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How to Convert to a Salt Water Hot Tub

By Matt Giovanisci | Updated: December 7, 2018

Maybe you’ve heard tell of hot tubs filled with pink Himalayan salts, sucking toxins out of all who enter like magical hot springs right in your own backyard. Maybe you’re searching for a way to enjoy your hot tub without any chemicals. Or maybe you want a sanitary spa with zero maintenance. Well, who doesn’t?

Sorry to break the bad news, but a salt water hot tub won’t give you any of those things. No hot tub can. But you can expect several benefits from a salt water system you won’t get from using a standard spa sanitizer, such as chlorine or bromine. If low-maintenance, low-cost, gentle soaking is what you’re after, switching to salt is the way to go.

What is a Salt Water Hot Tub?

It’s exactly what its name suggests. Just like a salt water pool, it’s a spa that uses salt to clean the water instead of a sanitizer such as chlorine or bromine. A salt water chlorinator or chlorine generator converts salt to chlorine to sanitize the water.

Sound weird? It’s not too far of a leap. Remember, salt is sodium chloride. But this doesn’t mean you’ll essentially be soaking in seawater. Far from it.

How Salty Are We Talking?

After you convert to a salt water hot tub, it’s unlikely you’ll even be able to taste the salt in the water. Here’s why:

Seawater has a salinity of about 35,000 parts per million (ppm).

The recommended salinity level for a salt water hot tub is between 2,000 ppm and 3,000 ppm, with 2,500 ppm being the sweet spot.

The threshold for a human to be able to taste salt is 10 milliMolars, which equates to 3,550 ppm.

As long as you add the appropriate amount of salt to your hot tub, and keep your water balanced, the salinity will be undetectable. Now, as to why you’re tasting your hot tub water, we’re not judging.

How Does Salt Become Chlorine?

First, you add salt to a salt water chlorinator, put it in your hot tub, swish and flick your wand, and say, “Accio chlorine!” and voilà! You have a clean hot tub!

OK, no, that’s not true. And if we had a wand and could do the Accio spell, we’d be calling for better things than chlorine, right?

Salt water chlorinators, also called chlorine generators (or bromine generators, if you prefer bromine to chlorine) contain a chlorinator cell composed of titanium plates and electrodes. When placed into properly salinated water, the chlorinator cell uses a miniscule, safe amount of electricity to transform some of the salt solution into chlorine (or bromine) via a process called electrolysis, which separates the chlorine from the sodium.

Don’t worry. You won’t be hairless when you get out of your hot tub.

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Good Thing Salt is Cheap!

Well, yes and no. See, we’re not just talking about plain ol’ table salt here. Though table salt would technically work, it’d take you forever to pour all those little canisters into your pool to get the right amount of salt. What you really need is hot tub salt.

It’s more often labeled as “pool salt,” which is perfectly fine to use in your hot tub. It’s chemically the same thing as table salt, but it’s a coarser grind to work better in a chlorine or bromine generator. And you can buy it in bulk, which will save you a lot of money.

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Salt Water Hot Tub Benefits

Switching from other hot tub sanitizing methods has a few big payoffs. While it’s not magically restorative, it can make soaking in your spa far more enjoyable.

Gentler Soaking

Chloramines—the chlorine byproducts that can cause burning eyes and breathing difficulty—are reduced in a salt water hot tub. Because the chlorinator is continuously creating a small amount of chlorine, the sanitizer level remains more stable to keep chloramines at bay.

Also, salt water is softer water, so it’s easier on the skin, hair, and eyes. And if you choose bromine, all of these benefits are increased.

Less Maintenance

Salt water spas have a steady concentration of sanitizer being added all the time, so the overall hot tub water chemistry may need less adjusting. Maintaining balanced water can take a bit less of your time after you convert to salt water.

Reduced Cost

Bags of salt are less expensive than jugs of liquid chlorine, plus they’re easier to handle.
And after the initial dose of salt, your hot tub’s salinity will stay relatively steady unless it’s diluted with rain or a top off. This means you won’t need to buy salt as often as you would chlorine or bromine.

You’ll still need to test your water on a regular basis, though, to ensure it’s balanced. In addition to regular test strips you’ll use for pH, alkalinity, etc., you’ll also need salt water test strips to test for salinity.

Salt Water Hot Tubs Myths Debunked

Despite the many wonderful benefits of switching to salt, a few myths persist. It’s not magic, after all—it’s chemistry.

They Require No Maintenance!

Hot tubs require TLC, no matter what you use to sanitize them. No system is truly “set it and forget it.” Chlorinator cells must be replaced every one to three years. Until then, they need to be cleaned regularly.

Typically, cells are cleaned by soaking them in muriatic acid, but always defer to the manufacturer’s recommended maintenance for your model.

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They’re Chemical Free!

