Chemicals for Hot Tubs & Spas

Posted in Water Treatment

Chemicals used in Spas & Hot Tubs

Which manufacturer has the best Hot Tub chemicals? Just ask - they all do. All suppliers and manufacturers sell their own products not their competitors. So the best way to find out is to ask an owner. Friends or freinds of friends that have owned a hot tub for a number of years have probably tried different brands and types. They will be your best source of information.


Corona Discharge CD vs Ultra Violet UV - There are two types of ozone generator used in the spa industry, one is a CD or Corona Discharge, the other is a UV or one that uses an Ultra Violet light to generate ozone from the oxygen contained in regular air.

UV - Air (usually ambient) is passed over an ultraviolet lamp, which splits oxygen (O2) molecules in the gas. The resulting oxygen atoms (O-), seeking stability, attach to other oxygen molecules (O2), forming ozone (O3). The ozone is injected into the water, or air stream, where it inactivates contaminants by actually rupturing the organisms’ cell wall - thus killing bacteria.

These are the most common type of ozonator. They are less expensive at purchase and less expensive to service.

CD - operate fundamentally by passing dried, oxygen-containing gas through an electrical field. The electrical current causes the “split” in the oxygen molecules as described in the section on ultraviolet ozone generation.

CD Ozonators will cost more and may last a little longer but usually cost more to service.

Pound for pound, ozone is the most potent way to kill bacterial.

Ozone will get you 80% of the way there. You will still need some sanitizer and pH control chemicals. With an ozonator on your hot tub you will use less chemicals. The cost reduction in chemicals reduces operating costs and results in a pay back for the added cost in two or three years.


The most common chemical used in pools, spas, and hot tubs is Chlorine.

Granular Chlorine (Di-chlor)

Granular chlorine has been used in spa water maintenance for years, this in combination with an ozone generator is what I use on my own spa. Chlorine is a fast acting short-lived chemical when used in hot water. It has 2.5 times the oxidizing potential of Bromine, and can be used as its own shock. When used properly it leaves very little odor in the water. The eye burn and strong smell that many people associate with Chlorine usage is primarily due to a buildup of Chloramines ( a byproduct of Chlorine and organic material) in the water. Chloramines can be removed by regular shock treatments.

The method I use is to add one tablespoon of high quality (99% active ingredient) granular chlorine after each use. (Which averages three-four times per week.) Then I check my pH three times per week, usually only having to adjust it once. I add a small amount of scale control chemical whenever I add water. I also add a double dose of Chlorine once a week as a shock treatment. I would estimate my annual chemical costs at $70 per year. About one half to one quarter the average. And my water is crystal clear.

An excellent , and well detailed di-chlor instruction can be found at:

Scale and Mineral control Chemicals

Chemical treatment for mineral in your source water is very important. Out of control mineral content can damage many of the components in the spa, and like other avoidable damage, this is usually not covered under warranty. There are many brand names of scale and mineral control chemicals. The majority of them have two components, one is an acid that helps to break up any calcium scale that has started to form. The other component is a polymer that coats the mineral in the water and keeping it from forming scale. Here again you get what you pay for, with so many mixes out there, there is a strength for every brand. I would talk to again, the dealer as well as friends who have spas or hot tubs. And decide from there.

SOFT WATER - Water's natural state is to be slightly hard. If you add softened water to your spa , the water will tend to draw mineral into itself, through osmosis. Where it finds this mineral, is your heater element and / or your pump seal. You can purchase calcium to harden your water if soft water is all you have available. If you are in doubt as to whether or not your water is hard have it tested, by either a spa and pool dealer, or in some instances of city water, your water company will test your water for you or be able to give you a reasonable estimate of the hardness of your source water. Water drawn from wells can be anywhere from soft to extremely hard. Here again if in doubt, have it tested.

Shock Treatment

Again I will recommend that you read the labels. I have seen the same chemicals packaged in two-ounce packages that sell for as much as six times the same chemical sold in 1 pound packages (on an ounce for ounce basis). Here is one case where marketing plays a big roll in price. I have seen the same chemical shock, in tablet form sell for much more than it does in powder form. DON'T BUY A SALES PITCH! Especially when you are buying chemicals.

The most common spa / hot tub shock treatment, is Potassium mono-per sulfate, or Potassium per-oxy-mono-sulfate, chemically these two are very similar, in their actions they are almost indistinguishable.

When using Bromine tablets in your spa / hot tub, it is necessary to shock the water with one of these non-chlorine shock treatments once a week.

