Whats the science behind the SWCG.

[BBBliever]

Ok so I understand how a SWCG works but how is the feel of the chlorine different from basic BBB. I have and AGP that I use daily with my 3 Y/O daughter. I currently maintain with BBB and have salt at 2000 PPM and 60 PPM borates with CYA at 60 for sunny CA. The wife complains that her hair is drying out, which it is. When she uses the pool late afternoon after I am off work the FC is between 5 to 7 PPM.

I just ordered the Intex saltwater system and am hoping it will be a little better on her hair. I though chlorine was chlorine, how dose the chlorine from a SWCG differ from bleach?

 

[bobodaclown]

It really doesn't. That's the simple answer.

If you have a SWCG you can run a lower TC level. See this link:
http://www.troublefreepool.com/pool-school/chlorine_cya_chart_shock

you're Borates levels seems a little high. Usually recommended level is 50.
A little more reading:
pool-school/pool_water_chemistry

But overall this is the section to read:
pool-school/

What's your pools PH? That could be a factor drying out her hair or the high chlorine.

 

[BBBliever]

I test with the taylor kit. Ph is usually around 7.4 never below 7.2. Just used acid aeration to lower my TA from 11O to 80. Maybee a bit more aeration and see how the PH stabilizes.

I went a bit overboard with the borates but I thought anything under 80 ppm was generally acceptable. The 50 ppm limit was established by the EPA for drinking water. My daughter knows not to drink from the pool and the salt helps with that as well.

I guess I will see how the intex swcg effects things.

 

[257WbyMag]

There is no difference between the chlorine that is generated from a SWCG and the chlorine that yields from the addition of bleach.

Pool water is drying to all hair. It is recommended that one shower after swimming to rinse chemicals from the body and hair. She may need to use a conditioner if her hair continues to be dry. It is unlikely that the SWCG will make a difference in the dryness of her hair as it simply produces the same chemicals that one would be adding by hand to a pool without a SWCG.

 

[Bama Rambler]

The only real difference in the water in a swcg pool is you'll have about 1000 ppm more salt in it. the chlorine and everything else is the same.

 

[BBBliever]

I guess I should have knew that what I was reading about the feel of the water with a swcg was good old american marketing.

What I was interested about in the swcg was how you are able to maintain slighly lower levels of FC. It looks like FC levels are 2 ppm lower on the CYA/FC chart with a SWCG.

Anyway I just picked up an Intex 1600 GPH sand filter with the Intex SWCG and a $50 wallmart gift card for $170. At that price I figured I would give the SWCG a try. Thanks for the responses.

 

[frogabog]

TY for the heads up on the walmart deal. Still doesn't make me want to capitalize walmart when I type it though... H can go pick it up.

H is a little worried about the higher flow pump and the existing diameter of the return, being in the flow vs resistance analysis business, that's an issue for him. Our plan at the moment is to replace the over the side pump with the sand filter and leave the 1000gph pump at the skimmer.

Undecided on the SWG. We're happy with BBB, and costing bleach vs SWG (even if you figure $100, a reasonable value if sold on craigslist, right?) we're still going to get two+ years of swimming before it pays for itself. I actually might have to buy CYA if I go SWG, or use some pucks packed in a floater. Salt is how much again?

Bear in mind, H represented one of the first salt water generator/chlorination systems in the late 90's and through early 00's (or near) for municipal drinking water systems. His only concern is cell use/wear/replacement costs which back then were pretty expensive. Paying for the system took longer than the cells lasted which wasn't always cost effective. If we'll have to replace the cell in two years, it's not a good deal anymore.

Any thoughts out there regarding cell life?

As to the title of this thread, SWG science hasn't been explained to me in a long time so I'd be interested if someone knew how it works. I can ask H again, but he'll never come here and type it in so I'd be interpreting it back, likely w/mistakes.

 

[BBBliever]

frogabog, I have seen posts here with people saying there intex swcg is in it 3rd year of service. all depends on useage. I belive even with your 8000 gal pool you could pull close to 3 years. The waranty on the system in 2 years. I think with anything over 5000 gals the salt water system would pay for itself. How much do you spend on bleach a year?

