my swings between CL low levels of 3 vs target 6 when I catch it on the low side. I pretty much try to just blindly (w/o testing) add 1/2 bottle of bleach every afternoon during the hotter days of summer & my pool temp gets to 88-90. Then once per week do the FULL test to get an accurate read on my FC & CC et al and adjust as necessary.

Honestly if it looks good and that works for you I'm sure that's acceptable. My own routine is similar with a lower cya.

Sent via Tapatalk...

 

[Richard320]

I keep mine around 50. My pool gets a lot of sun and so minimum FC is 4. Which looks just like 5 on the OTO test to me. All I really need to know is if my FC is as dark or darker than the highest color on the quick tester and I'm good, since I test just before dinner when the sun is pretty much done attacking my pool.

 

[mickey4paws]

Ours is about 40 right now, and we have a SWG so I know it's too low. I've always used the liquid stabilizer but just bought a tub of the granular kind.

Can anyone tell me what kind of sock to use? A men's sport sock or should I use a ladies nylon knee high?

Also, why is CYA for SWG supposed to be so high compared to a regularly chlorinated pool?

 

[UnderWaterVanya]

Also, why is CYA for SWG supposed to be so high compared to a regularly chlorinated pool?

It's a trade off. Higher CYA lowers FC losses allowing the SWG to work less to keep up. The consistent chlorination of the SWG reduces the risk of allowing algae to get a foothold, so the higher CYA is not as risky.

Sent via Tapatalk...

 

[mickey4paws]

It's a trade off. Higher CYA lowers FC losses allowing the SWG to work less to keep up. The consistent chlorination of the SWG reduces the risk of allowing algae to get a foothold, so the higher CYA is not as risky.

Thanks, that makes sense. On the other hand, with CYA at a higher level, the corresponding FC level has to be higher, and wouldn't that make the cell work harder too? or not?

Nevermind....I was thinking of shock level you need to be at with the higher CYA, not FC.

 

[chem geek]

Thanks, that makes sense. On the other hand, with CYA at a higher level, the corresponding FC level has to be higher, and wouldn't that make the cell work harder too? or not?

You might think so but it doesn't work out that way for reasons we don't fully understand. CYA seems to shield chlorine from breakdown from sunlight with a mechanism beyond just being bound to it, perhaps shielding lower depths from UV (though some sources say that shouldn't be the case). So even though the FC is proportionately higher so you've got the same active chlorine level while having more chlorine bound to CYA, the overall FC drop is less. This post shows the effect where the FC/CYA ratio is kept constant so the active chlorine level is the same, but the % Loss is lower at higher CYA and enough to make even the absolute FC loss lower.

 

[mfwade]

I keep ours at 50 as we get a lot of sun and minimum FC 4.

 

[agogley]

Interestingly, there has been some new studies that CYA is best at no higher than 50. In public pools, especially indoor pools, new recommendations are as low as 20!
I'm actually coming around to the idea of keeping my CYA level at about 50-60 this summer instead of the usual 75-85.

http://www.ppg.com/chemicals/accutab/Si ... visory.pdf

http://standards.nsf.org/apps/group_pub ... -store.pdf

http://www.poolspanews.com/chemicals/is ... side-.aspx

 

[jblizzle]

We too recommend 20-30ppm for indoor pools, only reason it is that high is because the tests do not go lower.

If you have little sun, you may get by with lower CYA with the SWG. Otherwise the cell is just going to have to work harder by running more and shortening its life expectancy.

 

[chem geek]

Interestingly, there has been some new studies that CYA is best at no higher than 50. In public pools, especially indoor pools, new recommendations are as low as 20!
I'm actually coming around to the idea of keeping my CYA level at about 50-60 this summer instead of the usual 75-85.

http://www.ppg.com/chemicals/accutab/Si ... visory.pdf

http://standards.nsf.org/apps/group_pub ... -store.pdf

http://www.poolspanews.com/chemicals/is ... side-.aspx

Actually, the proposed Model Aquatic Health Code (MAHC) Disinfection and Water Quality Module prohibits CYA from indoor pools and high risk venues, but they may change that to just limit to a low CYA level. The first source limits CYA because it would be too hard to shock (raise the FC) if Cryptosporidium is suspected, though if one used just 1-2 ppm chlorine dioxide overnight then that would be sufficient.

As for the sources that say CYA doesn't do anything above 50 ppm in terms of protection of chlorine, that is baloney. It's just that in high bather load pools there isn't much benefit seen above around 30 ppm because the chlorine loss from bather load exceeds that from sunlight. However, in residential pools that are nearly all very low bather load, nearly all the chlorine loss during the day is from sunlight and higher CYA levels most certainly do protect such losses, even if one raises the FC level to keep the FC/CYA ratio constant (i.e. the active chlorine level constant).

 

[mickey4paws]

Thanks, that makes sense. On the other hand, with CYA at a higher level, the corresponding FC level has to be higher, and wouldn't that make the cell work harder too? or not?

You might think so but it doesn't work out that way for reasons we don't fully understand. CYA seems to shield chlorine from breakdown from sunlight with a mechanism beyond just being bound to it, perhaps shielding lower depths from UV (though some sources say that shouldn't be the case). So even though the FC is proportionately higher so you've got the same active chlorine level while having more chlorine bound to CYA, the overall FC drop is less. This post shows the effect where the FC/CYA ratio is kept constant so the active chlorine level is the same, but the % Loss is lower at higher CYA and enough to make even the absolute FC loss lower.

Thanks so much for the reply, Chemgeek! I knew you'd be great at explaining it. It really does seem to make a significant difference, for example just in the numbers between 50 CYA and 80 CYA. I'm going to do another CYA test this morning. Yesterday's was only 40 CYA. I still don't feel totally confident in the results because for me, the CYA test is a hard one to read accurately.