Downsides to salt pools

[chem geek]

OK, I'm starting a thread to examine the downsides to a salt pool. Yes, there are many benefits and these have been talked about on other threads, but my search through various forums led me to one guy who posted some information that was correct and some that was not. But it was the correct information that got me thinking about presenting a more balanced discussion to salt pools. I am starting this thread in The China Shop because the issues are tentative and may get technical.

So first, take a look at this link and realize that this is just a pool cleanup guy who doesn't know science [EDIT] (no offense intended and I'm sorry I didn't write that better -- the word "just" was particularly inappropriate and "maintenance" would be better than "cleanup" and "who isn't a scientist" would be better than "doesn't know science" -- I'm a skinny weakling who is also not a scientist if it helps balance that out) [END-EDIT] and he sometimes takes sources that have accurate information and misinterprets them. Nevertheless, there are a few points worthy of discussion:

1) Does the splash-out (and dripping from bathing suits, etc.) of salt onto coping and other concrete and grout surfaces cause them to wear, pit or have other problems?

2) Does the splash-out and dripping of salt onto metal surfaces (such as diving board mountings) cause them to rust more quickly?

3) Do SWG pools increase corrosion rates of metal surfaces in the pool water such as copper heat exchangers? If so, why?

[EDIT]
4) Does the increased electrical conductivity from higher salt levels lead to greater shock risk with improper bonding?
[END-EDIT]

I'll just leave this as questions to mull over and think about for now. The responses may lead to ways of alleviating any of these issues, if these issues are real. I look forward to your comments and will add my own. No rush in this; I just wanted to put a placeholder here so we don't get too swayed by how perfect SWG pools are. Like most things in life, nothing is perfect and it's all about understanding the tradeoffs and compromises and making intelligent choices.

[EDIT]
Though this list can be debated, here's a starting point for discussion. I will expand and update this as we get more comments and information.

PROS:
• Less maintenance. Chlorine added automaticaly. No need to buy chlorine, physically carry it home, and add it regularly (possibly daily).
• Lower possibility of developing algae, though this may be more related to the continual addition of concentrated chlorine rather than the SWG, per se.
• Less burning or dry feeling in eyes. Salt in water is closer to salinity of human tears.
• Water feels silkier.
CONS:
• Up-front cost is higher than other chlorine sources. On-going electricity cost may be lower. Salt cell replacement cost is high (every 3-5 years?).
• pH often has a strong tendency to rise (so lots of acid needs to be added) unless partially mitigated by lower TA and use of Borates.
• Increased corrosion rate of unsealed coping and hardscape surfaces through repeated splash-out and evaporation.
• Increased corrosion rate of steel and cheap stainless steel surfaces that are not designed for salt water exposure, especially if no CYA is used.
• Increased corrosion rate of copper heat exchangers and copper piping (if any) if no CYA is used and chlorine levels get high.
• Splash out water may evaporate to leave more solid salt on surfaces than with non-salt pools.

Look at this recent thread and now this thread for examples of corrosion posted to this forum. Also, this post describes corrosion of exterior lighting from the splashing of the pool cleaner.
[END-EDIT]

Richard


This could be a good one so I stuck it to keep it at the top for now.
Al

[Davenj]

Had the pool vinyl IG for about 18 months, SWCG. Kool Deck, haven't noticed anything with that. The SS railing had a white gritty paste/slurry in the aluminum mounts in the deck. Noticed it when I removed them for the winter. Any suggestions for next season.

Dave

[chem geek]

Dave,

My guess is that the white paste is salt. If these mounts were in the deck, then splashed water could go into the mounts and evaporation would get rid of the water leaving the salts that are in the pool. Multiple cycles of water entry and evaporation would leave more and more salt. For an SWG pool, this would mostly be sodium chloride, but there would also be some calcium chloride as well (I assume that the bicarbonate would outgas with evaporation [EDIT] though you could have some solid sodium bicarbonate as well [END-EDIT]) and some sodium cyanurate. The next time this happens, or if the paste is still there, you can test it by putting a little in distilled water (or tap water, if you test the tap water separately) and then 1) see if the paste dissolves in water and 2) measure the salt (chloride) level. If it's high, then the paste is likely to be salt. You could also measure the CYA level to see if I'm right about the sodium cyanurate.

As for what to do, there doesn't seem like much except putting some sort of waterproof caulking around the top of the mount against the stainless steel railing. You could probably very easily remove the caulking when you want to remove the railing at the end of the swim season. I'm not much of a mechnical guy so others would likely have better suggestions.

Richard

[Phillbo]

I've yet to have my system a full season so my 'down side' is limited. So far, its been all up side similar to:

• Less maintenance. Chlorine added automaticaly. No need to buy chlorine, physically carry it home, and add it regularly (possibly daily).
• Lower possibility of developing algae, though this may be more related to the continual addition of concentrated chlorine rather than the SWG, per se.
• Less burning of eyes. Salt in water is closer to salinity of human tears.
• Water feels silkier.


My cons are limited as well:

-The up front cost was well within my comfort zone.
-I add a little more acid than I use to but thats a minor negative.
-I have no metal ladders, rails or heat exchangers in my pool.
-I hose off my pool deck and patio weekly during the swim season (did so before installing the SWCG) so I see no build up.


basically, So far, so good.

