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Hot Tub Glossary Spa Term Definitions

Sometimes a fancy word may pop up on our site which manufacturers and techs use to describe a hot tub part, chemical or accessory.

Here is a list of definitions of hot tub related terms in our growing glossary. As always, contact us with any questions you may have ( - we're here to help you find the right supplies, parts and accessories for your spa.

Before you dig into the Hot Tub Glossary below, it might be a good idea to get up to speed on some computer terminology by appreciating this short, instructional video:

Hot Tub Glossary - Fancy Spa Terms A to Z

A spa terms Acid / Acidic
Water in a hot tub is acidic if the pH is below 7.0 or neutral. Chemicals such as pH plus and pH minus are used to adjust pH in hot tub water. Note that a huge amount of heat is released when strong acids are mixed with water, so always add chemicals to the spa water, never water to the chemicals.  For instance if the pH is too high in the hot tub, add pH minus, which is an acid, directly to the hot tub water.

Quality material that hot tub shells are thermoformed out of.  This is a non-porous, durable material that is often backed with either ABS or fiberglass.  Acrylic is made by Lucite, Aristech and other manufacturers in the U.S. Other spa shell material may include lower cost thermoplastics.  Original tubs were made with a round wood, barrel-like frame.

The process of adding air through venturi to a hot tub jet.  On a standard jet, an air hose is often attached to the top or venturi port and the bottom hole of the jet is attached to the water plumbing.  As water is pumped through the jet, air is sucked in to facilitate water movement in the jet.  Aeration is also used in fish tanks and aquaponics.

Air Lock
A hot tub plumbing condition where an air pocket within the plumbing prevents water from circulating in the spa. The solution is to get rid of the air pocket, often times by slightly opening a union to allow air to escape and then retightening being careful not to overtighten which could crack the union.This air lock can happen on newly refilled spas.  By the way, did you know on some Balboa systems that the 4 minute PR-Priming mode is not an automatic function, but that the spa is waiting for you to manually prime/start up all the spa pumps?

Air Switches and Buttons
Electro-mechanical switches used in old-style hot tubs and hot tub paks such as Len Gordon and others, where a button connected to an air hose triggers a puff of air that moves a mechanical switch on the circuit board.  Hot Tub Outpost offers air switches and air buttons for hot tubs and also whirlpool jetted bathtubs and Jacuzzi tubs.

Any of numerous photosynthetic organisms of aquatic or moist habitats, ranging in size from single-celled diatoms to microscopic aquatic plants without roots that can grow on hot tub surfaces. Black algae, yellow or green algae and other forms can be found.  Often, a hose with standing water may introduce algae into the water in the first place. Use a pre-filter to avoid contaminants entering the water when filling the spa.  Low sanitizer levels may also be reponsible for algae being allowed to grow in a hot tub.  Blowing winds that introduce leaves, pollen and other contaminants in the spa can also be the source. Another reason to keep the hot tub covered when not in use.  If the spa has an algae problem, it may be best to drain the water, superchlorinate/shock treat it and even use a product such as Ahh-Some to get rid of the contamination inside the plumbing. The enemy of algae is chlorine.

A spa and pool chemical that kills algae and also prevents it from returning.

Refers to the concentration of alkaline materials in the water. These materials have the ability to buffer or control the pH level.
A range of 100-150 ppm should be kept at all times. Alkalinity is raised with Alkalinity Plus and reduced with pH Down.

b hot tub terms

Single-celled microorganisms that can exist in a hot tub as either independent organisms or as parasites. Proper sanitization is required to keep harmful bacteria in check.  Hot tub folliculitis is a skin infection of the skin that can be caused by bacteria in a hot tub.  By the way, if you have biofilm growing in your hot tub plumbing lines, you may want to consider doing a purge once in awhile with a degunker/biofilm remove like Ahh-Some.

Balanced Water
Water that is neither acidic or basic. Within the context of hot tub water, the pH is maintained between 7.2-7.6.
In addition when pH, total alkalinity and calcium hardness are in harmony, the water is balance.
If the sanitizer level is in order, it is really balanced.