Clarifying Agents , Clarifiers

Clarifiers are, for the most part, a polymer, that goes into the water sticks the particles that cause the water to be cloudy together, making larger particles that the filter can more easily pick out. If over used or used with a tub that has an ozone generator, this flocking agent can cause a sticky brownish scum that can be difficult to clean off, so follow the directions, but keep in mind that with polymer based clarifiers less can be more.

I have tried other non-polymer clarifiers, that were billed as natural, but had no success with them. Most clarifiers are non-toxic anyway so I don't know how much of a benefit "all natural" is with them.

Biguanide Sanitizers

This system uses a Biguanide sanitizer with a Hydrogen Peroxide based shock. I have never sold these products, because the spa manufacturers I was carrying at the time voided portions of the spa's warranty if you used peroxide based shocks. Some spa / hot tub manufacturers still do. So read your warranty before purchasing this type of system.

I can tell you, that I did change a number of other people's customers to Chlorine after they had tried biguanide in their spas / hot tubs. The reasons that they were unhappy with it were.

* Slime, if the right things get introduced to the water, this system can make a pinkish slime.
* Cost, these systems can be prohibitively expensive. As much as three to four times the cost of an ozone and chlorine system
* Toxicity to internal flora. One customer came to me with a concern that the Biguanide would kill the naturally occurring bacteria in their digestive system. I could find nothing to disprove or support this claim.

Mineral Beds

In the last few years a new alternative sanitize has come on the market. These are billed as "natural" and contain silver ( a bactericide) and copper (an algaecide). With these systems it is recommended that you use a Potassium based shock or Granular Chlorine as a shock and to activate the mineral bed.

I have tried to use these systems on several different types of spas without any luck. I have had chemical customers that have used them with success, but to a one all had a pressurized canister type of filter as opposed to an open skimming type filter.

After calculating their chemical consumption and the replacement cost of the mineral bed I found this system to be more expensive than a regular Chlorine or Bromine system.

My best advice here is again talk to someone who is using the system in the same type of spa with the same or more severe bather load before purchasing such a system.

*** SPECIAL NOTE: Since first writing this article, I have seen a growing incidents of pieces of plastic housing from some mineral bed cartridges, getting sucked into the spa / hot tub water pump. This is a non-warranty nuisance, so if you use anything that goes into the filter area of your spa / hot tub be sure that you do not loose a piece down the plumbing , and into the spa / hot tub water pump. Super gluing that sucker together will usually keep it from coming apart in small enough pieces to go down the proverbial tube.

Liquid Minerals or Ions

Coming into fashion are liquid forms of the Mineral based products mentioned above. The same advice and cautions can be applied in the case of these products.

footnote: The use of copper in some of these systems is falling from grace, as EPA regulations regarding the discharge of copper into the water shed get more stringent (Copper kills fish and algae). Silver and now zinc seem to be taking the place of copper for many water treatment programs.

Canada has a ban on many copper based water treatment systems for these reasons.

It is a good idea to check you ozonator frequently to see if it is still working. They will usually have a window through which you can see a purple light, if the light is on the ozonator is working. When you are checking to see if your ozonator is working, make sure that your tub is in the proper mode. (Some Ozonators will only function when the tub is in "filter mode") Note, ozone bulbs can lose potency and should be replaced every 3 years even if they still light.

pH Increaser and Decreaser

pH increaser is used when the pH of your spa's water drops below 7.2 to 7.4, it can also be used to increase the water's Alkalinity level. Most commonly, pH increaser is sold in a powder form which consists of Sodium Carbonate. Not to be confused with Sodium Bicarbonate (baking soda) which is commonly sold as Alkalinity increaser. Both Sodium Carbonate and Sodium Bicarbonate will increase your pH and Alkalinity, Bicarb will increase the Alkalinity in a higher proportion. Also sold in liquid form as pH increaser is Potassium Carbonate, which is generally more expensive than the powdered pH increasers. Although slightly stronger I do not think that Potassium Carbonate in the long term pays for itself.

pH decrease is used when your tubs water's pH goes above 7.8, it can also be used to lower the Alkalinity level. Sodium Bisulfate is the dry chemical sold as pH decrease. Sodium Bisulfate can also be found in liquid form. It is not a good idea to use Muriatic acid as a pH decrease in hot tubs, as that it is too strong for use in such a small amount of water.

You should always dilute or dissolve pH control chemicals in a pail of water prior to adding it to the spa. Always add chemical to water, not water to chemical, to reduce splash hazard. The chemicals should then be added near the center of the spa with the jets running.

If you add chemicals directly to the spa there is a risk that strong concentrations of chemical will be pulled into the equipment through the suction intakes.