Swimming Pool Salt Water Chlorine Generator FAQ

What is a salt water system?
A salt water system or “salt water chlorine generator” (SWCG, SWG) is used to replace traditional chlorine with chlorine produced from salt in the pool water.

How does it work?
Salt, or sodium chloride, dissolves in water separating into sodium (ions) and chloride (ions). By passing a low voltage electrical current between special metal and through the water, the SWCG then converts the chloride into chlorine in a process called electrolysis.

The newly created chlorine creates a chlorine residual, and is available to sanitize the pool. When it is used up, it changes back to chloride, and allowing the process to start over again.

So a pool with an SWCG is not chlorine free?
Correct! An SWCG is just another way of adding chlorine to your pool. It's a good way of doing so, but the end result is still a chlorinated pool. You must test and maintain chlorine levels just as you would on any other chlorinated pool.

Why are you calling it an SWCG (Salt Water Chlorine Generator)?
There are at least 3 other abbreviations in use: SWG, SCG, SG, and so on. SWG, Salt Water Generator, is simply inaccurate. An SWCG doesn't generate salt -- it has to be added by hand -- and even if it did, generating salt wouldn't sanitize your pool. (Salt is NOT a sanitizer!) SG, Salt Generator, is worse than SWG for the same reasons. SCG, Salt Chlorine Generator, is somewhat more accurate, but confusing and not as common as SWG. SWCG is accurate and descriptive, and is similar enough to SWG that many people will be able to recognize it easily.

Doesn’t the salt in the water alone help control algae?
No! Salt alone is neither an algaecide (kills algae) nor a sanitizer (kills germs). As in other pools, it is the chlorine produced by the SWCG that kills both algae and germs.

What size of SWG should I buy?
Too large is usually better than too small . . . if the unit can be turned down. SWCG cell life is a function of hours of 'on-time'. A unit with 2x the chlorine output of a smaller one, will tend to last 2x as long on particular pool as the smaller one, but will not (usually) cost 2x as much.

Sizing recommendations from the manufacturers are not standardized, however. The only way to compare units from different manufacturers is if they give a "pounds of chlorine gas equivalent per day (or week)" rating.

I've got an indoor pool. Does that change things?
Yes! An outdoor pool typically loses over 80% of its chlorine to sunlight. This means an indoor pool with the same use levels, will need less than 20% of the chlorine an outdoor pool does. In most cases, if you have an indoor pool, you'll want the smallest generator available. Otherwise, you simply won't be able to turn it down enough.

How much salt do I need?
This depends on two factors, the size of your pool and the recommended salt level according to the manufacturer of your SWCG.  A general rule of thumb is 50 lbs. of salt for every 2000 gallons of water.  So as a simple guideline, a 12,000 gallon pool would need approximately 300 lbs. of salt.  This is only for estimating purposes; you should follow the recommendations of your SWCG's manufacturer.

That seems like an awful lot of salt, won’t that make people sick?
The salt level in the oceans of the world is 35,000 ppm; most salt systems require approximately 10% of what is in the ocean, usually between 3000 – 4000 ppm to operate efficiently. This is enough to give the water a slightly salty taste, and a slightly different 'feel', but that's all. Many people won't notice; almost everyone adjusts quickly. To get a rough idea, a salt concentration of 3600 ppm of salt is approximately 1 tablespoon of salt in a gallon of water. In comparison, seawater would have approximately 9 to 10 tablespoons per gallon.

By the way, because the water will be slightly closer to the salinity of human tears, the water will be less irritating to people's eyes. Many pool users don't know this, but fresh water, even if completely free of all germs AND all pool chemicals, is irritating to human eyes because of the LACK of salt in the water. Sea water has MORE salt than tears do, so it's irritating in the opposite way.

So you're saying a pool with an SWCG will irritate swimmers' eyes LESS?
Yep. The human tear has approximately 9000 ppm of salt. Because, saltwater pools are closer in salinity to the eye’s natural levels, they tend to irritate eyes LESS than other pools. (For those of you who are technically oriented, the pool water in an SWCG treated pool has an osmotic pressure closer to that in the eyes, than a fresh water pool.)

What about people with medical conditions who have heart or skin problems, or who are on a low-sodium diet, etc.?
We discussed this one. None of us have found any medical literature, one way or the other. If salt water caused problems, you'd expect that there would be cautions to such people about swimming in the ocean (which is much saltier), and we didn't find THOSE either.

The consensus (and we are not doctors, lawyers, accountants or government bureaucrats!) is that any effect would be small, and if anything would be likely to help.

Caution language like this tends to be lawyer-driven language which is designed to maximize coverage of the gluteus maximus of all involved parties. This language is typically is uninformed, meaningless and incomprehensible.

Where do you put the salt?
With most modern SWCG's, you add the salt directly to the pool, where it dissolves and disappears very quickly.

What kind of salt should I use?
Ideally, any non-iodized salt pure enough to eat, is pure enough for your pool. As always, the pool chemical companies are trying to add their own special ingredients to the salt. And as always, you're better off with just plain salt.

