CYA Question......

[Thegatorvault]

Well, I've been maintaining my new pool since late May, of course with the help of the pool math app and the TF100 test kit. I live in Florida and have a screen enclosure due to mosquitoes and a large oak tree nearby; not saying it's a must here but.....it is!

As expected, with rain and evaporation, my CYA has been dropping over time. With my SWG operating at 70%, my FC was slowly increasing as my CYA went down. Using the TF100 and monitoring, my FC finally got up to 7.5ppm with my CYA at 38. This was surprising and puzzling since I figured the lower CYA would show a reduction in my FC, not an increase. Anyway, I turned my SWG down a few weeks ago to 50% and my FC is now 3.5ppm with CYA at 25. CC has remained consistent at 0.5ppm since the pool has been running. pH is ranging from 7.0 - 8.0 with 3-4 day acid additions by me.

I was wondering if the screen enclosure could be blocking that much UV and therefore a lower CYA amount is ok? I guess it could be a good problem to have but just wanted to be sure the CYA didn't affect anything else other than chlorine breakdown.

I look forward to getting some input on this.......

 

[mknauss]

CYA does not decrease due to evaporation. It does if you had overflow due to rain and it will degrade with high pool water temperatures.

Your UV is reducing right now plus you have the screen enclosure. I would suspect you could lower your FC creation by our SWCG even more if your CYA level was in the 70 range. But that is up to you. I would suggest not going below 40 or 50 CYA.

 

[jblizzle]

Evaporation will not lower the CYA.
CYA is mostly reduced due to physical removing of water (splash out, filter cleaning, leak, etc) it will also slowly be broken down (up to 10ppm / month).

The increase in FC was not due to the lowering of the CYA. The increasing FC was likely due to decrease sun intensity and water temp and perhaps lower usage?

The screen will certainly block some of the UV, but I would think you should need to run the SWG less with higher CYA levels.

 

[YippeeSkippy]

I think that yes, the birdcage does block some UV. More likely your FC demands have diminished as the sun if not as high in the sky, fewer swimmers, etc.

You do tend to lose some when frequent rains cause you to have to drain a bit of water off the pool when it gets too high. This is removing some CYA. There is some normal degradation to the CYA but it is very slow.

Consider your CYA as 40ppm. Treat it as such using the chart--> [FC/CYA][/FC/CYA]

Maddie

 

[Thegatorvault]

Thanks all....yes, slightly mis-spoke (mis-typed) on the evaporation part but thanks for confirmation. Lots of rain lately and overflows, especially with the kids cannon-balling. Agree on the sun intensity as well....still feels like summer here but I guess we are slowly on our way to winter. I'll bump the CYA to 40-50 and see how it goes.

As a side note, I tried to get my 11y/o son to do a science experiment on the effect a screen enclosure has on FC reduction. Unfortunately he wasn't interested.

 

[Pwareing]

Just thought about the sun being less strong - it depends if you are in Northern hemisphere or Southern doesn't it?
The heat may be dropping in the Northern but I think the radiation actually increases?
I think it is due to the sun being nearer to the earth in winter.
Shoot me down if it is rubbish but I seem to remember this from skiing trips.
So is it the heat that degrades the CYA or the UV or a mixture of the two?

 

[mknauss]

Higher water temperature is the primary reason CYA degrades. Elevated FC is also a factor.

 

[Fuldo]

Well, I've been maintaining my new pool since late May, of course with the help of the pool math app and the TF100 test kit. I live in Florida and have a screen enclosure due to mosquitoes and a large oak tree nearby; not saying it's a must here but.....it is!

As expected, with rain and evaporation, my CYA has been dropping over time. With my SWG operating at 70%, my FC was slowly increasing as my CYA went down. Using the TF100 and monitoring, my FC finally got up to 7.5ppm with my CYA at 38. This was surprising and puzzling since I figured the lower CYA would show a reduction in my FC, not an increase. Anyway, I turned my SWG down a few weeks ago to 50% and my FC is now 3.5ppm with CYA at 25. CC has remained consistent at 0.5ppm since the pool has been running. pH is ranging from 7.0 - 8.0 with 3-4 day acid additions by me.

I was wondering if the screen enclosure could be blocking that much UV and therefore a lower CYA amount is ok? I guess it could be a good problem to have but just wanted to be sure the CYA didn't affect anything else other than chlorine breakdown.

I look forward to getting some input on this.......

The screening typically found on Florida screen houses is 18 x 14 x 0.013 fiberglass that is rated at 58% "open". In other words about 58% of the light can come through if the light rays are square to to screening. In practice there is always an angle of incidence and that reduces the transmission even more. That plus the screens get dirty the end result is that less than 50% of sunlight penetrates the screens. You probably have noticed that you never get sunburned in a screened enclosure but try being outside it for four hours or so at mid day, there's a huge difference. I tried to find some formal research and testing on this topic but couldn't after hours of searching. The bottom-line is that much less sunshine gets to your pool when it's in a screened enclosure. However, how much that affects chlorine consumption especially as a function of CYA remains a mystery to me.

I can tell you that my 13,000 gallon pool in the Daytona area is in a screen room and it seems to use much less chlorine than I expected based on other's usage. I get by with about 2 gallons 12% liquid chlorine per week with CYA only about 30. In my case the CYA tends to run between 20 and 40 and I haven't noticed much difference in chlorine consumption within that range. I know that TFP suggests higher levels of CYA but after being burned by excessive CYA earlier and the minimal chlorine consumption I'm seeing I feel like I'm in a good place for this particular pool. I don't know how different a SWG pool like your would be under these circumstances.