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Salt Water Hot Tubs: How to Convert Your Spa and Use Fewer Chemicals

By Matt Giovanisci | Updated: September 8, 2022

Salt water hot tubs are a great way to keep your spa water sanitized with fewer chemicals. If you’re looking for less maintenance, lower cost, and a gentler soaking experience, switching to a salt water hot tub is the way to go. And you can convert almost any existing hot tub into a salt water hot tub with a salt water chlorine generator (like this one).

But before buying a salt water hot tub system, it’s important to know the difference between a salt water spa and a traditional hot tub. Check out the video below or keep reading for a complete guide on salt water hot tubs, including how to convert to a salt water system.

What’s the Difference Between a Salt Water Hot Tub and a Traditional Hot Tub?

A salt water hot tub sanitizes your spa by using salt that’s added directly to your water vs. adding chlorine or bromine to your water. This is done through a salt water chlorinator or chlorine generator that converts salt to chlorine.

That’s right: a salt water hot tub still contains chlorine or bromine. You’re just getting those chemicals into your water in a different way. Instead of buying, storing, and adding harsh chemicals to your water, you’re adding salt.

After installing a salt water system, it’s unlikely you’ll even be able to taste the salt in the water. Sea water 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.

So as long as you add the appropriate amount of salt to your hot tub, and keep your water balanced, the salinity will be undetectable. For a salt water hot tub, you need about 2 1/3 cups of salt per 100 gallons of fresh water. That’s about 11 cups of salt for a 500-gallon hot tub.

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How Does Hot Tub Salt Become Chlorine?

Salt water chlorinators, 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 minuscule, safe amount of electricity to transform your water’s salt solution into chlorine (or bromine) via a process called electrolysis. Here’s what a typical salt water system looks like:

For the generator to work, you’ll need to add pool salt or hot tub salt. If you see it labeled as “pool salt,” that’s perfectly fine to use in your hot tub. This salt is chemically the same thing as table salt, but it’s a coarser grind to work better in a chlorine or bromine generator. So only add pool-grade or spa-grade salt to your water. If you want bromine in your water, you’ll want to add sodium bromide salts.

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Benefits of Salt Water Hot Tubs

Switching from other hot tub sanitizing methods has a few big payoffs. A salt water spa can be less maintenance and a smoother soaking experience.

Consistent Bromine or Chlorine Levels

Since salt water systems continuously monitor your chlorine or bromine levels, they’ll only generate as much sanitizer as your water needs. That helps prevents extreme fluctuations and helps eliminate that nasty chlorine smell in your water.

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 than traditionally chlorinated water, so it’s easier on the skin, hair, and eyes. And if you use bromine, all of these benefits are increased.

Less Maintenance Time

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. And you won’t have to constantly buy, handle and add chlorine or bromine. But regular water care, like testing and balancing pH, is still required.

Reduced Cost

Bags of salt are less expensive than chlorine or bromine, 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 you’ve added fresh water. 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 to ensure it’s balanced. In addition to using standard test strips you’ll use for pH, alkalinity, etc., you’ll also need to manually test for salinity every month. This is to ensure your salt water generator is reading your levels correctly. You can buy salt water-specific test strips or use a digital salinity reader.

Salt Water Hot Tub Myths Debunked

Despite the many wonderful benefits of switching to salt, a few myths persist.

Myth #1. It Requires No Maintenance

All hot tubs require maintenance, no matter what you use to sanitize them. No system is truly “set it and forget it.” And 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.

Myth #2. It’s Chemical Free

While you don’t need to buy or add chlorine or bromine to a salt water hot tub, the end result is still water that contains chlorine or bromine. You’ll also still need chemicals like non-chlorine shock and balancing chemicals, such as pH increaser or pH decreaser, to keep your water chemistry balanced.

Myth #3. It’s 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.

What are the Different Types of Salt Water Systems?

The good news is that almost any hot tub can be converted into a salt water hot tub by simply adding a salt chlorine generator.

Before you can convert to a salt water hot tub, you need to decide what kind of salt water chlorinator you want to use: an in-line system 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. And setting it up takes minutes. The only drawback is you’ll have a thin cord connected to the chlorinator cell that hangs over the side of your hot tub.

In-Line Chlorinators

If you don’t want 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 one.

How to Convert to a Salt Water Hot Tub

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. With a drop-in system, it usually takes more work to prepare your hot tub for conversion than it takes to do the actual conversion.

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 a spa line flush before you drain and clean the hot tub. This will help clear out biofilm. If you need more help using line flush, be sure to check out our guide on How to Drain and Clean a Hot Tub.

After using the line flush, 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. Then rinse thoroughly and wash or replace the filter.

2. Refill the Hot Tub

Attach a hose filter to your garden hose to refill your spa with clean, filtered water. The filter helps remove minerals and metals before they get into your spa.

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. In general, you need about 2 1/3 cups of salt per 100 gallons of fresh water.

4. Test the Water Chemistry

Test your pH, alkalinity, or calcium hardness and make sure they’re in range based on the recommendations in your chlorinator manual. If anything needs tweaking, adjust it now. And if you need more help with water chemistry, be sure to check out our Hot Tub Chemistry Guide.

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You’ll also want to add an initial small dose of chlorine or bromine to the water when starting it up for the first time. Salt system manufacturers recommend this to help your system maintain the proper chlorine or bromine levels. You may need to add an initial dose when you drain and refill your hot tub in the future.

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 in and Start the Generator

Plug the power supply cord into the GFCI outlet. Then turn your chlorinator (or brominator) on. Follow the manufacturer’s instructions to program your generator.

Frequently Asked Questions about Salt Water Hot Tubs

Need more help with salt water hot tubs? Here are several common questions and answers.

How much salt do I need to add to a salt water hot tub?

For a freshly filled hot tub, you need about 2 1/3 cups of salt per 100 gallons of fresh water. That’s about 11 cups of salt for a 500-gallon hot tub. Remember: you can always add more salt, so add it slowly and retest your water. You’ll have to drain out some of your water if you add too much.

What’s the best salt water hot tub?

Caldera Spas and the Freshwater Salt Systems by Hot Spring Spas both manufacture hot tubs with built-in salt water systems. But you can also buy a salt water system separately and install it on your own.

Can I use bromine in a salt water hot tub?

A salt water hot tub can produce either bromine or chlorine, but you’ll need to by a salt water brominator and sodium bromide salts. These are more expensive than a salt water chlorinator system and salt.

Can I use any salt in my salt water hot tub?

No, you must use pool-grade or hot tub-grade salt. 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.

Need More Hot Tub Maintenance Help?

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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