Some grades of salt for water softeners may have additives designed to help the zeolite beads in softeners. Since just what these additives are is unknown, it would be safer to avoid using those grades of salt.  Your SWCG instruction manual should include salt requirements.

Is the salt expensive?
A 40 lb. bag of pool salt will cost between $5- $10 per bag depending upon your location, and is available at most hardware stores and some grocery stores. At $7 per 40#, adding salt to a 24,000 gallon 18 x 32 liner pool would require about 18 bags, and cost about $125. At 700#, that's too much weight for the trunk of your car, however. So make more than one trip, if you don't have a truck!

Do I just dump all the salt in at once? 
NO! You should determine the amount of salt you need, and then add about a half of it and let it dissolve. Then, either test or have the salt level tested. Complete the process by adding 1/4 doses (1/2 of the remaining salt) slowly until the required level of salt is reached.  Overfilling or exceeding the maximum salt levels required by your SWCG can result in draining a portion of the pool water and re-filling with fresh water. Most pool stores will test your salinity level for free.

Am I trading bags and bags of salt for chlorine tablets or bottles of chlorine?

You do have to add salt, instead of chlorine, but after the initial fill of salt, little additional salt is needed to maintain the proper salt level of the pool. If you use a cartridge or DE filter, you may only need one 40lb. bag of salt per season. Due to water loss from backwashing, you may need more salt if you have a sand filter.

I thought salt water is very corrosive. Will salt water damage my pump, pool heater, solar unit, and so on?
 It depends.

Some pool heaters, including most older heaters, are not compatible with salt use. Certain unusual types of corrosion are worsened by salt’s presence. But generally using salt is not a problem for most vinyl or concrete pools.

What seems to be the case is that if your pool is made with materials that already tend to corrode, salt will make it worse. But, for owners of vinyl liner pools with plastic pipes and plastic pumps . . . adding salt shouldn't be an issue. Owners of older concrete pools may want to ask the installer if he will refund the unit if new corrosion occurs. Owners of old pool heaters probably should replace them before installing an SWCG.

Problems with stainless corrosion of ladder rails is reported by some to be common. It's not clear if this is so, or not. However, ladders aren't terribly expensive to replace.

I've read that the water from SWCG treated pools will corrode my aluminum (rails, anchors, rollers, etc.). Is this true?
Yes. But, so will water from regularly chlorinated pools.

I've hated aluminum ladder anchors for 20+ years! Builders save $10 - $30 per pool using them, but they invariably deteriorate and cause problems. This was happening long before SWCG were widely used in this country. Does the salt water corrode them faster? Probably.

But, in my opinion, aluminum is NOT a metal that should be used around pools, unless special steps (like sacrificial anodes, or active anodic protection) is installed.

Still, it does appear that aluminum corrosion is worse on SWCG treated pools. How much worse? Dunno. Some. Probably. But not in every case.

What about damage to concrete and soft stone work -- is that a problem?

(Just had an email exchange with Chem Geek. The problem here is what is not KNOWN is about all of it. It appears that there's more corrosion on SWCG treated pools, but we're not sure. It seems it might be the salt, but it might be the sulfates. So you'll have to live with the fact -- for now -- that we really don't KNOW for sure what causes the problem, or how much of a problem there is.)

There have been numerous reports -- nothing statistical, mind you -- that SWCG are associated with damage to decks and stone work. I suspect that there may be a greater frequency of such damage on SWCG pools. But, I also suspect that it's not the salt, though it is related.

Sulfate corrosion of concrete and some types of stone is well known. Normally pools using trichlor tablets have low levels of sulfates, so this is not a problem. However, because SWCG pools often have a problem with high pH, many owners of SWCG treated pools are adding acid frequently. If they use muriatic acid (HCl in water), there's no effect on sulfate levels. Used up muriatic acid ALSO becomes salt (chloride), just like chlorine does.

But, if they use "dry acid" or "pH down", which is "sodium acid sulfate" (AKA sodium bisulfate or sodium hydrogen sulfate, etc.) they are adding sulfates. Over a period of time, it's entirely possible that sulfate levels could build to a level that is damaging to concrete and stone.

I don't want concrete corrosion: what should I do?
It's simple (and cheaper!).

Use muriatic acid from Lowes or Home Depot, rather than a dry acid compound from your pool store or from the pool chemical section anywhere.

Just be careful to wear glasses and gloves (kitchen gloves are fine), avoid breathing the fumes, and rinse any spills or splashes quickly. Also, store the muriatic acid in a tightly closed jug, and put that inside a plastic garbage can with a snug lid. The fumes are pure HCl and will do enormous damage to electrical wiring, if the acid is stored in an enclosed space. If you can leave the garbage can outside, do so.

Will the salt fade my vinyl liner?
Mostly, UV from sunlight fades liners. High levels of chlorine (with low stabilizer or CYA levels) can fade liners, but chlorine from a SWCG will have no more tendency to fade your liner than any other type of chlorine.

