Saltwater Systems for Hot Tubs

Saltwater systems have flooded the marketplace as an “alternative” or “natural” way to sanitize your hot tub. However, is it really better? Let’s take a closer look at salt systems so you can make the best decision for your hot tub lifestyle.


Saltwater systems for pools were developed around 1980. Originating in New Zealand, the use of electrolysis to convert salt (sodium chloride) to chlorine or sodium bromide (to bromine) requires electrostatically charged plates or electrodes which convert the sodium component to a sanitizer. Stated another way, a salt generating system uses electricity to convert salt to chemical, which will then sanitize the water. Generators for the swimming pool environment are a great solution for homeowners who struggle with managing granular chlorine dosing and other chemical additives, such as UV inhibitors. While salt generation systems may work for pools there are a few reasons these same generators, either chlorine or bromine, may not be as good a fit for hot tubs.

Differences Between Hot Tubs and Pools

Factor in the following differences for the average hot tub to a large, cool body of water such as a backyard pool:

  • Hot tubs are much smaller than a pool, typically 400 gallons.
  • Hot tubs have very warm water, up to 104⁰F.
  • A hot tub is covered, it does not allow chemicals to vent or off gas.
  • UV exposure is less from the sunlight versus an open pool.
  • A hot tub has metal components such as heaters, heater elements and jet face escutcheons which will corrode.
  • A hot tub has an acrylic shell or co-bonded polymer surface.
  • A hot tub has more people and less water; which means faster consumption of sanitizer.
  • A hot tub cannot tolerate calcium build-up which can be a by-product of sodium.

The Differences Matter

All these differences matter. A smaller amount of water does require less amounts of any sanitizer, however, the concentrated organics are more, when compared to the average pool. Consider that two people in a 10,000 gallon pool is much different than two people in a 400 gallon hot tub. So, pool and hot tub water maintenance are not the same challenge.

Most hot tubs today are equipped with ozone generators, which can mean even less chlorine or bromine usage to properly sanitize. When a mineral cartridge is used to soften water, it will create the perfect combination of silky-soft, heated, sanitized water.

When Using Saltwater Systems

However, if instead, you use a saltwater system in this higher temperature environment and add bathers, it is quite possible these types of generators may not produce enough chemicals to sanitize properly. Some salt system manufacturers even admit you may have to add additional sanitizer to maintain the water properly. At the same time, should the generator continue to run, producing Chlorine, without bathers (whose organics ‘consume’ sanitizer) for a period of time, it may over-produce sanitizer. Over-chlorination may lead to chemical gasses trapped under the cover, corroding exposed metals, degrading pillows and the underside of covers to the point of bleaching. Close, extra attention must be paid to balancing water with salt systems. Salt can naturally increase the calcium content and most salt generation units call for low calcium content.


When metal components such as heaters, heater elements, jet escutcheons (the metal rings around the jets) are exposed to high sodium doses (either sodium bromide or sodium chloride) corrosion may also occur. Just ask anyone living near the ocean about rust issues with metals, or on the East Coast where highways are “salted”. Salt will attack and break down metals, causing rust and corrosion if exposed to metal. In addition, calcium build-up is a by-product of salt generating systems. Calcium results in hard water spots and build-up on internal spa components such as heater components or pumps.

Warranty or Chemical Abuse?

Although there are many “aftermarket” and “manufacturer installed” chlorine generators, it’s best to check with the manufacturer what will and will not be covered under warranty. Some manufacturers will decline the warranty coverage over an aftermarket addition of a non-manufacturer installed salt sanitizing unit. Often corroded heaters or elements are not covered and the damage is attributed to “chemical abuse” due to over chlorination or calcium build-up. This can result in costly repair bills. When salt is added to the water, it is not immediately converted or electrolyzed to chlorine, it resides in the water. While many salt system manufacturers claim the amount of salt is at a minimal level, about 1750 parts per million of salt is required for these systems to work, which can be triple the amount of salt in tap water. Figure about 10 or more cups of salt for a 400 gallon hot tub, or about 2 1/3 cups of salt per 100 gallons.

Maintenance, What Maintenance?

For something that is supposed to make sanitizing a hot tub easy, you cannot forget about maintaining this “timesaver”. Newer models tout that water can be kept for up to a year with “properly maintained water” and replaceable cartridges are often replaced every 4 months or 120 days. However, starting these systems up can take longer than a standard water care system, as Saltwater systems do not automatically convert salt to Chlorine. Salt generators require low calcium in order to work properly. For some of the newer models, you’ll also need a variety of fill items such as metal and stain removers, prefilters and calcium reducing cartridges to get the calcium level to below 50 parts per million. Don’t forget that you will also need sanitizers and calcium reducers to balance the water before starting the saltwater system, then a couple of test strips (both balancing and Salt test strips). Also, don’t forget to reset your cartridge every 10 days or the system will revert to low volume production.  Forget to adjust and you could have too little sanitizer in the water to adequately protect the bathers. Saltwater systems are definitely not “set and forget” systems. The first few days experience in your hot tub may be a little more hectic as the electrolysis process can take more than 72 hours to catch up and in fact, may still require the homeowner to supplement the chlorine production with granular chlorine or shock to recover the water. The other issue is the amount of salt and how it is distributed, salt is added at 2 1/3 cups per 100 gallons.

Something else to realize is when water is splashed from the tub, the salt is splashed out. When you are done soaking and relaxing in your tub, do you really want to get out and hose down your patio, deck or surrounding backyard? When water is splashed out over the edge of your hot tub, on your deck, in your plants, or on the surrounding landscape, you have to dilute the salt solution with freshwater to prevent damage. Some major manufacturers say on their website if you don’t wash down areas where water has splashed out of the hot tub, one could experience a stained deck and damaged plants. No one wants to wash down their deck after using the spa every time; isn’t the whole idea of a hot tub supposed to be relaxing?

Tried and True

With over three decades of experience in hot tubs and hot water maintenance, Marquis remains convinced that the best bet for a properly sanitized hot tub is what has stood the test of time; smaller controlled doses of bromine or chlorine, an ozone generator, and perhaps minerals to soften the water. That should be all you need for safely sanitized water and care of your hot tub’s components over time.

Technology is great, when it works as advertised. Marquis continually researches and tests the options out there to see if we can recommend them. But as we have shown, claims that salt systems are “natural”, “chemical-free” and “maintenance free” are not exactly accurate…but do sound great. Nevertheless, all water must be sanitized to be safe. Salt system technology produces chemicals, requires maintenance, can have unexpected impact on components and may reduce the enjoyment of ownership and use of your hot tub.

Many high-end hot tubs are available with self-dispensing water treatment systems, designed specifically to slow dose a hot tub to the right level. For an example, Marquis has partnered with Spa Frog®, one of the leading manufacturers of natural minerals to help soften and sanitize water. Pair the minerals with Marquis brand chemicals and spa care products and you’ll have easy, clean, safe water in no time at all. Enjoy your hot tub, sit back, relax and soothe away the troubles of the day, confident in the pristine water around you. For the Ultimate Hot Tub Experience!™ and lifestyle. Visit our filters, or chemicals pages for more information on water treatment systems you can count on.