CYA for Salt Chlorinator Pools II

[chem geek]

Richard & Poolsean,
The ONE thing that hasn't been addressed in your analysis, Richard, is the fact (using the term loosely) that almost everyone using a SWG with fairly well balanced water reports CC at 0 all the time. This is not true (I believe) of those that use bleach to maintain normal FC, at some point they will get a buildup of CC and have to shock (which is another interesting thread you are involved in!). This would seem to support the idea that the SWG is "super-shocking" in the cell and it must be some larger percentage of the water that passes through the cell than you are calculating.

In thinking about this though, you did say that it might take a couple of days to "shock" all of the water in the pool, perhaps this is happening and is "good enough" to keep the CC reading at or close to zero. I am wondering why or whether this information is available in Austrailia where they have been using these systems for a lot longer than here (at least for non-commercial pools).

A properly maintained outdoor pool using manually dosed chlorine will also report a CC of 0 all the time. If the chlorine level gets too low, then [EDIT]when you later add some more chlorine[END-EDIT] you can build up chloramines, but if it is constantly maintained, then this is much less likely [EDIT]since breakpoint occurs "on the fly" when sufficient chlorine is present[END-EDIT]. Also, outdoor pools exposed to sunlight may have UV breakdown the chloramines [EDIT]and possibly chlorinated organics[END-EDIT]. If you think about it, if you were to manually drip liquid chlorine (remember this is 60,000 ppm chlorine concentration) into your pool near an output jet and did so more or less continuously whenever the pump was running, you are essesntially doing exactly the same thing that the SWG system is doing [EDIT]including exposing some volume of water to very high chlorine levels[END-EDIT]. This implies that for a manually dosed pool it *may* be better to add chlorine in small doses more frequently rather than wait to do it in larger doses every few days [EDIT](and maybe this slower dosing helps keep the CC at 0 by oxidizing CC albeit a small amount of pool water volume at a time).[END-EDIT]

[EDIT]From what I have read, chlorinated organics (aka Disinfection ByProducts or DBPs) are more likely to form at higher chlorine concentrations (which CYA keeps down low) and in particular they form even more when there are chloramines also present so an incomplete breakpoint is the worst situation to be in (i.e. to not have enough chlorine to meet bather loads). The "bad" chlorinated organics, known as THMs, form more at higher pH while at lower pH you get more non-volatile chlorinted organics that are not considered harmful to health, but would still show up in CC if they persisted.[END-EDIT]

To really test your theory, an analysis of indoor pools with and without SWG would be the place to start. Indoor pools have a much harder time avoiding CC since there is no sunlight to break them down nor is there good air circulation to sweep away the products of breakpoint chlorination (though I've never really been convinced that this is an issue since nitrogen and oxygen gasses are already pretty dominant in air so I doubt they get that much higher in concentration above an indoor pool's surface -- perhaps it's other gasses, such as carbon dioxide, that need to be swept away???).

Richard

[chem geek]

Evan (waterbear) also makes good points. If we really want to get to the bottom of this, we would need ALL of the relevant pool water chemistry information that all of you in these forums know is what is asked of you when you want people to help you with your water problems. Of particular relevance for this SWG algae discussion would be minimum FC level, CYA, and pH. The TDS is already roughly known and not a big factor nor is the CH or alkalinity (except that very low alkalinity can lead to large pH swings you might not be aware of) -- I'm not talking about water balance to protect plaster, but rather those components that affect disinfecting chlorine concentration.

Anyway, I don't want to bash SWG systems in any way. Even though I don't have one, I think they are great and the most important service they provide is that they automatically maintain FC levels. And then there's that silky feel of salt water...oooooooo, you've got me thinking about getting an SWG myself!

[waterbear]

Anyway, I don't want to bash SWG systems in any way. Even though I don't have one, I think they are great and the most important service they provide is that they automatically maintain FC levels. And then there's that silky feel of salt water...oooooooo, you've got me thinking about getting an SWG myself!

IF you do you won't reget it! Also, you might be able to clear up some of the issues raised here!

Seriously, IMHO, SWGs are the way to go! Pool maintenance becomes much easier (I only have to worry about keeping a jug or two of acid on hand. Every time I buy bleach for the pool 'just in case' it gets used in the laundry since I don't need it for the pool! I keep an extra bag or two of salt on hand for the water softener and If I need to bump up the salt in the pool a bit I use some of that unless I decide to spluge on bag of Morten or Diamond Crystal pool salt...learned my lesson about off brand pool salt with I got iron stains from one!)