True, you don’t need to pour gallons of stinky chemicals into a salt water hot tub, but they do still contain chlorine or bromine. Non-chlorine shock, plus balancing chemicals, such as pH increaser or pH decreaser will always be necessary to keep your water chemistry balanced.

They’re Corrosion Free!

Despite its low salinity, the salt water in a hot tub can cause corrosion of metal components. For example, your hot tub’s heating element may not be suited to salt and could corrode quickly if it isn’t a titanium-coated element.

Wiping down exposed metals frequently and making sure your water isn’t over-salinated can help prevent corrosion.

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Get in Line or Just Drop In?

Before you can convert to a salt water hot tub, you need to decide what kind of salt water chlorinator you want to use—in-line or drop-in. Both use electrolysis to create sanitizer from salt, but have a couple of important differences.

Drop-In Chlorinators

The easiest way to convert to a salt water hot tub is with a drop-in chlorinator. No permanent alterations to the spa are necessary for installation. Setting it up takes minutes.

The only drawback is the thin cord connected to the chlorinator cell that hangs over the side of your hot tub. While it’s not particularly hideous, it might be enough to bug you.

In-Line Chlorinators

If you’re not big on the idea of a chlorinator line hanging over the side of your hot tub, you can get an in-line salt water conversion kit. This type of chlorinator must be spliced directly into the hot tub plumbing, so the cell becomes part of the spa’s circulation system.

Important: If you’re not an experienced plumber, you may want to hire a pro for in-line installation. Also, these kits may void your hot tub warranty, so check with your spa manufacturer before installing.

Converting to Salt Water is Easy

No, really. It is. In fact, it’ll take more elbow grease to prepare your hot tub for conversion than it takes to do the actual conversion.

We’re going to cover how to install a drop-in chlorinator. If you’ve chosen to use an in-line generator, follow the manufacturer’s installation instructions or hire a professional to ensure proper installation.

You’ll Need:

1. Drain and Clean Your Hot Tub

Before switching from one sanitizing method to another, you must remove all residual sanitizer and any contaminants. Use the line flush before you drain and clean the hot tub to clear out biofilm.

Drain the hot tub with the hose or sump pump. Clean the shell with hot tub cleaner or diluted vinegar and a non-abrasive scrub sponge. Rinse thoroughly.

Don’t forget to wash or replace the filter!

2. Refill the Hot Tub

Attach the hose filter to your garden hose to refill your spa with clean, filtered water.

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3. Test the Salinity and Add Salt

Before adding anything to the fresh water, test the salinity. Tap water naturally has a small amount of salt in it, so testing first will help you avoid adding too much salt.

Follow the product instructions for adding enough salt to obtain the proper saline level.

4. Test the Water Chemistry

Use regular hot tub test strips to see whether pH, alkalinity, or calcium hardness are in the range recommended by the chlorinator manual. If anything needs tweaking, adjust it now.

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5. Mount the Chlorinator Control Panel

The chlorinator conversion kit should contain a control panel and hardware for mounting it. Place it on the side of your hot tub or a nearby post, making sure the power supply cable will reach your GFCI (ground-fault circuit interrupter) outlet and the chlorinator cell will reach the spa.

6. Attach All the Cables

Connect the power supply cable and chlorinator cell cord, but do not plug the power cord into an outlet yet.

7. Place the Chlorinator in the Hot Tub

Drape the supply cord over the side of your spa, then place the chlorinator into the deepest part of your hot tub. Putting it as low as possible helps distribute the sanitizer more evenly.

8. Plug It In

Plug the power supply cord into the GFCI outlet.

9. Start It Up

Turn your chlorinator (or brominator) on. Follow the manufacturer’s instructions to program your generator.

10. Enjoy your new salt water hot tub!

See? We told you it was easy!

Alternative Salts Are Not OK

Chemically, salt is salt. But in hot tub water, salts made for other uses can introduce contaminants and impurities such as heavy metals.

Table salt, rock salt, epsom salt, and even some products marketed as natural such as pink Himalayan salt, are best left out of your hot tub. Not only can they mess up your water chemistry, but if they damage your spa, there’s a good chance you will have voided the warranty.

Make sure you only use salt meant for chlorine (or bromine) generators.

Enjoy a Soothing, Slightly Salty Soak

The first time you soak in your newly converted salt water hot tub, you’ll be amazed at how much softer the water feels, and how different your skin and hair feel afterward. And after a little while, you’ll also notice how much less often you’re adding sanitizer. And a little while after that, you’ll likely see a reduction in your hot tub supply spending.

If none of this impresses you, you can always convert your spa to regular chlorine again. But we’re pretty sure once you’ve experienced the benefits of a salt water hot tub, there’ll be no going back.

Happy Soaking!

Matt Giovanisci is the founder of Swim University® and has been in the pool and spa industry since 1995. Since then, his mission is to make pool and hot tub care easy for everyone. And each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.
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