Hot climates = option of high CYA?

[joecus]

Yup, that's me! Still down here, oil slick or not

Janet

Hi Janet - I read this quote and wanted to ask you why a high cya is important to a pool that gets a lot of sunlight. That is the case with me. Also, I assume I could use the "shot glass" method to test my cya, is that correct?

[waterbear]

Hi Janet - I read this quote and wanted to ask you why a high cya is important to a pool that gets a lot of sunlight. That is the case with me. Also, I assume I could use the "shot glass" method to test my cya, is that correct?

Higher CYA can protect against loss from sunlight but you need to run the FC higher to compensate for the chlorine that becomes chemically bound to the CYA in the water and is not available as a sanitizer. Net effect in some pool is lower overall chlorine usage and in many cases chlorine does not need to be added daily to maintenance becomes less. However, all pool are differnt so YMMV.
As far as 'shot glass method' for cya, yes but it is only really useful if your CYA is testing at 100 ppm to see how MUCH over 100 ppm you are.

Since you are the third poster to post a pool problem in this thread perhaps the MODs would be kind enough to break it off into it's own thead or combine it with one of your other theads to avoid confusion!

[dhanger]

That brings up a question I've wondered about since I first started using the K2006 test kit, I've read the book that came with it from cover to cover like it was a bestseller (I'm an invertebrate, er, inveterate manual reader) and it's gratifying to see how closely the information in it correlates with most of the info here on the forum, however, on page 26, under 'Chlorine Stabilization' it states that "Above 50 ppm, only marginal stabilization benefit is observed." Some people here have said that they keep their cya much higher when they have high sun exposure. My cya level is about 45, with sun exposure at least 8 hours in summer, and I typically lose about 2.5-3.5 ppm of FC. My question then is, is that amount of loss considered high, and do people see more than 'marginal' benefit from much higher cya? I'm probably being overly analytic, but that's my nature.

Dan

[lbridges]

I have a relatively new pool (a little over two months of water). During the second month a Pentair IC-40 SWG unit was started up. Due to a miscomminication between the equipment setup guy and the company pool service the filter was cleaned not long after CYA was added. As a result the first 10 days or so I had a CYA level of about 40. The SWG had to be run at a 60% duty cycle to keep FC at the target level (set for a CYA of 70). After correcting the CYA level to 70, I have been able to turn down the IC-40 duty cycle to 25%.

This is for a pool receiving direct sunlight from dawn to dusk, space coast area of Florida.

[CarlD]

There's some discussion as to whether or not CYA levels that are higher provide any benefit. The answers seem to be:

1) If you have a SWCG, then the higher levels are mandatory (around 70) both for the correct functioning and to avoid voiding your warranty.

2) In extremely hot, muggy, sunny climes (like Louisiana) people find they just cannot keep chlorine levels consistent without higher CYA levels. Our La. Mod, aylad, finds she must always keep her pool at 70-80ppm of CYA or she cannot maintain her residual chlorine. Real experience trumps theory in this case.

In our extreme heat, here in NJ, where it's been in triple digits in both temperature and humidity (105 F and 100% humidity), despite my CYA of 50, I've been having to add LC every day.

3) It seems that if you cannot maintain a steady residual FC level, you must increase your CYA and target your residual level accordingly.

Hope this helps.

[dhanger]

CarlD-

As is sometimes the case, I know it's true that theory and practice don't always see eye to eye. Not ever having been around SWCG's I wasn't even aware of the need for higher cya for those. Interesting. It sounds as though you might be saying that higher humidity may be a factor (105 F. with 100% humidity! I salute you). Here in Phoenix we have the same temps throughout the summer, but very low humidity except for a short monsoon season, yet I have the losses I mentioned, so it doesn't seem to my mind that there is a connection with humidity. You didn't say whether the loss I am experiencing is high, low, or normal, but when you say "I've been having to add LC every day", it sounds as though it should be normal experience to maintain a steady reading for extended periods, at least longer than a day. What exactly does it mean to "maintain a steady residual FC level"? This is all fairly new to me (I've been terribly ignorant in my 5 years of pool ownership), so I'm still working on sorting out what should be normal.

Thanks,
Dan

[chem geek]

Mark (mas985) did an experiment described in this post that showed that a higher CYA level protects chlorine loss from sunlight in a non-linear way that more than makes up for the greater loss from proportionately raising the FC level to keep the FC/CYA level constant. We still don't know exactly how this works though my best guess is the CYA shielding effect of lower depths since that would be a non-linear effect if there was not perfect mixing from surface to depth. This effect has been seen in many pools, but not every pool. The Taylor book is wrong on this (it's a good book, but it's wrong on other issues as well and has no discussion of the chlorine/CYA relationship).

So having a higher CYA isn't something special for SWCG pools and can be done with any pool that has a lot of loss of chlorine from sunlight. However, there are reasons why it makes more sense to have the higher CYA with SWG pools since the SWCG maintains a more constant chlorine level where the risk of having the chlorine too low is lower since you don't "forget" to add chlorine. If you let the FC get too low at a higher CYA level, it takes a lot of chlorine to shock the pool so it's more difficult to control. Also, most SWCG pools rise in pH and one of the ways to lower that is to lower the SWCG on-time so lowering the chlorine loss due to sunlight is a way of doing that. Finally, it seems that SWCG pools can operate without algae by maintaining an FC that is roughly 5% of the CYA level which is lower than the minimum FC in manually dosed pools (i.e. 3 ppm FC with 60 ppm CYA or 4 ppm FC with 80 ppm CYA compared to 5 ppm FC).

Richard

[CarlD]

I don't know if humidity has a direct effect but it may well have an indirect effect as hot, humid climates are obviously more hospitable to all sorts of plant growth, from microbes to palm trees, than hot, arid climates. Add that to increased and more direct sunlight and it seems that conditions to deplete chlorine would be ideal.

If you look at the famous "Best Guess Table" you'll see that for various levels of CYA, there are recommended maintenance levels for your FC and recommended shock levels.

At higher CYA levels, once you establish that maintenance FC level, it should be easier to sustain. The explanation and chemistry of how much chlorine is "bound up" with the CYA and yet how it maintains its levels and protection is beyond me.

CYA is a two-edged sword, but if you follow the "Best Guess" table it's easy to maintain a sanitary pool at most CYA levels. Denizens of the South and South East, where summers are really hot and muggy with more intense sun than, say NJ (where we are 100+ hot and muggy right now!) may find, like aylad, that higher CYA levels work for them.

[smileitsachoice]

My question is like dhanger. I have a inground vinyl pool at 30000 gallons. I live in hot and humid Alabama with my pool getting full sun all day. My chem numbers the last 2 to 3 weeks have been very stable. cya at 65-75, ph 7.7, cc 0. My fc is as follows: when tested at night it is 6 to 6.5, I add 182 oz 6% bleach every night. My fc in the morning is always 8.5 to 9.0. Does this seems right. My water is very clear. i have not vac. or backwashed in 3 weeks. I thought this was just average fc usage. fc stays the same with pretty much a small or big bather load.

[CarlD]

That sounds right....
You test at night and your FC is 6ppm or so. You add 182oz of 6% to 30000 gallons, which adds 3.34ppm of FC. Some is consumed overnight and you wake up to around 9ppm...in the morning.

Makes sense to me.