So how come there aren't a LOT of sick people?

[bbb]

Actually you need more! The cell instantaneously generates a high concentration of chlorine that destroys the chloramines AT the cell.

If there was not a high CYA level, most of it would be used up before it got into the pool proper. The alternative would be to run at high chlorinating outputs, resulting in rapid reduction of cell life.

Hope this helps.

Pat

:lightbulb lighting over head:

Thanks, Pat. This is about the 10th time I read that if there was not a high CYA level, most of the SWG-produced chlorine in the cell would be used up before it got into the pool proper - and I finally figured it out -

Without the added CYA, the superchlorination at the cell is TOO effective, so, under higher bather load or organic contaminant conditions, there isn't much unused FC left after the water passes the cell and goes toward your return!

With additional CYA present (say 60-80 ppm), there is a little less superchlorination at the cell (because chlorine is less effective per PPM with CYA present), so there is more residual left as the chlorine passes back into the water into your pool, where it can fight contamination of the water actually in the pool and (keeping this sort of on topic), preventing people from getting sick from stuff in the pool!

Finally, because there is still effective (just a little less powerful per PPM because of the 60-80 ppm CYA) superchlorination going on in your water because the salt water generator cell is operating, you should be able to run with a (slightly) lower amount of FC residual in your SWG pool than with a pool chlorinated in batch form (like bleach or cal-hypo) or drip form (chlorine feeders, trichlor pucks) for your given level of CYA.



ps - the "benefactor or bomb" article is very good but needs to be taken with a grain of salt (whether or not you are running a SWG! ) PoolDoc has excellent comments elsewhere on the forum about it - here is the link. CYA is NOT "bad" -- running your pool with too much of it and not enough chlorine (like anyone using a constant amount of trichlor pucks in a feeder all year, and using a test kit or strip that only counts to 5 or 10ppm of chlorine) IS "bad". It's that simple. And for people who have very sunny pools (aylad comes to mind), CYA is a huge help. My pool isn't that sunny, but when I cholorinated exclusively with bleach last year, I chose a higher CYA rate so I could add bleach every other day instead of every day. And now that I have an SWG, I am slowly increasing my CYA from 35 to (probably) around 60.

My understanding: with the addition of common sense and real-world experience to the "benefactor or bomb" material, you get Ben's "Best Guess" chart.

[Tredge]

PoolDoc has excellent comments elsewhere on the forum about it - here is the link.

Thanks for linking that. Ben does an excellent job as usual responding to that article.

The folks in this forum are really impressive.

[waterbear]

Been following this thread and need to add a few comments. The following gets somewhat technical so you have been warned!
1. When the article on CYA is talking about automatic delivery of chlorine it is NOT talking about a SWG. It is talking about using a peristataltic pump and an ORP controller to automate the addition of liquid chlorine to a pool to maintain a certain redox potential...apples and oranges, not the same thing at all.
2. the author of this article was/is connected with a company that manufactures ORP controllers for pool and CYA messes up ORP readings. ORP controllers work best when there is no CYA present by constantly dosing the water with chlorine as it is demanded by use.
3. Let's examine a quote from the article (with empahsis added by me):
"An ORP level in water of 650
mV is the most widely accepted minimum for qualitative
results, worldwide.
650 mV of ORP can be achieved with a variety of
chemical compounds, conditions, and influences. It is “qualitative”.
650 mV is the same working value whether it takes only
.1 ppm “free” chlorine at pH 7.2 with no CYA to get there or 3
ppm at pH 8 in the presence of 30 ppm CYA to make it. In the
second of these two extreme examples it takes 30 times more
chlorine to achieve the same results. All it took was a pH elevation
and the addition of cyanuric acid."

when sodium hypochlorite is added to water it dissociates into hypochlorous acid and hypochlorite ions. Hypochlorous acid is what has the oxidizing ability...hypochlorite ions do not. The ratio of hypochlorous acid to hypochlorite ions is pH dependant. At a pH of 7.2 over 75% of the chlorine is in the form of hypochlorous acid so the oxidative ability is very high!
At a pH of 8 less than 20% of the chlorine is in the form of hypochlorous acid. It is a given that the addtion of cya will have an effect on lowering the oxidative ability somewhat since chloroisocyanurates are less potent oxidizers than hypochlorous acid. However I submit that it is the change in pH that has the most impact on this example. The differential in oxidative ablilty with just a change in pH is over 55% for a given level of residual chlorine! IF my math is correct it would take over 1.8 ppm FC at pH 8 with NO CYA to achieve the same results as .1 ppm at pH of 7.2. The addition of 30 ppm CYA only affected the results by slightly over 1 ppm (about 35% more needed) while the change in pH needed about 170% more chlorine for the same oxidative ability when no CYA is present!
Which is the parameter that has the greatest impact here....pH or CYA? I submit it is the pH!
4. The author states at the end of the artice
"This writer has, by the way, used cyanuric acid successfully
and with benefit in his own pool for years."
This certainly sounds like an endorsement for using CYA to me!