Hot climates = option of high CYA?

[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.

[smileitsachoice]

Thanks for the reply. I had to drain about 10000 gal out because I had been pool stored(triclor and diclor). My cya was over a hundred and I had algea I could not get rid of. Since I have been on the BBB method all I do is add 1 jug of bleach a night and brush once a week. I did add 320 lbs of salt. I purchased some salt strips and tested. Took my salt to 1650 ppm. This really seems to help the comfort factor. My pool is the cleanest it has ever been, and upkeep has been very easy.

[Furbabyvet]

dhanger:
I'm also in Phoenix and still working on straightening out a pool I had royally messed up by following pool store advice. My CYA was over 250 a couple months ago. After partial water changes, we got it down around 30-40. I am currently losing 2.5-3.5 ppm of FC during most days. I'm using just a couple of trichlor pucks at a time to slowly increase my CYA, but not sure what my goal is. Not >250, though, that's for sure.

I did just add borax to 40 ppm and may be seeing a slightly decreased FC demand. I am going to start putting our solar cover on the pool to conserve FC, though not sure I can stand to swim in 95 degree water . If the FC demand goes down significantly, I will go buy a solid colored cover. I'd love to avoid worrying about algae and adding LC every day! SWCG is not in our budget this year.