Personaly I would hook the sand filter up to your skimmer. I know people use the 2650 GPH pump with Intex pools and they like it. Wallmart had your pool for sale at $900 and it came standard with the 1600 sand filter.

When my duaghter is big enough I want the 12x24 intex that you have. Maybee a few years, hopefully they will continue to get better and make a thru wall skimmer standard on there pools.

 

[frogabog]

We actually have a 15'x48" Intex metal frame, which according to pool calculator and measuring the water gives me ~4800 gallons. I keep the water a bit low (41-43") which gives us less splash out at 1-4 kids (5-7 however and it's full and splashing!).

Close enough to 5000 gal I suppose. A wash then perhaps.

I go through about a gallon of bleach every week. 128oz is what we're buying from walmart at something like $2.60/bottle (no tax). I am dosing nightly between 2 and 4 cups depending on clouds/swimmers... Not too bad on costs. Pool is open ~June~Sept in a good (read: sunny) year and most of those days are "cloudy no swim" days which give us ~1/4 FC drop instead of 1/2 on sunny days. Overall, BBB is easy and cost effective for us right now. If I sell the SWG for $100, I get the pump and sand filter for $30 which would be cool.

We also don't exactly know how long this pool will last. We might have to replace it in the next two years, who knows? It's a year old now and was not taken down over the winter, it might just fail in the future.

edit: Additional reasoning behind putting the sand filter on the over the side system would be to draw from the bottom with the sand filter, hopefully catching the heavy stuff with it. I'm sure I'll end up using DE too.

 

[chem geek]

The chemistry of a saltwater chlorine generator is described in the latter part of this post. The principle is electrolysis of chloride ion (from salt) in the water to produce chlorine gas that then dissolves to produce hypochorous acid in water. The other plate produces hydrogen gas and lye from water. The net result is the same as adding a hypochlorite source of chlorine (without the extra added salt or sodium). The simplest way to think of this is that the SWCG boosts the energy level of the chloride salt to become chlorine and when this kills pathogens or oxidizes bather waste it gives up its energy and becomes chloride salt again.

I believe most people find SWCG pools to be less harsh because 1) the higher salt levels at 3000 ppm are closer to that in tears at 9000 ppm so there is less pressure on the eye, less skin wrinkling, etc. and 2) the chlorine level can be somewhat lower so will be a little less harsh on skin, swimsuits, hair, etc. However, the greatest contrast is found when looking at pools with no CYA in the water such as most commercial/public indoor pools. Even with an FC of 1 ppm with no CYA, they have nearly 20 times the active chlorine level as an SWCG pool where the FC is around 5% of the CYA level.

 

[BBBliever]

Thank you Chem geek. That explains alot. I'm still curious why the FC levels are 2 ppm lower on the FC/CYA chart with a SWCG. I think I like most will enjoy the SWCG. If not I got it cheap enough that I'm not out much.

 

[chem geek]

The levels on the chart are lower because we have found that SWCG pools are able to prevent algae growth at those lower levels compared to manually-dosed pools. Part of the reason may be due to having the more continuous dosing of an SWCG system and part of it may be the super-chlorination of a portion of the water that goes through the cell. Though manually-dosed and peristaltic pump methods also super-chlorinate some of the water when first introduced (i.e. until more completely diluted), that is at higher pH whereas in the SWCG the chlorine is created and forms hypochlorous acid at very low pH (until mixed with high pH water from the other plate) so is much more active. The proportion of water at this high active chlorine level is fairly low, however, but might be enough to make some difference and of course does nothing to prevent algae growth on pool surfaces (i.e. water not passing through the SWCG cell).

 

[UPSguy]

Even with an FC of 1 ppm with no CYA, they have nearly 20 times the active chlorine level as an SWCG pool where the FC is around 5% of the CYA level.

I really don't belong in the deep end and I am sure you have gone into great detail on this already. Also, I am not doubting you at all but this leads me to 2 questions.

1) Could you please tell me how you figured this out?
2) Why use the CYA then?