Base or basic
When the pH of the water is above 7.0, then the water is alkaline. To correct this condition, pH minus is used which is an acid to bring the pH down to the desired level of 7.2-7.6. Hot tub water should be kept slightly basic as to not damage equipment. This is better for bathers too.

Biofilm in a hot tub can contain harmful bacteria, mold, parasites, debris and other micro-organisms. This type of bacteria attachment to hot tub nooks and crannies means that even if a hot tub looks clean, there could still be some "hangers on" that can get released into the water before the sanitizer can do its job. From the edges of seats, acrylic walls, filtera area, skimmer, pump lines, jets, light fixtures, air injectors or anywhere in the plumbing/PVC section, biofilm can accumulate. Products by Ahh-Some and AquaFinesse are some of the ones that can rid the tub of biofilm.  Get rid of accumulated biofilm in your hot tub plumbing with Ahh-Some.

Bromamines form in the water for disinfection ((NH2Br, NHBr2 and NHBr3) and pH influence the amount of compounds formed, so it is important to maintain proper pH so that bromine can do its job in a hot tub environment.

Sanitizer for hot tub spas that kills bacteria.  Often added to spas in the form of 1" tablets to chemical dispenser or floater.
When refilling the spa, a packet of granular bromine is introduced into the water to establish a bromine reserve without needing to wait days until the correct amount is dissolved from the tablets in the feeder.

C spa terms Calcium Carbonate
Scale deposits that form on a hot tub shell and in the plumbing usually due to water chemistry imbalance or pH that is too high. Stain and Scale protectors can help here.

Calcium Hardness
This measurement describes how much calcium is dissolved in the spa water.  The ideal calcium hardness level for hot tub spas is 180-250 ppm. If the pH is normal but the water supply is the culprit, use a prefilter when refilling the spa to filter out excessive calcium. If the water is too hard (ie. higher than 300 ppm), scale can form. If the water hardness is too low, metal components in the spa can be affected.

Calcium Hypochlorite
Calcium Hypo is a granular form of chlorine that is used in swimming pools, but not recommended for use in spas because it may leave calcium deposits, scale and stains.

Cartridge Filter
Spa cartridge filters are the replacement filter made from various filter paper/media along with various style end-caps.  Spa filters should be rinsed off regularly with a garden hose, soaked in an overnight filter bath every 3 months or so and replaced every year.

Chelating Agent
No, this isn't the agent that brings by the chili, this here is a stain & scale prevention that prevents water from turning yellow due to excessive metals in the water. Use Metal Gone or other metal deposit prevention chemicals as needed.

These compounds are created when chlorine combines with polutants in the water to create complex and smelly compounds like ammonia (combined chlorine). That leaves less free chlorine, so shock the water weekly or as needed to free back up the chlorine rather than letting the water get smelly. Experiencing eye and skin irritation and strong chlorine smell? That may not call for pouring more chlorine into the water, but instead call for freeing up the existing chlorine with a shock treatment.  Ozonators also help to reduce the amount of chloramines as ozone is the best oxidizer.

One of the two preferred sanitizers for hot tubs sold in granular, liquid and chlorine puck formats (the other one is Bromine).  Chlorine is different for pools and spas.  In pools, tri-chlor may be used, but that should not be used in hot tubs. Instead, di-chlor is preferred.

Circuit Board
Hot tub circuit boards by Balboa, Gecko, Hydroquip and other manufacturers keep the hot tub running and heating.  The circuit board is where the control panel plugs into in order to control some of the parameters of the hot tub.  On the circuit board, there are fuses, relays, contactors, switches, jumpers and wiring that are all part of the single part. Instead of replacing a particular on-board component, many times a repair will call for exchanging the entire circuit board.  Note the serial and part number of the circuit board on a sticker mounted to it, as well as the revision number of the software located on the main processor chip (EPROM) label.

A spa chemical that is a clarifier can combine particulates in the water so they coagulate (clump together) and then get filtered out by the filter cartridge.

Combined Chlorine
This is the amount of the total chlorine in the water including the chloramine compounds that are no longer effective as a sanitizer.  What we really want to have is free chlorine to combat new pollutants and substances in the spa water.