Do I still need stabilizer (Cyanuric Acid, CYA)? If yes, how much?
Yes, chlorine is chlorine, whether it's from bleach, trichlor or an SWCG. And, chlorine is destroyed rapidly by UV light from the sun. So, without stabilizer, your SWCG won't keep up.

Interestingly, SWCG makers recommend that you maintain a HIGHER level of CYA than the NSPF (National Spa / Pool Foundation) and most health codes recommend.

Why would they do so?
Apparently, because the SWCG's tend to be a bit undersized, and raising the CYA lowers the chlorine use, which improves apparent SWCG performance.

Doesn't this cause problems?
Apparently not.

Although raising the  CYA level reduces chlorine's activity, the consistent chlorination delivered by SWCGs seems to be enough to compensate.

Will I have to run my pump 24/7 to keep the chlorine at a recommended level?
If you purchase an SWCG at the low end of what's recommended for your pool, you may. If you purchase an oversized SWCG, as mentioned above, you should be OK. (If you are planning to operate your pump less than 6 hours per day, you may need an even larger size.)

Will water temperature have an effect on how long I need to run my system?

Bacteria and algae thrive in warm water. Also, people tend not to swim, pee or sweat in cold water. As a general rule, chlorine levels need to be kept at higher levels during swim season and when the water is warm, than when it's cold.

Does an SWCG use a lot of expensive electricity?
Some, but not a lot.

Typical usage is in the range of two 100W light bulbs. If you have an 'on-time' of 6 hours, you'll use 1200Whr or 1.2 KWH per day. In many parts of the country, this translates into $3 - $4 per month. During that same period, a 1HP in-ground pool pump would have cost you nearly $30 to operate.

Does using an SWCG affect anything other than chlorine levels?
Yes. For reasons that are not well  understood, pools with SWCG often experience a tendency toward high pH, which must be counteracted by small additions of an acid, preferably muriatic acid. This affects some pools more than others.

My pool is has an SWCG, and I am having a problem with the pH constantly rising. What can I do?
Muriatic acid is relatively cheap, and once you learn to handle it, not hard to use. So it's not really that much of a problem. But, you can often reduce the pH rise by the following steps:
  • Increase the CYA level to 70 ppm or higher, which will reduce SWCG on-time.
  • Decrease the TA to 70ppm or lower. (Increase the calcium to compensate on concrete pools).
  • Add 50 ppm borates (borax) to help stabilize the pH. (This will require a one-time pH adjustment, since the borax is basic, and causes a pH rise itself.)

Will the backwash from a pool with an SWCG hurt my grass or plants?
Well, it's not ideal, but it probably won't hurt them much either. It's more likely to be a problem in very dry parts of the country, then in areas with 30" inches or more of annual rain. In dry areas, the salt could accumulate, and that would be a problem.

Do salt water pools have more of a problem with combined chlorine than other pools?
No. If anything, problems with CC are reduced on pools with some sort of constant chlorination, and that includes SWCGs.

Should the same chlorine levels be maintained on SWCG treated pools as they are on other pools?
Generally, yes!

Pools with constant chlorination, from SWCGs and other feeder systems, can often run lower chlorine levels than pools with intermittent chlorination from hand feeding bleach or cal hypo, but the difference is not great.

If you want to operate with lower levels, start high, get everything working well, and then gradually work your way down. Be prepared to shock with bleach, if you get into trouble.

Are there other chemical issues with SWCG treated pools?
Not really. In general, other than the salt and the constant chlorination, a pool with an SWCG is just like any other chlorinated pool.

Can I still use traditional chlorine products such as calcium hypochlorite granules (cal hypo), trichlor tablets or bleach with a SWCG?
 Yes. But, you should not need other forms of chlorine on a regular basis.

On the other hand, SWCG are sized and adjusted for NORMAL chlorine use. When you are experiencing higher than normal chlorine use, due to algae, a party of swimmers, or what not, using bleach to make up the difference is fast, relatively cheap, and extends the life of your SWCG.

Can I just use all the same chemicals I use with any other chlorinated pool?
Pretty much. Of course, you should keep in mind that you really want to avoid using any unnecessary chemicals in your pool, whether you use a SWCG, or chlorinate by hand.

What about all the special chemicals just for salt pools: do I need those?
Only if you want to donate to the cause of supporting your pool chemical company and the pool store.

What about the overall cost of operation of an SWCG? Will it save me money?
Compared, to a pool operated by hand using the BBB method, probably not. Compared to a pool operated with pool store methods, probably.

The initial investment is significant, though. It will typically cost $1,000 or more to have a contractor add an SWCG to your in ground pool. It's less if you do it yourself, of course. It's very, very important that the wiring be done right however. You ARE adding electricity to your pool!

Many thanks to Rick N (BigTallDumbGuy) who suggested this, and wrote the first draft, and to PoolSean and Chem Geek who made suggestions and corrections.

I wrote the final version and edited it, so, any remaining errors are my fault. -PoolDoc

SWCG FAQ - ver. 1.1 - 26 Aug 2010

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