If I may be allowed to offer a little history. We got our 1st Intex pool July 09, it came with the combined pump/SWG. The owners manual never brought up needing CYA (unless I missed it) so we never used any, never did a good water test but somehow through dumb luck or devine Providence had sparkling clear water that everyone who got in the pool raved about. It wasn't until this Mar when we ordered the bigger intex and bought the new SWG that I noticed there was a difference. The old one made 24 grams/hr of CL and the new one with the stinking copper only makes 12 gr/hr. It was studying the differences that somehow led me to this GREAT forum and showed me how stupid I am about pools.

Heck we never added any start up chemicals, just ran the SWG 5 hours a day. Actually started out at the recommended 4 hours from the owners manual but when the wall got a little slick I upped the time to 5 hours and brushed the floor and walls. That is all we ever did. Like I said, blessed or lucky???

Now with the new one making less CL and telling you how much CYA to add, plus reading your post about how much more effective a small amount of CL is without CYA has me scratching my head as to why we need it?

If you can clear this up for me I'll be a greatful beginner.

 

[JasonLion]

1) Trial and error.
2) Without CYA you lose all of your chlorine to sunlight very very quickly.

I suspect your pool might have had CYA in it, even though you didn't intentionally add any.

 

[chem geek]

CYA is needed not only to protect chlorine from breakdown from sunlight, but at usual FC levels the active chlorine level is too strong if there is no CYA in the water. Most pathogens are very easy to kill with very low active chlorine levels. It's algae that is generally harder to kill and is the basis for the Chlorine / CYA Chart. Though you don't need any more than 0.1 ppm FC with no CYA in the water to prevent algae from growing, it is impractical to try and maintain such a low chlorine level. Having CYA in the water lets you have a higher FC level so there is more in reserve so you don't run out even under local bather load or other demand while simultaneously having a lower active chlorine level so that it isn't as harsh on swimsuits, skin, hair, nor in creation of disinfection by-products. CYA in the water is like having an automatic chlorine feeder everywhere in the pool adding more active chlorine as soon as it gets used up. Of course, usually over a day or two, the FC reserve drops enough that you need to add more either manually or through automatic systems such as The Liquidator or a peristaltic pump or a saltwater chlorine generator.

As for the estimate of the amount of active chlorine (hypochlorous acid) in the water at FC/CYA levels, it is roughly proportional to the FC/CYA ratio and this is derived in this post. The accurate calculations based on known equilibrium chemistry are in the spreadsheet linked to at the end of that post. The levels that prevent algae growth were initially determined by Ben Powell through observation of pools at various levels and trial-and-error (as Jason noted). These levels are for preventing algae growth using chlorine alone with no algaecides or phosphate removers or weekly shocking.

 

[teapot]

As it is the deep end.

I have been experimenting with a CYA replacement in my pool that allows me to run FC at 0.2 (No CYA) The formular is based on Titanium dioxide nano particles (sun screen) which also increase the redox potential of the water and all surfaces in contact with the water so they become self sterilising under the suns UV. The only real problem is its a regular addition not a one time like CYA but the lower chlorine usage and acid should hopefully negate this extra cost.

The trials continue.......

 

[UPSguy]

Thank you Chem Geek, and Jason. I purposely didn't read this while driving down the road on my blackberry so I could digest it when I got home. Almost wish I would have to see the original draft before the edits.

This CYA thing really has my interest peaked since we ran without any for 2 summers. If intex's specs are correct we put 120grams of CL in 6900 gallons every day.

 

[chem geek]

If intex's specs are correct we put 120grams of CL in 6900 gallons every day.

If that is a 24-hour rate and your pump and SWCG were running for 24 hours at 100% on-time, then that would be 4.6 ppm FC. You could certainly operate a pool without CYA with that amount of chlorine generation, but the average FC level would have to be low since about half of the FC is lost in one hour in direct noontime sun if there is no CYA in the water. If we figure the equivalent of 8 hours of loss at this rate (say, a 12-14 hour day, but obviously not all noontime sun), then we have FC/2 = 4.6/24 so FC = 0.4 ppm and technically you wouldn't have to run the SWCG very long outside the daytime hours. Since you only need somewhat less than 0.1 ppm FC with no CYA to prevent algae growth, this method can work if there isn't any extra chlorine demand.