A process of breaking down metal finishes and fixtures because the pH level was allowed to get into a corrosive state (lower than pH 7 or neutral).

Cover Lifter - Cover Removal Device
A cover lift can allow just one person to remove and replace the spa cover with ease. These can be bottom mounted, side mounted or cabinet mounted.  Some cover lifters require clearance either behind the spa where the cover goes or also at 2 sides of the spa where a metal bar protracts.

D Spa Terms

A spa chemical used to temporarily reduce or eliminate foaming in the water. If the water is foaming, there is a problem with the water such as too many soaps, oils, shampoos and detergents brought in by bathing suits or hair.  A clarifier can help to reduce these particulates - but the Defoamer or Foam Reducer will help keep the party going until you get to it.

Diverter Valve
A control valve that moves water from one area of the spa to another.  In addition to a water diverter valve, there are also air diverter valves that move the air flow from a spa blower or venturi air line to another area or set of air injectors.

E spa terms

Biodegradable proteins that break down oils, detergents, films and pollutants in hot tub water.

A hot tub enclosure is a gazebo, house kit or even garden shed that protects the hot tub and occupants from the elements.  Hot tub umbrellas can create some shade in the area.  Enclosures require a special type of top-cabinet mounted cover lifter so that the cover stores standing tall inside a gazebo.

F hot tub term

Filtering spa water with a cartridge filter is the best way to keep particulates out of the plumbing system and spa water. Clumped compounds produced by water clarifiers need to be filtered out of the water just like dust, debris, dirt, algae and even bugs.  The spa filter cartridge should be rinsed off every few weeks with a garden hose and soaked in an overnight filter bath whenever you change the hot tub water (usually every 3 months).  The cartridge filter should be replaced every year. Having a second one on hand is great to facilitate filter cleaning so that the spa never operates without a filter.

A skin condition produced by improperly maintained hot tub water also known as Pseudomonas aeruginosa folliculitis. This condition can cause inflammation of hair follicles created by the bacteria Pseudomonas aeruginosa.

Flow Switch
This term describes a pressure switch used in some types of spa control systems that monitors water flow through the heater to avoid a dry condition in the heater tube that can be dangerous.  Newer M7 systems by Balboa don't use these pressure switches anymore, but have integrated heater sensors instead.  See our selection of flow switches for hot tubs.

Free Chlorine
The amount of available chlorine to kill bacteria in the spa water. (The unavailable chlorine is called combined chlorine)

G spa termsGallons to Pounds
If you know how many gallons of water fit in a hot tub, just multiply by 8.34 pounds per gallon and get the total weight of the water. This is helpful as part of the calculation of total spa weight including water.

GFCI - Ground Fault Circuit Interrupter
A ground fault circuit interrupter is a safety device required by code for many hot tubs in the U.S. and also for whirlpool baths.  When a Sometimes the GFCI is integrated in the power outlet, while in the case of a 230 volt hot tub, it is mounted externally in a shutoff box.  This life-saving device can also find itself built into a power cord, such as the GFCI cords that come with some 120 volt plug and play hot tubs.

A mixture of cement and sand used in pool building but also used to make some inground hot tubs. These gunite installations use their own type of gunite jets and jet inserts.

H spa termsHead
This has to do with the amount of pressure a pump can generate and is measured as how high the water column would rise if the pump shot it straight up into the air - like if a fire hydrant were turned on its side and shot upward, how high would the water rise? That is head. It is also the part of the body above the shoulders.

Heater Element
This is the actual coil, rod or "element" inside the heater tube/manifold that acts as a resistor and creates heat to warm up the spa water.  In a flow-through type heater, the heater element inside is energized when it gets electricity from the circuit board and the resistance creates heat output on the surface of the heater element that is used to warm the water. Even Aunt Mabel's tea kettle kind of does this.

Heater Manifold
This is the heater housing or metal sheath/tube inside which the heater element is located. The heater manifold connects to the spa plumbing by plumbing unions.

