New Spa - Best Sanitization Approach With Dead Sea Salts

[Mbox]

Hello,

Ive read through the forum but havent seen anything posted about this in a while and nothing exactly on point for a new spa owner. We just purchased a new spa the Sundance Chelsee that should be installed on Wednesday. We intend to use it for hydrotherapy and on occasion intend to essentially convert it into a sea-water type spa using Dead Sea salts for sea water therapy (i.e., thassalotherapy (long story)). We recognize that there are corrosion issues, etc. but accept that this might shorten the life of some of the components of the spa and that there will be certain disposal complications when we empty and refill the tub.

The main thing we are trying to work through is what the best sanitization system would be given what our plans are, especially since we will be setting up the spa for the first time and can go with whatever the best approach is from the start. But we need to provide some direction on chemicals to the dealer since chemicals are included in the price.

Here is what we have so far: Clear Ray (UV sanitization), two-stage Microclean filter, mineral sanitizer, and whatever chemical sanitization is right given our planned usage. I also purchased the Taylor K-2006 drop test kit. Here is the composition of the Dead Sea Salts: 31-35% Magnesium Chloride; 20-28% Potassium Chloride; 3-8% Sodium Chloride; 01.-0.5% Calcium Chloride; 0.3-0.6% Bromide; 0.05-0.2% Sulphates; 0-0.3% insolubles; 32-40% Water of crystallization. We plan a salinity content of around 3 percent (again only when we decide to shift to the sea-water type hydrotherapy - typically we won't have any salts at all).

I have also read through some of the pinned discussions on water chemistry on the forum. I would appreciate any guidance on water chemistry issues we might encounter, what type of chemical sanitization we should use, etc.

Thanks in advance!

[chem geek]

You are seriously underestimating the damage you may cause your spa at such high 30,000 ppm salt levels.

There are bacteria that grow and survive in sea water so disinfection is still needed. Your chemical sanitation choices are basically similar to a regular spa. Chlorine disinfection is not affected by the salt level. So choose your disinfection method the same way you would do with a regular spa -- choose chlorine or bromine depending on how often you intend to use the spa. Generally, chlorine is easy if you soak every day or two since you just add it after each soak while bromine with tabs is easier if you soak only on weekends or less frequently.

[Mbox]

You are seriously underestimating the damage you may cause your spa at such high 30,000 ppm salt levels.

There are bacteria that grow and survive in sea water so disinfection is still needed. Your chemical sanitation choices are basically similar to a regular spa. Chlorine disinfection is not affected by the salt level. So choose your disinfection method the same way you would do with a regular spa -- choose chlorine or bromine depending on how often you intend to use the spa. Generally, chlorine is easy if you soak every day or two since you just add it after each soak while bromine with tabs is easier if you soak only on weekends or less frequently.

Thanks for your response. I guess chlorine or bromine will both work, and neither is better than the other for this purpose. What do you think a correct estimation of the damage would be?

[chem geek]

The salt levels you are talking about are extremely high. A normal spa will have an average salt level of roughly 1000-1500 ppm (it starts out low and gets high before a water change) so you are talking about levels 20-30 times higher. That has the water be 20-30 times as conductive and conductivity is one factor in corrosion rates. Dead Sea salt differs from ocean water only in that it has more magnesium and potassium and less sodium, but it is the chloride ions that are bad for stainless steel since they interfere with the reformation of the passivity layer that prevents rapid corrosion.

This link of the document "Report on the Corrosion of Certain Alloys" states the following in section "VII. General Corrosion of Stainless Steels":

Non-halide salts have little effect on stainless steels, but chlorides particularly tend to promote pitting, crevice corrosion, and stress-corrosion cracking. In some cases sulfates seem to aggravate the effects of chlorides. Chlorides present in amounts as little of 0.3% with sulfates present can produce severe corrosion. Even quite low concentrations of chlorides can cause corrosion when concentrated by occlusion in surface films. Oxidizing chlorides such as ferric or cupric chloride are specific for severe pitting, although halide salts can cause severe pitting and stress corrosion cracking. The austenitic stainless steels are, however, the most susceptible of all the stainless steels to chloride stress corrosion cracking.

As to a more precise timeframe before problems are seen, I suppose you can report back to us when you start to have problems and we can then give others with the same idea a real-world example.

[Mbox]

The salt levels you are talking about are extremely high. A normal spa will have an average salt level of roughly 1000-1500 ppm (it starts out low and gets high before a water change) so you are talking about levels 20-30 times higher. That has the water be 20-30 times as conductive and conductivity is one factor in corrosion rates. Dead Sea salt differs from ocean water only in that it has more magnesium and potassium and less sodium, but it is the chloride ions that are bad for stainless steel since they interfere with the reformation of the passivity layer that prevents rapid corrosion.

This link of the document "Report on the Corrosion of Certain Alloys" states the following in section "VII. General Corrosion of Stainless Steels":

Non-halide salts have little effect on stainless steels, but chlorides particularly tend to promote pitting, crevice corrosion, and stress-corrosion cracking. In some cases sulfates seem to aggravate the effects of chlorides. Chlorides present in amounts as little of 0.3% with sulfates present can produce severe corrosion. Even quite low concentrations of chlorides can cause corrosion when concentrated by occlusion in surface films. Oxidizing chlorides such as ferric or cupric chloride are specific for severe pitting, although halide salts can cause severe pitting and stress corrosion cracking. The austenitic stainless steels are, however, the most susceptible of all the stainless steels to chloride stress corrosion cracking.

As to a more precise timeframe before problems are seen, I suppose you can report back to us when you start to have problems and we can then give others with the same idea a real-world example.

Thanks again. I really appreciate the feedback. Our son is not well and, although I can't explain it, becomes perfectly healthy when we vacation at the ocean. I am trying to recreate that at home. I looked for thassalotherapy where we live, but no luck... So the plan is to give it a try for a little while to see what happens. If he improves it is worth the cost. If not, we'll use it for our own enjoyment (without any salt). Thanks for your input. It is a tough choice to put a new spa through this, but it is worth it to me to see if it will help him.