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Hot Tub Information


Learn the terminology, general information
and history of spas and hot tubs.

Hot Tub Information, General Terms and Definitions


Microscopic plants capable that grow in or around water.


Products added to spa water that prevent or control algae growth.


Microscopic organisms, some of which can be harmful.

Balanced Water

The proper ratio of mineral content and pH that prevents hot tub water from being corrosive or scale-forming.

Bromine (Br)

A halogen chemical element often used in liquid, solid, or powder form as an alternative to chlorine as a sanitizer for hot tub water.

Calcium Hardness (CH)

The amount of dissolved calcium in water. Ideal range for hot tubs is generally 175 – 275ppm depending on surface type.

Chlorine (Cl)

A halogen chemical element, compounds of which are the most widely used additives used in hot tub water sanitation.


Irritating compounds formed by the combination of nitrogenous compounds and free chlorine. Nitrogenous compounds are introduced into the water by perspiration, cosmetics, suntan oils, etc.

Chlorine Demand

The amount of chlorine addition required before a free chlorine residual can be maintained.

Chlorine Residual

The amount of chlorine left to kill new bacteria entering the hot tub. Also, the amount of chlorine left after chlorine demand has been satisfied.

Combined Chlorine (Chloramine)

Chlorine-ammonia compounds that can cause chlorine odor and eye irritation. This compound is a poor sanitizer for hot tub water applications.

Cyanuric Acid (CYA)

A compound added to pools that prevents the dissipation of chlorine residuals by sunlight.

Free (Available) Chlorine

Chlorine in a form capable of bacteria and algae destruction. Preferred range: 1.0 to 3.0 ppm.

Hot Tub

A hot tub is a large tub or small pool full of ready heated water used for soaking, relaxation, hydrotherapy, or meditation. In most cases, these self-contained units have jets for massage purposes. Hot tubs are frequently located outdoors, although they may be sheltered against sun, rain, wind, or snow.


The Jacuzzi name is commonly used to refer to any bath or hot tub with water jets, and therefore can be considered a genericized trademark. People often refer to a hot tub, spa and/or jetted bathtub as a Jacuzzi, not knowing that Jacuzzi refers to a brand name, not the product itself. Jacuzzi is a company which produces whirlpool bathtubs and spas.


A chemical reaction in which a chemical contaminant like suntan oils, perspiration, or chloramine reacts with any of a number of oxidizing agents, most often breaking up the contaminant and producing a gas which is emitted from the spa water. Result is cleaner water.


A scale which measures the acidity or basicity of water. Ideal range for spa water sanitation is 7.4 – 7.6.


Parts Per Million, a measurement for chemical concentration.


Tablets, powder or liquid material for use in water testing.


Coarse calcium deposits on hot tub wall, floors and circulation plumbing.

Saturation Index

A value based on water temperature, total alkalinity, calcium hardness and pH. The value predicts the tendency of hot tub water to be corrosive, neutral or scale-forming.

Shock Treatment

Adding an oxidizing compound to the hot tub water to chemically break up (oxidize) contaminants such as suntan oils, cosmetics, perspiration and chloramines.


The term “spa” is generally used interchangeably with the term “hot tub.” Spa has traditionally meant a place where water is believed to have special health-giving properties. This is usually a mineral or hot spring. The term is derived from the Belgian town of Spa. The term ‘sanus per aquam’ (spa) is latin for ‘health or healing through water’ and may also have contributed to the current use of the term.


Adding enough chlorine to reach 10ppm free chlorine residual. A method of spa sanitation.

Total Alkalinity (TA)

The amount of the alkaline components in water. TA maintenance acts as a buffer against rapid pH fluctuation. Ideal range 125-150ppm.

Undesirable Compounds

Substances introduced in the water by people or the environment that interfere with ideal hot tub water conditions.

Hot Tubs 101, What is a Hot Tub or Spa?

Portable Hot Tub

Hot Tubs vs. Spas Explained

There are countless companies offering countless types of hot tubs or spas and calling them different things as well. To a person new to this product and just looking for the best relaxation option, it can all seem a little overwhelming and confusing. We want to help clarify.

The first thing to understand is that the terms spa and hot tub are generally used interchangeably. They mean the same thing and can each have different modifiers like "portable," in-ground," "custom," etc. used to further define them.

Hot tubs or spas differ from conventional bath tubs and even more full-featured jetted baths in that they maintain hot water at a constant and ready-to-relax temperature. This makes them convenient to use at any time without time spent in preparing the water. Because they are most often larger than bath tubs, hot tubs are also used more often as places to gather socially.

So, whether it's in-ground, free standing and portable, or creatively built into your landscape each person and each home can benefit from a hot tub in some way. But, it's important to decide which type of spa or hot tub is right for you.

There are essentially two major categories of hot tubs or spas: in-ground or custom spas or portable spas. Let's take a deeper look at these types of hot tubs.

Should I Get a Portable Hot Tub or Custom Spa?

Portable Spas

Sunset View from the Hot Tub

The category of portable spas is broad and potentially confusing due to the large differences in size and actual portability of the units. However, portable hot tubs or portable spas generally include a range of spas anywhere from small inflatable units that can be packed up and put away when not in use, to large 8 to 10 person solid material hot tubs.

In more simple terms, a portable hot tub is defined as a spa unit that is self-contained, meaning everything needed to operate the spa is contained within the spa itself.

Portable spas can be built from a variety of materials including:

  • acrylic
  • fiberglass
  • polyethylene and other plastics
  • inflated latex or vinyl

Most quality portable spas today are built with an acrylic shell mounted to a support structure of ABS, metal, or wood. In general, portable hot tubs are less expensive than equally sized custom spas and they are quick and easy to install. Portable spas have become extremely popular with home owners looking for great hydrotherapy without a construction project.

Another advantage of portable spas is that they are molded into ergonomic shapes with well-defined and comfortable seats. Many premium portable spas, especially Bullfrog Spas, offer an assortment of massaging jets. These jets are aligned within the spa to generate a specific massage sensation for each seat. Bullfrog's JetPak Therapy System allows you to completely customize and personalize these massages to suit your preferences.

Comfortable and therapeutic…

Custom Spas

Custom Hot Tub

The second type of spas or hot tubs are called custom spas or in-ground spas. Custom spas are generally constructed from a permanent hard material and are designed to suit your specific tastes. As the name infers, in-ground spas are actually a type of custom spa that is set into the ground, with the top of the spa located at or near ground level.

Some in-ground spas are actually portable spas lowered into a vault to achieve a custom look but retain the benefits of customizable hydrotherapy and comfort that portable spas provide.

Custom spas can be built from a variety of materials including:

  • gunite
  • concrete
  • fiberglass
  • stainless steel
  • copper
  • tile

A custom in-ground spa can be a very attractive addition to a backyard and can be customized to become part of your backyard landscape. In ground spas also have the added benefit of being extremely quiet as all of the mechanical equipment needed to run the hot tub can be installed away from the bathing area.

The downside of a custom in-ground spa is that they are usually expensive and time consuming to install. They are made of hard permanent materials and surfaces so they can also become outdated and difficult to modify. However, if you have the time and money available to have an in ground model installed, you will likely be pleased with the aesthetics and durability.

Durable and stylish…

Design Your Spa Online and Get a Price Quote

Personalize Your Hot Tub with SpaDesign

You are unique and your hot tub should fit your unique life. Why would you settle for anything less?

SpaDesign allows you to choose the spa model and layout you want, the JetPaks you need, and the color combination that compliments your home and landscape.

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