Some numbers .. Hardness ?

[chem geek]

Marie,

Well, this is a topic of hot debate as parts of this thread shows. Though the thread was mostly concerning the issue of why a higher CYA level is required for an SWCG system, the answers to that question also relate to why a lower chlorine level may be OK in such a system. Most people find that their CC remains at 0 in an SWCG system and I took a poll recently that showed that this is almost true with manual chlorination though some shocking (1-3 times per season) is typical. At least one user with SWCG reported having algae if not following Ben's table, but most found no problem using a lower amount.

So the jury is still out on this one though I'm leaning towards the belief that the continual shocking of a subset of the water plus fairly even continual chlorine dosing allows one to run at lower FC in an SWCG system.

Richard

[Phillbo]

Maybe I should play with the setting a little to see how much higher I have to set it to increase the chlorine to 5. It's a new system and I have been running it for 8 hours a day (overnight ) at about 30%.

I bought a much bigger cell than needed for my pool so I could run a lower setting . Is there a chart available that shows the increase achieved bases on extended run time or higher cell output ? I'll take a look at the manual when i get home but don't remember seeing anything.

[mbar]

Thanks Richard, I guess that's one good reason for looking at the water clarity. If your water doesn't have any problems, then the lower level is fine, on the other hand if the water isn't clear, then it might be better to raise the chlorine level to see if clears up, even if there is no cc.

[chem geek]

True, but you can't see bacteria! Fortunately, the amount of chlorine needed to kill algae is higher than the level to kill "easy-to-moderate" bugs (bacteria, viruses) up to and including E. coli. So if your pool water isn't developing algae, then it is more likely than not to be sanitized as well, but this obviously isn't a sure bet since you could just be "lucky" about having no algae (algae growth is dependent on other factors such as food sources including nitrates and phophates). At any rate, most users of SWCG systems seem to be operating below the minimums in Ben's chart (they are at around 3 ppm FC at up to 80 ppm CYA which is 0.015 HOCl level) and are still higher than that needed for disinfection (0.011 HOCl level roughly corresponding to 650 mV ORP) and since they are constantly generating chlorine to maintain their level, they are probably safe.

Nevertheless, I would prefer that the SWCG manufacturers design "longer" salt cells (more surface area so generation rates can be lowered per unit area) or change the internal flow rates and geometry so that they could operate efficiently using a lower CYA level (30 would be great, though even 50 would be much better). They will still generate high chlorine levels for their "shock" effect, but the lower rate per unit area will give the chlorine time to combine with the lower amount of CYA at normal flow rates (into and out of the cell, not inside the cell near the plates, where the flow is slowed down intentionally).

Richard

[mbar]

Is there a problem with running a higher chlorine level with a SWG? In my opinion, if there isn't, then why wouldn't you want to be on the safe side and run the chlorine levels according to the "best guess chart"? I don't understand why people are so afraid of chlorine - it has to be in really high levels for it to hurt you, and bacteria are much more harmful. On the other hand if you go by the look of the water, then as soon as it is cloudy, even if there is no cc, then it would make sense that something is wrong, and more chlorine should be added. Most problems I have seen with pools is the lack of adequate chlorine levels. It is really sad that the media (pool companies) have made people so afraid of using too much chlorine.

[Phillbo]

I'm not afraid of chlorine but would like to run my SWCG at the lowest possible setting to maintain a healthy/ clear pool. This will extend the life of the cell and optimize my cost benefit of converting to the system.

My water is crystal clear but I turned the setting up a little on the system to get the chlorine into what is considered optimal around here. It's a new system so I am still dialing it in. If I can get the level up without running above about 60% I'll be happy .. Right now It's set at 45% and the preveiuous numbers posted above were with it set at about 30%.

[chem geek]

Marie,

I agree with you and personally if I had an SWCG I would try to find an optimum "lowest CYA highest FC" combination that I could that wasn't horrible for the life of the SWCG system. Apparently, the salt cell is more efficient at higher CYA of around 60-80 (70-80 is best) for most manufacturers (some say to use a little less) and then the life of the salt cell is based on it's output -- so on longer at higher power degrades the cell faster -- so the life of the cell is dependent on how much chlorine you generate.

Because the loss of chlorine to sunlight is proportional to how much chlorine is in your pool, operating at a higher FC means having the SWCG either on longer or running at higher power or both. At least this is my understanding from others who have an SWCG system. And yes, this is a tradeoff of the "risk" of algae or pathogens vs. salt cell life, though there does seem to be some benefit to the continual dosing and "subset of total water volume" shocking that the SWCG performs so that maybe Ben's chart is too conservative for SWCG systems.

So long as at least 3 ppm of chlorine is maintained, then the pool is at least equivalent to the level of disinfection (650 mV ORP) that is the standard set by WHO and some pool organizations. Wander into this post for more details about ORP and the interesting findings I made from the Oregon Commercial Spas study.

On the other hand, if I had my own SWCG system, I'd probably try to run it at 5 ppm FC (if the CYA were 70-80).

Richard