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Salt Water Pools


poolpuppy

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  • 2 weeks later...

When you say that you live in the "tropics", I take that to mean you live in a humid environment. Salt systems work great, as long as excessive evaporation isn't a factor (i.e. you don't live in the hotter areas of Arizona!). In other words, as long as the temps don't consistently go above 100*F and the humidity isn't super low like in Phoenix, AZ, the salt system will serve you well.

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Why is a saltwater chlorine generator (SWG) system a problem in hot dry climates such as Phoenix, Arizona? Yes, there is a lot of water evaporation, but assuming there is an auto-fill or that a solar cover is used, what is the problem that would make the SWG not good while a manually dosed pool would be OK?

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Why is a saltwater chlorine generator (SWG) system a problem in hot dry climates such as Phoenix, Arizona? Yes, there is a lot of water evaporation, but assuming there is an auto-fill or that a solar cover is used, what is the problem that would make the SWG not good while a manually dosed pool would be OK?

The issue would be high hardness level, which would cause scaling in the cell. However, the hardness can be controlled by water softeners.

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  • 1 month later...
Why is a saltwater chlorine generator (SWG) system a problem in hot dry climates such as Phoenix, Arizona? Yes, there is a lot of water evaporation, but assuming there is an auto-fill or that a solar cover is used, what is the problem that would make the SWG not good while a manually dosed pool would be OK?

The issue would be high hardness level, which would cause scaling in the cell. However, the hardness can be controlled by water softeners.

isn't hardness from calcium? I watched a youtube video and they say calcium can build up on the cells and short them out. I guess if cal hypo is used in a SWG pool then the cells split the calcium and chlorine instead of the sodium and chlorine...and thats how the calcium builds up on the cells?

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Water hardness comes from both magnesium and calcium, but it is the calcium that is the issue as it combines with carbonate to form scale (calcium carbonate). This occurs in salt cells at the hydrogen gas generation plate due to the high pH in the region near the plate. However, one can minimize this issue by not over-saturating the water with calcium carbonate -- that is, having the saturation index be less than zero by a small amount. Also, using 50 ppm Borates helps as it provides an additional pH buffer which helps prevent the pH from rising as much near the aforementioned plate.

Sodium and chlorine are not "split" by SWG cells -- that is just a bunch of bunk. Sodium and chloride in sodium chloride salt "split" when added to water -- that is, they dissociate into ions which is why salt dissolves so readily in water. The sodium does not participate at all in the chemistry of the SWG. It is the chloride part of the salt that gets converted into chlorine gas that then dissolves in the water to form hypochlorous acid. At the other plate, hydrogen ions get converted to hydrogen gas. Calcium does not participate in any of this. As noted above, calcium carbonate scale forms because the calcium and carbonate already in the water combine together when the pH rises (assuming the calcium carbonate is near saturation already). They will adhere to any nearby surface and the pH is highest right near the edge of the plate so that's the logical place for scale to form.

If you use Cal-Hypo, then that increases Calcium Hardness (CH) -- specifically increasing calcium ions. If the water is already near-saturation with calcium carbonate (to protect plaster surfaces), then adding more calcium can make it over-saturated and that makes it more likely for scale to form, specifically in the salt cell since the pH is higher at the hydrogen gas generation plate.

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Water hardness comes from both magnesium and calcium, but it is the calcium that is the issue as it combines with carbonate to form scale (calcium carbonate). This occurs in salt cells at the hydrogen gas generation plate due to the high pH in the region near the plate. However, one can minimize this issue by not over-saturating the water with calcium carbonate -- that is, having the saturation index be less than zero by a small amount. Also, using 50 ppm Borates helps as it provides an additional pH buffer which helps prevent the pH from rising as much near the aforementioned plate.

Sodium and chlorine are not "split" by SWG cells -- that is just a bunch of bunk. Sodium and chloride in sodium chloride salt "split" when added to water -- that is, they dissociate into ions which is why salt dissolves so readily in water. The sodium does not participate at all in the chemistry of the SWG. It is the chloride part of the salt that gets converted into chlorine gas that then dissolves in the water to form hypochlorous acid. At the other plate, hydrogen ions get converted to hydrogen gas. Calcium does not participate in any of this. As noted above, calcium carbonate scale forms because the calcium and carbonate already in the water combine together when the pH rises (assuming the calcium carbonate is near saturation already). They will adhere to any nearby surface and the pH is highest right near the edge of the plate so that's the logical place for scale to form.

