Question about CYA/chlorine relationship

[flyboy320]

According to the chlorine/CYA chart, if my CYA is at 40, then I need to shoot for min of 3, and a target of 5. If my CYA is 80, then I need a min of 6, and target of 9 for the chlorine. lets say pool "A" has a CYA of 40, and pool "B" has a CYA of 80, and they are both at the target levels of chlorine. If the conditions are the same for the pool usage, will the drop in chlorine be the same for each pool over say a one day period? In other words, would you have to add the same amount of chlorine to each pool every day to keep the target amount of chlorine in the pool?

 

[frustratedpoolmom]

No, probably the pool with the higher CYA will lose less FC daily.

 

[Richard320]

According to the chlorine/CYA chart, if my CYA is at 40, then I need to shoot for min of 3, and a target of 5. If my CYA is 80, then I need a min of 6, and target of 9 for the chlorine. lets say pool "A" has a CYA of 40, and pool "B" has a CYA of 80, and they are both at the target levels of chlorine. If the conditions are the same for the pool usage, will the drop in chlorine be the same for each pool over say a one day period? In other words, would you have to add the same amount of chlorine to each pool every day to keep the target amount of chlorine in the pool?

We'll have to wait for Chemgeek to get the real answer, but I say yes.

I have to keep my Chlorine up high - 11 to 17 - because I am stuck with high CYA and a drain is not feasible. Water restrictions, etc. It took a lot to get the level up, but I generally lose 1½ ppm/day. And from what I've read, that's not unreasonable for a pool that is in the sun almost all day.

 

[flyboy320]

Thanks guys.

What I'm trying to figure out, is how then do you decide what CYA level to shoot for? In my case I have CYA at 40, but I'm wondering if there is any advantage to say a level of 30, or maybe even 50?

 

[baudilus]

From my understanding of other posts on the subject, the pool with the higher CYA will lose less chlorine to sunlight on a daily basis.

Incidentally, the thread I am recalling was about why pools chlorinated by a SWG have the higher CYA recommendation. The explanation was that although the chlorine level required was higher, the amount needed to maintain the minimum level was lower due to less loss to sunlight.

Using made up numbers:

40 CYA - pool loses 2 ppm of chlorine per day to sunlight.
80 CYA - pool loses 1 ppm of chlorine per day to sunlight.

In either case a SWG would need to replace the lost chlorine, but the higher CYA means it doesn't have to work as hard.



Shocking at high CYA is a nightmare, but since a SWG generator is largely automatic, the likelyhood that shocking would be necessary is low, so you can get away with the higher CYA.

You could go with the higher CYA in a manually chlorinated pool as well; you just need to be diligent about adding chlorine and not letting it get too low.

Sorry for all the unrequested detail, but I thought it relevant.

To answer your question - there isn't an exact number that is good for every pool, but the recommended range is 30-50 for a manually chlorinated pool, and 70-80 for a SWG. You can play around with these numbers depending on how much sun your pool gets, starting with the low end and seeing how much chlorine is being robbed away by the sun.

 

[Richard320]

Thanks guys.

What I'm trying to figure out, is how then do you decide what CYA level to shoot for? In my case I have CYA at 40, but I'm wondering if there is any advantage to say a level of 30, or maybe even 50?

Yes, there is. I can't use the color-matching chlorine test. Ever. The high Chlorine also tends to bleach out the CH and TA tests. CH in particular never gets blue - more of a no-longer-barely-pink-but-has-a-bluish-tint. And on a more critical note, if I get lax or something and I do get an algae bloom, I'll be looking at adding a heckuva lot more bleach than someone with normal CYA levels.

 

[JasonLion]

Because the CYA test isn't all that precise, you can only target a general range of CYA levels. Generally, it is best to aim for a CYA level of 50 at the start of the season (80 with a SWG) and then hope that it doesn't go down below 30 (60 with a SWG) before the end of the season (it usually won't).

 

[flyboy320]

OK, thanks again guys.

So if my chlorine level falls below the recommended min value (say min value is 3, and I test in the morning and find it's at 2 prior to adding the daily chlorine amount), and the water is still clear, is that a problem?

 

[baudilus]

If it falls during the day it may not be a problem. If it falls overnight it may indicate organics in the pool.

 

[PaulR]

If an overnight test shows things are okay, it just means your daily chlorine amount is too small for that moment of the season. The amount you need will vary with temp, amount of sun, pool usage, pollen count, and other factors. It might average (say) 1.5ppm per day, but that will fluctuate a bit day-to-day.
--paulr

 

[Bama Rambler]

Another reason for not running your CYA at a high level is that if you ever had to shock, your shock level would require an extreme amount of chlorine and be impractical to maintain.

 

[anonapersona]

I think that if you keep records you may find a sweet spot for your CYA. My sweet spot is where I can add one jug of 6% bleach every 2nd or 3rd day. One jug will raise my FC by 4.

 

[flyboy320]

Think I got it now...thanks again...

As a final question, does a CYA level of 40 sound reasonable for my pool (gets direct sun from morning till about 6:00 at night)?

 

[Bama Rambler]

In Canada, yeah, that sounds about right. If you lose more than about 2ppm per day FC you can bump it up a little. It's easier to bump it up than to lower it.