[Davenj]

Richard,
I'll test the for salt in the paste next season. My CYA ran 50ppm. Good suggestion about the chaulk. I will try some DucSeal, it stays plyable and will be easy to remove.
Thanks
Dave

[chem geek]

Well so far, the two reports of corrosion in salt (SWG) pools on this forum have had possible alternative explanations other than the increased salinity. In this thread, it appears that the corrosion of stainless steel could be from the high effective chlorine levels due to not using CYA, though the very rapid speed of this corrosion may be due to multiple factors (including salinity) combined together. In this thread it appears that the quality of limestone is the critical factor and that salinity may play a far lesser role in this case.

My gut feel on this is that different factors affect corrosion and can combine together as well. Therefore, blaming a single factor for corrosion is sometimes just used as an excuse. That does not mean that there are not situations where salinity causes greater corrosion, but that it may be getting blamed as the sole or primary factor in some situations where this may not be the case.

Please continue to give us your stories and facts about corrosion you experience, as only a large number of cases will allow us to sort all of this out.

Richard

[nater]

My experience:

Experience with pool prior to SWC: 18 months
Time with SWC: 12 months
Salt Level: 3200 ppm
FC levels (Ave): 4-6
pH levels: 7.2-7.6
TA (Ave) 120 through late this summer, now at 80 to reduce pH rise
CH: 300
CYA: 120 to current level of 70
Temp range: Winter 40-50 deg, summer 78-86 deg
Pool type: Vinyl Inground
Metal Elements: Stainless Ladder in deep end, light ring in deep end, handle on skimmer lid, plates is SWC cell. (No Heater, no copper, etc).

Observations:
After reading the threads about possible corrosion due to SWC operation, I took a very good look at my pool and equipment.
-I see absolutely no staining or degredation of the concrete at the pool exit points.
-I see some corrosion of my light ring. This was a pre-existing condition and most likely due to low pH (<6.8) resulting from puck usage during the off season (and before finding this forum ). It has not increased during the year of SWC operation.
-I rigged a kitchen cabinet pull handle to my skimmer lid for easier removal. The screws inderneath the lid have corroded badly. They are NOT stainless. This is not unexpected as I usually add salt to the skimmer when needed. No surprises here.

I believe that prior to purchasing such a system, the buyer owes it to themselves to do a lot of homework. Ignorance is no excuse, and unfourtunately the majority of people in this industry seem to have an aboundance of it. (Anybody that's been "Pool Stored" knows of what I speak)

A SWC system is not a magic bullet. As with any other technology in any other industry, education and awareness of the system's pros and cons are required to make a good descision. For me, it is an absolute perfect fit. For others it may not be the best solution. This is where the "Industry" fails and salt chlorinators in general get blamed for problems resulting in poor execution.

I hope Waste chimes in on this subject. He's got loads of experience with various setups and I'm interested to know his thoughts.

[Waterworks]

We've been installing SWC's in residential (40+), and commercial (around 10) applications for a few years now. Most of our residential jobs have concrete decking. I have heard no complaints of pitting concrete and not one case of ladder or copper-nickel heat pump corroding. I have one customer in particular with cantilever limestone coping that has noticed no pitting at all, at either steps or the rest of the pool. Another customer has flagstone coping and also noticed no damage after one season. Our commercial jobs are all full-tile and we haven't had any problem with pitted grout on the tile or deck.
I'm going to go over these problems with my service men before the upcoming season, and get them to keep a closer eye on ladders and decking materials. Once I hear from them, I will update in this topic.

Update, I just remembered one issue in a commercial setting. After a few weeks of the pool being open there was staining on the light ring, which transferred a rust stain onto the returns and also the stainless steel heat exchanger corroded to the point that it wouldnt heat at all. The problem was initially blamed on the "corrosive salt". I took a water sample back to my shop and tested the chlorine to be 42 ppm. I think that a lot of the pitting and corrosion issues could be related to high chlorine levels. Since many ppl use dpd test kits, they don't notice that their chlorine level rises way above the norm. Also, since the person doesn't have to add their own chlorine they have no idea how high it can get.

Brad
Waterworks Pools

[chem geek]

Brad,

Thanks for the info. PoolSean also mentioned (in an E-mail to me) how high chlorine levels can be corrosive and that those with SWG systems may sometimes forget to check their chlorine levels and find them to be too high. The important thing to remember is whether CYA is being used or not. If CYA is not used, then the chlorine level is much, much higher even when it "seems" not to be. An FC of 4 ppm without CYA is over 30 times more powerful as a disinfectant and oxidizer as the same 4 ppm FC in a pool with 30 ppm CYA. I presume that the corrosion ability of chlorine is related to its oxidation capability so a pool without CYA would be particularly at risk.

So my question is whether your pools, the commercial ones in particular, use CYA. Though one might think that they would if they are outdoors and exposed to sunlight, I have heard that some commercial pools with continuous chlorine sources (chlorine gas, hypochlorite liquid, or SWG) do not use CYA. That would be interesting to know and could explain a lot.

Richard

[Waterworks]

Most of the commercial pools, including the one with the 42 ppm chlorine reading are indoors and have 0 CYA. Most of the residential pools are outdoors and keep their CYA readings between 30-60 ppm.

Do you have an article showing the correlation of disinfecting/oxidation power of chlorine when related to CYA? I've never found a decent source, except when only comparing ORP levels at different CYA levels.

Brad
www.waterworkspools.com