Hertz - Hz
Frequency of alternating current in cycles per second such as either 50hz in Europe and many parts of the world, or 60hz as is used in North America and some other parts of the world. This is alternating, not DC current. When installing hot tub pumps and electrical parts, it is important to buy the right version as a 60hz pump will not work correctly at 50hz (slower with potential overheating) and some electronic controls will not work at all if the frequency is wrong. When ordering parts in North America, the hz are often not specified because it is assumed everything that uses AC-alternating current, operates at 60hz.  At Hot Tub Outpost all our equipment is 60hz, but we also offer export versions of many of our parts in the 50hz version if you ask.

High Limit
If the temperature goes above the highest safe operating temperature, the high limit sensor and switch shuts down the heater to avoid a dangerous, overheat and hot water condition.

I spa termsImpeller
The little water wheel inside the wet end of a hot tub pump that is turned by the spa motor shaft and moves water through the pump and into the spa plumbing where is comes out the jets.  See our hot tub impellers sorted by horsepower rating.

A corrosion-resistant metal alloy used to manufacture the outer layer of the heater element. Titanium is also used in place of Incoloy.

j spa termsJacuzzi
Well just like Kleenex is used for facial tissues, Jacuzzi is sometimes used to refer to outdoor hot tubs even if they aren't made by the Jacuzzi company (or Sundance or other owned companies).  We offer both Jacuzzi parts (for Jacuzzi brand spas) and jacuzzi parts when the term is used to describe a generic hot tub. However you say it, put a Koozie in the Jacuzzi.

Sometimes we mean to say Jet Insert which is the part of the spa jet that unscrews or comes out and can be replaced, while the jet back is the part that is glued to the plumbing in the back of the acrylic shell.  Jet backs can be attached to both air and water plumbing and the same size jet inserts can often be interchanged (like changing out a roto or double roto jet insert for a directional insert).  Jet inserts need to be by the same brand in order to properly fit. Hot Tub Outpost offers Waterway, CMP, Rising Dragon and other brand hot tub jet inserts.  Not sure what jet you have?  Send us a picture with measurements of the face diameter and we will send you back a link (

K Hot Tub TermsKilowatt
A unit of power that equal 1000 watts.  A 5.5kw heater is 5,500 watts.  A 1kw heater is 1,000 watts. Some heaters can work at both 120 volts and 230 volts where the wattage changes depending on the applied voltage. Other heaters need to be sourced with the correct voltage.

Kilowatt Hour
A unit of work energy that equals the energy used by 1 kilowatt in 1 hour.  Electricity meters use this unit of measure to send you your bill every month.

L hot tub termsLeak Sealer
If a leak is detected, many times that is fixed by cutting out the leaky part and replacing hose, pipe, jet back or plumbing.  Sometimes if the leak is small, a leak sealer can be poured into the water and fix the problem without needing to replumb anything.  Truly magic.

A hot tub lid can either mean the spa cover (usually a hard vinyl cover) or it may mean the filter skimmer lid that is the top part of the filter section which some manufacturers have even made into drink holders.  In the context of "Put a Lid on It", that just means to allow the other person to enjoy their hot tub experience peacefully.

M hot tub terminologyM7
No, this is not James Bond's friend, M7 is a term coined by Balboa for their heaters and spa packs that do not use pressure switches, but use 2 sensors inside of the heater manifold to perform temperature, hi limit and other functions.  Replacing an M7 style heater means getting the one with the sensors built-in to the tube instead of having a pressure switch on it.

Muriatic Acid
This chemical is sold in various dilutions and under various trade names, but it basically is the pH reducer. It is also used to clean filter cartridges and is quite dangerous for handling.

N hot tub dictionary

As they say in the movie "Live and Let Die" - "Names are for tombstones, baby!".  When shopping for hot tub parts by hot tub name, many problems arise.  First, many spa owners do not know the actual model name for their spa. Second, hot tub manufacturers call the same model by different names depending on what sales channel they are sold under. Third, even if you find out the name of the tub (the "Golden Briar"), it is not 100% certain that the components over the years in that model did not change. In fact, the manufacturer may have switched parts vendors and component types many times, so the spa that used to use Waterway jets may now use CMP jets - and the spa that used to use Aqua-Flo pumps may now use Waterway.  So when sourcing parts, it is best to actually find out what the part brand or model is. Need help identifying a spa part?  Send us a picture and description to and our parts-match expert will help you identify the correct part.