If you use Cal-Hypo, then that increases Calcium Hardness (CH) -- specifically increasing calcium ions. If the water is already near-saturation with calcium carbonate (to protect plaster surfaces), then adding more calcium can make it over-saturated and that makes it more likely for scale to form, specifically in the salt cell since the pH is higher at the hydrogen gas generation plate.

wow thats plenty info to take in but I sort of understand. will need to bookmark this one as well. I read somewhere that pools were easy to maintain... :rolleyes:

Many thanks for this info. very useful! B)

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  • 1 month later...

These systems work great when maintained properly. We currently only have a handful of clients using them but when they work they are great, when the PCB or Cell decides to die it can be expensive to fix, factor that in the cost when purchasing a salt system. Hey Marc, I couldn't access your blog would love to read more about them.

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  • 4 weeks later...

Hello,

The salt content in a saltwater pool is about the same as the salt content in the human body. It definitely does not harm pool equipment. Here are some of the advantages of having a saltwater pool: No toxic chemicals to buy, store and handle; No stinging eyes and no chlorine smell; Lower maintenance. The main disadvantage of salt water pools is that it reduces the revenue generated by pool chemical sales.

Thanks,

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Hello,

The salt content in a saltwater pool is about the same as the salt content in the human body. It definitely does not harm pool equipment. Here are some of the advantages of having a saltwater pool: No toxic chemicals to buy, store and handle; No stinging eyes and no chlorine smell; Lower maintenance. The main disadvantage of salt water pools is that it reduces the revenue generated by pool chemical sales.

Thanks,

There is a lot that you wrote above that is simply not true. The salinity of most bodily fluids, including human tears, is around 8000-9000 ppm (as shown here, 140 mmol/L * 58.443 g/mole = 8182 mg/L for blood and here, 150 mM/L * 58.443 g/mole = 8766 mg/L for tears) while the salt level in North American saltwater chlorine generator (SWG) pools is around 3000 ppm (in Australia it's around 5000 ppm). The higher salt levels in an SWG pool do reduce osmotic pressure on the eyes, but do not eliminate it. One can also, of course, have increased salt levels without an SWG.

Though the increased salt level does not have to harm pool equipment that is more resistant to corrosion, it is irresponsible to claim that increased salt levels are not more corrosive. The conductivity of the water is roughly proportional to the salt level and increased conductivity increases the rate of metal corrosion generally (the oxidation itself is by chlorine and dissolved oxygen). Specifically, the higher chloride level increases the rate of stainless steel corrosion through interfering with reformation of the passivity layer, though that is a non-linear effect. In particular, this passivity layer destruction effect is very noticeable in aluminum headers in automatic pool covers which are particularly susceptible where you can see this for yourself in aluminum pool cover tracks in this post. Of course, even non-SWG pools have salt, but it takes 2-6 times longer for the splash-out to accumulate the same level of salt.

As disclosed in this EPA report on stainless steel corrosion, "Chlorides present in amounts as little of 0.3% with sulfates present can produce severe corrosion." where I should note that 0.3% chloride is around 5000 ppm salt.

This blog talks about more corrosive aspects of higher salt levels including the effects on steel under diving boards and the effect of splash-out on softer stones.

Any of the problems mentioned above can be mitigated. For example, more corrosion resistant materials can be used including cupro-nickel or titanium heat exchangers in gas heaters. The bonding wire can have a zinc or magnesium anode attached and buried in moist soil, especially if there is aluminum exposed to the saltwater (or splash-out). Soft stones can be sealed, etc. The latter may not be needed in areas where regular rains dilute any splashed-out salt (i.e. it's more of a problem in hot arid areas without summer rains).

