Some numbers .. Hardness ?

[Phillbo]

Is the hardness number an issue?

Temp 85
CYA 65 -76 ( depending on the test,it appears to vary)
TC 3.6
FC 3
pH 7.5
TA 95
Hardness 407
salt 3400

I added a little acid after the test. Shoudl I add something for the Alk? We had a storm last night that added about an inch of rain water.


Pool is crystal clear and no growths.

Other than the hardness, I think all I need to add is women and beer ;)



can you edit titles ? sloppy typist here !!!!

[chem geek]

Your numbers are near perfect (LSI is 0.01 and my improved CSI is -0.11) and for calcium (CH) and carbonate (TA adjusted with CYA) water balance you get a lot of leeway before you run into trouble (some cloudiness has been reported at CSI of +0.75 so that gives you an idea of how far out of balance you have to get to start seeing any problems).

It is interesting that with your SWG system you are reporting a CC=TC-FC=0.6 since nearly everyone that has an SWG system reports CC=0 all the time. If you trust your test kit, you might want to try shocking your pool with extra liquid chlorine (or bleach), but it's hard to prioritize that against women and beer.:) You could probably just wait to see if your SWG gets the CC down to 0 (TC=FC) naturally.

Richard

P.S.
If you click on the "Edit" button and then click on "Go Advanced", then you can edit the title as I did in this post.

[Phillbo]

Should I try to do anything about the hardness?

[chem geek]

Sorry, when I said that your water balance was near perfect, that means that your hardness (CH) is fine and you can leave it where it is. Also, I wouldn't worry about the alkalinity (TA) either. If you find that you have an upward pH drift over time and need to add acid regularly, then you can consider lowering your TA; otherwise, leave things as they are.

Richard

[mbar]

When you have a SWG, do you not have to keep the minimum chlorine the same as when you don't? The chlorine level of 3.6 is not high enough with a cya of 65 - 76. The minimum should be 5, max 10 and shock 20. THis could be why there is cc of .6

[chem geek]

Marie,

Well, this is a topic of hot debate as parts of this thread (http://www.poolforum.com/pf2/showthread.php?t=4495) 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 (http://www.poolforum.com/pf2/showpost.php?p=32228&postcount=16) 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

[Phillbo]

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).




Thats my plan.

[mbar]

Ok, I get that, but if you put enough chlorine in manually, then the cell wouldn't have to generate as much....or am I just not getting it? So if you started out with 5ppms, and your cell was just making free chlorine as needed, then wouldn't it make enough fc to keep the level up to 5? Or is that what you mean 30% - 45% is? As you can see I don't have a SWG.

[Phillbo]

The reference to the 30- 45% is the setting on the SWG. It means that when it's running, it only produces chlorine XX% of the time. The more it runs, the more chlorine it produces.. so, there should be that magic % that produces just enough without burning the cell up too fast.

[chem geek]

Phillbo is correct, but perhaps looking at this graph (http://richardfalk.home.comcast.net/pool/HalfLife.gif) may help. At any given level of CYA and FC, there is an amount of time it takes for half of the total chlorine to breakdown from sunlight (UV). You can see that the curves get close together at higher CYA which means that the half-life of chlorine is independent of the amount of chlorine. The half-life is the amount of time it takes for half of the chlorine to breakdown so if you have more chlorine in the pool, then more gets broken down and has to be replaced (because "half" of a larger number is bigger than "half" of a smaller number).

So if you try to maintain your pool at 5 ppm of chlorine instead of 3 ppm, you will lose up to 5/3 = 1.67 or 67% more chlorine per day and will have to make up for that somehow. In an SWCG system, you would turn up the percentage of time that the system operates -- namely 67% higher.

Now in addition to chlorine usage from the breakdown from sunlight, chlorine also gets used up by combining with and oxidizing organics and disinfecting pathogens (bacteria, viruses) and killing algae. This usage is dependent on how much of this stuff is in your pool and is therefore independent on the amount of chlorine in your pool.

You can distinguish between these two types of chlorine usage by seeing the usage overnight when the sun doesn't shine and compare this to the usage during the day. If you subtract your overnight "per hour" usage from your daytime "per hour" usage, the difference will be the loss from sunlight.

Typically, the usage (independent of chlorine level) oxidizing and disinfecting is pretty small, usually less than 0.5/day while the usage (dependent on chlorine level) from breakdown from sunlight is quite high with about half of the chlorine lost during the day (this varies a lot depending on the amount of sun exposure, latitude, etc.). So with this example, maintaining a 3 ppm FC would require generation of 0.5 + 3/2 = 2.0 ppm per day while maintaining a 5 ppm FC would require generation of 0.5 + 5/2 = 3.0 ppm per day. So in this case the increase in the salt cell is 50% (so if currently running at 35%, you would need to increase this to 35% * 1.5 = 52.5% (so 50%).

Richard

[Phillbo]

now my head hurts :eek:

[Watermom]

Maybe if the spelling in your thread title is fixed, it will make your head feel better! ;)

(I fixed it for you.)

[Phillbo]

Talk about twilight zone... I thought I did fix that after someone told me to go to the advanced section.... Thanks.


I upped the setting just a bit ( about 40% on the dial) since I don't want to run the pump longer due to the pool staying clean at 7 hours a night. I retested after a few days and my FC is now at 4. I think I will leave it like that for a while and see how it does. It's a little low on the "best guess" chart but I thinkk it's fine since my CYA may be a little lower then reported. I find the test to have a little variance.

[Watermom]

Talk about twilight zone... I thought I did fix that after someone told me to go to the advanced section.... Thanks.




You can edit a post you have made and the title within that post, but to be able to edit a thread title itself is an administrative function that only Ben and the moderators have access to.