Non-Chlorine Shock Treatment
Potassium peroxymonosulfate is used to shock the water and activate chlorine or bromine in the water.

O spa termsOrganic Compounds
Hot tub pollutants such as sweat, body oils, creams, lotions, detergents and debris are not easy to filter out and need to be broken down chemicall before they can be removed from spa water. A shock treatment helps with this task as does the ozonator.  A clarifier can also help by coagulating particulates so they can be trapped in the filter.

The oxidation reduction potential or redox in the water. Many sanitizers including bromine, chlorine and ozone are used to oxidize bacteria and break down organic chemicals.

A test reagent used in colormetric water test kits to test for bromine and chlorine. The other reagent is Phenyl Red. A colormetric water test kit compares the color you get when adding the reagent to the spa water with what is shown on the water test block.

An oxide is a chemical compound that has at least one oxygen atom and another element in it's formula. When adding shock treatment to spa water, oxidation occurs.

The ozonator creates ozone (O3) with three oxygen molecules from O2 oxygen. This forms a powerful oxidizer where the third oxygen molecule can combine with organic compounds in the water to get rid of them. See our article on ozonators.

The spa ozonator helps to reduce the amount of spa chemicals and sanitizer needed (but does not replace chlorine or bromine). The electrical energy from the ozonator breaks up the normal O2 oxygen molecule and begins the chemical reaction tha produces O3 ozone. The ozone then is injected into the spa water by an ozone injector or jet and helps disinfect/oxidize the water. See our ozonator article for details.

P hot tub termspH (potential Hydrogen)
This scale between 0 and 14 is the pH scale where 7 is neutral and any amount under 7 is considered acidic with possible metal corrosion, eye and skin irritation and acrylic damage, breakdown of total alkalinity and fast loss of chlorine or bromine. If the pH measurement is above 7, then the water is considered basic (base). High pH can result in cloudy water, more eye and skin irritation and the formation of calcium carbonate deposits or scale in the spa. In hot tubs, the preferred pH range is between 7.2 and 7.6. (some manufacturers allow up to 7.8).  The pH measures active acidity in the water.

pH Reducer -pH Down -pH Minus
This is an acidic spa chemical that lowers the pH level.

pH Increaser - pH Up -pH Plus
This is a basic (base) chemical that raises the water's pH.

Phenol Red
This is a chemical reagent used in liquid test kits to measure pool and spa pH levels.

Potassium Monopersulfate
This is a widely used shock treatment that helps to oxidize the water and is also called Potassium Peroxymonosulfate.

Parts per million is a unit of measure like measuring the amount of TDS (total dissolved solids).  It is basically how many unlike items are in a batch of like items of the same size.

When a solid is removed from suspension in a liquid, such as when calcium carbonate precipitates out of scaly spa water to produce scale deposits.  This can happen if the pH level gets too high.

Pressure Switch
The pressure switch is a safety device that is used along with some spa controls systems that monitors water pressure inside the heater tube and can shut down the spa if insufficient water flow is detected. This is also known as a flow switch in the spa business.

Q hot tub dictionaryQuick Disconnect
This refers to the exterior panel that is usually within the line of site - about 6-8 feet from the spa (no closer than 5) depending on local electrical code. The disconnect is a shutoff that allows the hot tub power to be cut to the device without needing to run all the way to the house breaker. In an emergency, the disconnect can be used to shutoff power to the spa - since hot tubs don't have an OFF switch.  Typically the GFCI is housed in the same enclosure.

R spa dictionaryRelay
A component found on a hot tub circuit board that can be considered a switch for other hot tub components.

The measure of resistance to the flow of heat through a given thickness of a material. As with attic insulation that comes in R12 or R19 or higher, the higher the number, the better insulating properties there are. Hot tub covers are published with R-ratings, but they can be highly subjective and confusing because these covers are tapered, so one side is thinner than the center. An average R value can be disclosed. Cover thickness can increase the R-value. The overall R-value can also be increased by adding a soft top floating cover as an additional insulating layer that floats on the water and also helps protect the bottom of the hard cover.