You said you ran the SWCG for only 5 hours each day so you were certainly lucky to not get algae. Most likely, your fill water was very low in algae nutrients (phosphates and/or nitrates) or you got lucky not to have any algal spores get blown in. So long as the SWCG wasn't fighting nascent algae growth, it was probably able to keep up with chlorine breakdown from sunlight, albeit at low FC levels, but without CYA in the water that was OK. The problem is that any nascent algae growth or usage of chlorine from bather load could wipe out the FC to an even lower level or close to zero and that's when algae can take hold. Once that happens, the SWCG would not be able to keep up.

Note that if you used ANY Dichlor or Trichlor in the pool, then you would have had some CYA in the water. If you started with a fresh fill and only used the SWCG (or unstablized chlorine), then there would be no CYA in the water.

 

[chem geek]

Pool water is drying to all hair. It is recommended that one shower after swimming to rinse chemicals from the body and hair. She may need to use a conditioner if her hair continues to be dry. It is unlikely that the SWCG will make a difference in the dryness of her hair as it simply produces the same chemicals that one would be adding by hand to a pool without a SWCG.

Just wanted to make a comment on this. The somewhat lower active chlorine level in an SWCG pool might make some slight noticeable difference in the drying/frizzing effect on hair. However, it's mostly the chlorine in the water that has this effect on hair. Even at the relatively low active chlorine levels we recommend, the chlorine still oxidizes skin and hair, albeit much more slowly than in a typical indoor pool with no CYA.

Of course, even showering with chlorinated water will have this effect (note that some water systems now use monochloramine instead of chlorine and will have a different, possibly less harsh, effect). Of course, if you swim a lot the amount of time your hair is exposed to shower water is usually a lot less than the time it is exposed to pool water (especially the ends for long hair). My wife swims every day in our pool so to minimize the effects she uses a cap during swimming (but not during the longer therapy exercises), showers afterwards and uses a shampoo with reducing agents that dechlorinate and also help to recondition the hair. She also thoroughly towel dries her hair right after showering. This combination seems to work well. When she uses the indoor community center pool that doesn't use CYA, the effects are far more noticeable and the showering/shampooing isn't enough to eliminate damage from her hair. Of course, while in such a pool the chlorine is attacking her hair 10-20 times faster than in our own pool and while a swim cap helps, some hair gets exposed nevertheless.

Those that promote chlorine-free pools are correct in their claims on having less effects on skin and hair. You still end up with wrinkled skin unless the salt levels are higher, but the hair is not affected as much. If there were a way to selectively kill pathogens and prevent algae growth without affecting skin and hair, then that would be ideal, but all such approaches have extra costs, side effects, or are not as sanitary. Nevertheless, one can minimize the active chlorine level in a residential pool and use other techniques to prevent algae growth. For example, Polyquat algaecide added weekly would probably let one have at least half the chlorine level if not somewhat lower and if combined with borates possibly even lower than that. Phosphate removers could also work if their were not a lot of organic phosphates. Copper isn't a good solution not only because of the potential for staining unless the pH is kept low and levels carefully controlled, but copper affects hair directly since it is absorbed into the hair and when forming oxides turns green (ironically, most shampoo is higher in pH and can accelerate this process when copper is present). I don't know of the effects (if any) of Polyquat or borates on hair.

 

[UPSguy]

I used straight city water for fill that 2 seasons, nothing else ever got added. At 4 hours I did notice a little slickness starting on the walls. I brushed them and upped the time to 5 hours and never had a trace of slickness after that. I was (still am but learning) a complete pool idiot but amazingly everybody that got in the pool commented how nice and clear the water was and were absolutely shocked when I told them I did nothing but run the SWG 5 hours a day.

Thank you very much for taking the time to explain this to me, I greatly appreciate it. Although, pool care was a lot easier as a very lucky idiot.