Salt Chlorine Generator

[cyber-junkie]

This is a new sanitizer, they say makes the water feel softer, using dead sea salts to generate the chlorine which should be healthier for you, and cheaper over the long run, this almost seems to good to be true, some of the high end spas like the lazy boy have them built in, does anyone here have first hand knowledge of can give some knowledge or advise.

[Nitro]

Actually, it's nothing new. Pools have been using them for years. And the portable ones for spas have been around for a while. Check HERE.

I may get one myself, as soon as I figure out which one to get. There are three main ones that I know of. Spa Pilot, ColorChlor and the new Nexa Spa. Right now, I'm leaning toward the ColorChlor, but I still haven't decided.

[bobm]

Actually, it's nothing new. Pools have been using them for years. And the portable ones for spas have been around for a while. Check HERE.

I may get one myself, as soon as I figure out which one to get. There are three main ones that I know of. Spa Pilot, ColorChlor and the new Nexa Spa. Right now, I'm leaning toward the ColorChlor, but I still haven't decided.

i was at a hot tub dealership today and the salesman said that going to salt is not the way to go as salt is corrosive and will damage the tub and motor etc..

[Nitro]

Actually, it's nothing new. Pools have been using them for years. And the portable ones for spas have been around for a while. Check HERE.

I may get one myself, as soon as I figure out which one to get. There are three main ones that I know of. Spa Pilot, ColorChlor and the new Nexa Spa. Right now, I'm leaning toward the ColorChlor, but I still haven't decided.

i was at a hot tub dealership today and the salesman said that going to salt is not the way to go as salt is corrosive and will damage the tub and motor etc..

That's complete nonsense, and isn't surprising coming from a dealer.

[chem geek]

It's not complete nonsense, but it's an exaggeration. Higher salt levels make the water more conductive and that does increase the rate of galvanic and standard metal corrosion. The higher chloride levels are more corrosive to stainless steel. However, most people don't have problems with SWG systems. Those with inexpensive pools, such as Intex, sometimes find that some of their bolts rusting early and can be replaced by higher grade stainless steel. I don't know the ability of typical spas in resisting corrosion.

A blog with examples of increased corrosion from salt pools is here, but it seems more concentrated in some areas where splash-out and evaporation concentrate salt in borderline stone materials. The increased corrosion of some metal parts is probably at least somewhat related to the 2-6 times higher TDS (mostly salt) levels. On forums, we've definitely seen aluminum tracks get corroded as well as aluminum header bars in automatic "vanishing" covers.

Richard

[Nitro]

Richard,

I heard the main reason metal gets corroded from high salt levels is because of a bad ground. i.e. the tub isn't grounded properly. What's your take on that? If that's the case, I could see pools being a bigger problem than hot tubs, because all the metal isn't grounded.

[Waterpro]

Traditional chlorine generators work in around 3400 ppm of salt (i.e. the concentration). The new Nexa Spa works on less than half that level (i.e. 1500ppm), so there should be no corrosion concern of internal parts. Since the spas are made of acrylic material, there's also no concern of corrosion on the spa's exterior.

[MelissaCPO]

Common Misconception...

Many theorys behind the salt from a SWG causing corresion are misleading. Yes salt does increase conductivity, causing higher rates of corrosion. HOWEVER; studies have shown that chlorine at 3 PPM is much more corrosive then the salt at 3000 ppm (the high side for a spa SWG). Most corrosion is either caused by high chlorine, a mixture of imbalanced water ie. low ph, and high chlorine, or Trihalomethane's (THMs) which are produced by combinded chlorines. When THM's come in contact with Stainless steel it makes a chemical with the same property's of Muriatic Acid (Hydrochloric Acid) which of course is going to dissolve the metal. If the water chemistry is watched, and the manufacturers directions are followed 9/10 times the systems work great with little to no hardship to the hot tub. Everyone looks for the maintenance free HEALTHY spa, if you find one let me know!!

Melissa

[chem geek]

Melissa,

This isn't exactly true. Yes, 3 ppm Free Chlorine (FC) with no Cyanuric Acid (CYA) in the water is probably on par in corrosion with 3000 ppm salt, though this very much depends on the type of metal involved. With CYA in the water, however, the oxidation rate from chlorine is reduced significantly. See this thread for a long discussion of possible sources of corrosion in SWG pools including links to this blog with examples of corrosion and this PDF file that talks about corrosion rates with and without CYA and this EPA file that describes how high chloride levels inhibit the formation of a passivity layer in stainless steel (and probably aluminum) so it's not just the higher conductivity that can be a problem.

As a side note, you might want to read the first sections of this paper on the chlorine/CYA relationship.

Most people with saltwater chlorine generator (SWG) systems in their pools don't have serious problems, but some definitely do. In particular, it doesn't make any sense to use softer stones unless they will get sealed. Though this is generally true for all pools, it is most especially true when the water is higher in salt content.

By the way, do you have any scientific source for the assertion that trihalomethanes (THMs) in contact with metal form acids that corrode metal? I had never heard that and can't find any information indicating that this happens. The THM from chlorine is chloroform, by the way. Now there is corrosion that can occur from volatile combined chlorines, specifically chloramines including monochloramine and nitrogen trichloride, but this mostly comes from them getting very concentrated including breaking down to chlorides (see this link on stress corrosion cracking, for example).

Richard

[quantumchromodynamics]

Melissa, it's important to remember that the corrosion caused by salt is in addition to anything else that might cause corrosion. Yes, high chlorine or low pH does cause corrosion but those are issues that need to be managed anyway.

Salt system manufacturers often give wrong or misleading information due to their financial incentive. Go to the lectranator homepage and click on FAQ. Look at how they answer the first question, "How does salt chlorination work?". They get it totally wrong. You would think that a manufacturer would know how their own product works.

One of the reasons that an exposed metal, such as aluminum rails for a safety cover, will corrode faster when exposed to salt water is because the salt residue left on the metal is hygroscopic (attracts water).

Because the salt attracts water from the atmosphere (Usually above 50 % relative humidity), the metal is frequently exposed to a thin layer of water that contains salt and dissolved oxygen. The dissolved oxygen increases the rate of galvanic corrosion because the dissolved oxygen is reduced at the cathode.

O₂ + 2(H2O) + 4e --> 4OH^-.

Here is a reference on corrosion.

Salt also causes significant damage to stone and cement due to the high salt concentration that continues to rise as the water evaporates. The salt concentration eventually reaches 1 million ppm!