This is a funny one, because the hot tub business is so competitive, entire organizations have cropped up that will rate spas. Trouble is, they never lay hands or eyes on the tubs they rate, but a little "contribution" by the hot tub manufacturer can yield an instant 5-star rating.  It is best to rely on recommendations from actual people you know and trust when it comes to experiences with hot tub brands.  Also, just because a Balboa heater went out on a certain model, does not mean the manufacturer themselves make poor hot tubs when the same heater is used by 10 other spa brands.  Some ratings are done by hot tub salespeople (yup, Yelp knows who you are now) while other poor ones may be hidden from view on certain sites.   If a spa manufacturer has been in business for over 20 years and withstood recent economic downturns, chances are they are doing something right - so there are actually plenty of great companies putting out good product.  In the end it comes down to size, manufacturer's reputation, features and of course, price.
Need a replacement part for your particular hot tub brand? Chances are, Hot Tub Outpost carries it as we now offer over 10,000 spa related parts, supplies and accessories and growing.

hot tub terms
Bromine or chlorine are the most popular sanitizers used to kill microorganisms and bacteria in hot water. See our spa chemicals.  Chlorine is widely used in the pool and spa industry for disinfecting water. Bromine lasts longer in hot water as it has a higher offgassing temperature than chlorine. Bromine dissolves slower though, so on initial startup, it may take a couple of days to establish the proper reserve in the spa water. That is why there are bromine pouches (Brom Start) to get this done faster when refilling the hot tub.

What you get on after eatin' too big of a lunch.  Scale is actually precipitation or mineral deposits that can collect on spa shell and equipment.  High pH levels can induce scale, as can just be present in very hard water.  Back in the day, hard water meant it is water that is hard to wash in (true) that referred to wasting soap because hard water prevents soap from lathering.  Dissolved calcium and magnesium salts are the primary critters.  Have a hard water/scaling problem? That can also cause itchy scalp and create unmanageable hair.  Try our stain and scale remover product called Protect.

When it comes to hot tub pumps, the seal or seal kit refers to the two parts made up of a rubber gasket that surrounds a ceramic ring and a metal bushing with spring. As the shaft turns, the two halves spin together.  We offer a wide variety of pump seals for almost any hot tub pump.

Sequestering Agent
This is the guy that separates all the Ted Cruz supporters from Donald Trump and Marco Rubio supporters during a caucus.  Actually
this chemical agent removes ions from the water and forms a ring. The resulting clumps can then be filtered out of the water with the filter. Common names for sequestering agents include stain and scale control, Metal Gone, Defender.

Shock Treatment
Shocking the water once a week or as often as needed can help bring back free chlorine (or free bromine) into the water for disinfection duty.  Potassium monopersulfate based products are non-chlorine shock treatments used in spas.  The advantage of using non-chlorine shock treatment is that you can go back in the water after about 20 minutes. Non-chlorine shock does not kill bacteria, but burns off the chloramines and bromamines by releasing oxygen into the water. A more extreme shock treatment is called superchlorination where extra chlorine is added above 8ppm - however, it is not safe to go back in the water until the chlorine level goes back below about 5ppm. 

The skimmer is the first line of defense against particles and larger objects getting into the spa plumbing such as leaves or playing cards.  The cartridge filter is sometimes located under the skimmer as the next line of defense for finer filtration.

Sodium Bicarbonate
Increases the total alkalinity of spa water

Sodium Dichlor
This type of chlorine is most often used in hot tubs in the form of either pucks or granular content. Dichlor is preferred over Tri-chlor that is used in swimming pools, but don't use tri-chlor pucks in hot tubs.

Soft Water
Water with low levels of ions and dissolved calcium is considered soft water. Water softeners also produce this type of water. It is not recommended for use in hot tubs.

Spa Pak - Spa Pack
The electronic control system that contains the circuit board and wiring along with receptacles to plug in the external spa components such as pumps, ozonators, heater, blower and lights.  The control panel plugs into the spa pak/circuit board.

