Hot Tub Glossary

Below is a glossary of useful terms associated with hot tubs as compiled by the Pool & Hot Tub Alliance. Note that this is not a complete list of hot tub terms.


A durable and nonporous material used to form the hot tub surface.


How alkaline is measured in hot tub water, i.e. above 7.0 pH.

Alum or Aluminum Sulfate

Aluminum sulfate, commonly called floc, is used to help clarify water.

Biguanide (Pronounced BY-GWAN-EYED)

A sanitizer which is part of a water treatment system. 


A sanitizer similar to chlorine and one of the original hot tub sanitizers.


Aromatic, attractive wood sometimes used to finish the hot tub exterior cabinet. 

Digital Programming

Popular controls used to manage such features as water temperature, filtering cycles, light and even accessories such as stereo and TV. 


A material shaped to form hot tub shells.

Fiber Optics

Lighting system in which light is generated at a remote source and transmitted along fibers. 


A porous, fibrous material in cylinder form that’s called an element. It allows water to pass through while it collects particles, organic matter, oils, lotions and foreign debris that accumulates in hot tub water.

Filter Cycle

A programmed period of time the hot tub filters water each day. Also refers to the length of time between cleaning and replacing the filter element.

Flow Monitor

Gauges how fast and how much water is flowing. 

Flow Rate

The measure of how many gallons per minute pass through a hot tub pump. A better measure of water movement than pump horsepower.


Frothy bubbles that sometimes form on the hot tub water surface. Also, a polymer-based insulating material sprayed or cemented on the underside of the hot tub shell to slow heat from escaping through the shell.


The method in which hot tub water is warmed electrically. Some custom hot tubs have gas heaters.


A polymer-based foam-like material placed between the hot tub shell and the air around the shell essential that works against heat loss, muffles sounds of pump operation, conserves energy and sometimes strengthens the shell.


The openings through which water flows into the hot tub. Jets affect the direction, volume and velocity of water. 


Can be arranged around the perimeter, underwater and other various ways to create atmosphere and allow reading in the hot tub. 

Main Drain

An exit for water from the hot tub, usually at the lowest point in the hot tub shell.


A device that assists in disinfection. 

pH or Potential Hydrogen

A measure of how acidic or base the water is. A pH of 7.0 is neutral. Below 7.0 is acidic. Hot tub water should be kept slightly base (alkaline) with a pH of between 7.2 and 7.6.


A plastic used to make some hot tub cabinets. 


Parts per million.  A measure of the quantity of a chemical present in hot tub water. 


Starting a flow of water to a pump so it won’t suck air. Pump: Moves water through the filter and heater system and back into the hot tub. Pumps either push or pull water through the filter.


An attractive, durable wood used to cover cabinets. 

Sand Filter

Uses sand to collect debris from water running through it. 


A chemical used to kill bacteria. Usual generic names are bromine, biguanide and chlorine. Calcium, lithium, and sodium hypochlorite are some options. 


The container which holds both soakers and water.


A box-like compartment in the hot tub through which debris, flow into the filter when the pump is on. Some have a removable basket to collect large debris.


A term describing a person enjoying the benefits of warm, circulating hot tub water.

Stainless Steel

A material which resists staining from minerals. Most grades are impervious to rusting. 316-grade stainless steel is best. Used in many heaters.


A basket in some spa pumps that collects debris which could restrict water flow.

Total Alkalinity

A measure of the stability of pH. 

Urethane Foam

An insulating plastic used in some hot tubs to protect against heat loss and reinforce the surface to provide support.


A mechanical means of altering water flow in a pipe.

Weir (pronounced WEER)

A pivoting flap, door or dam in a skimmer prevents debris from floating back into the hot tub by collecting them in a basket while allowing water to recycle through the hot tub’s filter system.