As for stinging eyes and chlorine smell, a manually dosed pool doesn't have those problems if the proper FC/CYA ratio is maintained. There are over 20,000 members of The Pool Forum and over 10,000 members of Trouble Free Pool many of whom properly manage their non-SWG manually dosed pools and don't have stinging eyes or chlorine smell or algae growth or other trouble. Of course, many members have SWG pools and love them as well.

Most people buy an SWG system for the convenience. You don't have to add chlorine every day or two as you would without an SWG if you were using chlorinating liquid or bleach. If you have a pool cover, you may be able to add chlorine twice a week. That's what I do in my 16,000 gallon pool shown here and here where I use only 12.5% chlorinating liquid twice a week plus a small amount of acid every month or two -- cost is around $17 per month. So an SWG is not always less expensive when accounting for capital costs. You still need to manage your pool water chemistry in an SWG pool, usually adding some acid to keep the pH lower (though that can be minimized through having a lower TA and use of Borates).

I'm not bashing salt -- I just feel there should be a true balance of pros and cons for any system instead of an "it's perfect" type of sales pitch. Most people are very happy with their SWG pools, but to pretend that there isn't increased risk of corrosion or that some pools haven't had problems would be deceitful.

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For hot tubs, Nexa spa recommends 1500 ppm salt. Not sure about pools, probably the same. I would think damage to be very unlikely at this level,

You are right that the Nexa Spa with instruction manual here only needs 1500 ppm salt, but the Nexa Chlor for Above Ground Pools, with instruction manual here says it needs 2500-3000 ppm salt. Also, keep in mind that even at 3000 ppm, damage is not likely -- it's just more likely and mostly depends on the quality of the pool/spa equipment and fixtures. It's more likely for an inexpensive Intex pool to have a problem and this is exactly what we've seen in some cases where inexpensive screws rusted, but were easily replaced with higher quality stainless steel screws. The problems can be mitigated -- I just don't want people going in without full disclosure.

The higher generating capacity needed for the much larger volume of water in a pool is probably the main reason for the higher required salt level. In a spa, you can get away with much lower efficiency (i.e. more generation of oxygen gas instead of mostly chlorine gas). So you are right that the Nexa Spa should be more reasonable with regard to corrosion rates with only half the conductivity. In the Dichlor-then-bleach method, for people going a while before a water change they might get up to 1500 ppm or even 2000 ppm if they push it, but they start out far lower so the average is lower (more like 700-900 ppm).

There is a new technology being developed that can generate chlorine from very low chloride levels as described in this thread. This will, of course, be the best of both worlds -- automatic chlorine generation with minimal corrosion risk from salt.

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  • 4 weeks later...

<quote>I'm not bashing salt -- I just feel there should be a true balance of pros and cons for any system instead of an "it's perfect" type of sales pitch. Most people are very happy with their SWG pools, but to pretend that there isn't increased risk of corrosion or that some pools haven't had problems would be deceitful. </quote>

That's a really good reply Spa Guru. I did a little post on swimming pool saltwater system trade-off's a few months ago. I agree with your point that we should be talking about some of the less than perfect issues with a salt system as well.

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I worked om a Merchant ship that had a saltwater pool. It was just a sloped steel box in the deck with an inlet line and a drain. It held about 25000 to 30000 gallons. We only used it in the tropics. We filled it directly from the sea, it took an hour to fill using the fire pump. We drained it every other day and didn't add chemicals.

Dave

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I built a pool in San Diego a few years ago and now looking to add a salt generator to my pool. A few friends rave about their salt generators, but are there better options? Leslie's is telling me ozone is a good option and my pool builder likes UV. My pool builder is worried about increasing the total disolved solids with the salt system and says the payback is too long. What do you think? I take care of my pool once a week now, with test strips, but I like the way the salt pool feels.

Thanks!

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My pool builder is worried about increasing the total disolved solids with the salt system ...

The Total Dissolved Solids does not increase very much in a salt water chlorine generator (SWG) system because chloride (salt) becomes chlorine which then becomes chloride (salt) again so there isn't a buildup of salt -- especially if you are able to keep your pH under to control to minimize acid addition (which would otherwise build up salt over time). Perhaps the pool builder was concerned with the absolute level of salt which is high (usually around 3000 ppm) and not really concerned with it increasing over time.

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