Suction grates or covers are used in the spa footwell to protect the plumbing from anything that could be sucked into the lines when the pump creates suction to pull in water through the suction fitting.  Suction itself is created through the removal of air which allows fluid to force its way into the void.

This is an alternate method to kill bacteria and microorganisms to a shock treatment.  This type of more drastic chemistry is used to purge and super-clean such as when purchasing a used hot tub.  It is not used in day to day maintenance because you can't use the spa after that for quite awhile.   Basically, the main property of superchlorination is to remove the ammonia compounds of chlorine/smelly water and has a side benefit of combatting algae.

t spa termsTest Kit
Instead of test strips, some prefer to use test kits which are made up of phenol red and other chemical solutions with a color chart to test pH and sanitizer levels as well as alkalinity. Pool owners rely more on test kits.  Hot tubs are easier to test with test strips that usually come in a vial of 50 strips.

Test Strips
Water test strips for hot tubs can measure different things about the water including pH, chlorine or bromine levels and total alkalinity. There are also test strips for sodium bromide (for systems with bromine salt systems) and other strips that will test for water hardness or bacteria test strips.  Basically they are just dip and read. Compare the color on the strip with the definitions on the bottle or container the test strips came in. Adjust the water so that pH is within the 7.2-7.6 range by using spa up to increase pH for low readings and pH minus for pH readings that are too high.

An electronic, electro-mechanical or mechanical thermostat regulates the water temperature by using a sensor to measure current temperature and switch on or off the electrical output to the heater to call for heat if needed.

Titanium Heater
Titanium is used in place of incoloy heater elements and supposedly lasts longer.

Topside Control Panel
The control panel features buttons and sometimes knobs that control various spa functions from the top-side (mounted to the top edge of the hot tub) so that bathers can control the functions from within the spa or standing next to the spa. Some digital displays are even reverseable so they can be read inside or outside the hot tub.

Total Alkalinity (TA)
TA is read in parts per million (PPM). It measures the water's resistance to change in pH. TA is the amount of alkali (not alkaline) made up of bicarbonates, carbonates and hydroxides.  Stable pH means it is more resistant to swings which result in having to do more frequent chemical adjustments. The Total Alkalinity scale is in parts per million (ppm) and goes from 0 to 400. Suggested total alkalinity range for hot tubs is between 80-140 ppm.  If alkalinity is low, pH can fluctuate wildly and be hard to keep under control. If alkalinity is high, changing pH becomes very difficult.

Total Chlorine
The sum of combined chlorine and free chlorine.

Total Dissolved Solids (TDS)
A measure of the amount of material suspended in solution in hot tub water.  This can include metals and carbonates. Having high total dissolved solids in the water can damage equipment due to corrosion and also cause eye and skin irritation. This can even assist algae bloom. Basically TDS is everything in the water that is not the water itself including organic compounds and chemicals. If TDS gets above 3,000 ppm (parts per million), then problems are likely to occur with the water quality.  Adding chemicals does buildup TDS, so that is why over time we must drain and refill the spa and start over fresh. The best solution is to partially or completely drain and refill the water. Even huge swimming pools need to have the water drained every 3-5 years because of TDS buildup.

This form of chlorine tablet is used in swimming pools but not recommended for hot tubs as it can damage the spa shell and equipment. Use di-chlor granular chlorine or tablet form chlorine in hot tubs.

u hot tub termsUltra Violet (UV)
Ultra Violet light is one type of ozonator used to purify spa water.  The other main type is a corona discharge ozone generator.  UV light is also a part of the light spectrum and is a type of electromagnetic radiation transmitted in waves with frequencies of about 8 × 1014 to 3 × 1016 cycles per second, or hertz (Hz), and wavelengths of about 380 nanometers (1.5 × 10−5 inches) to about 10 nm (4 × 10−7 inches).  If you are still reading this after that last line, then you are a greater scientist than I and should go relax in the hot tub - you are taking this glossary way too seriously. One interesting tidbit about UV though is that only about 10% of sunlight is UV and only about 1/3 of that actually reaches the ground on Earth.  Protect yourself from overexposure to UV (sunburn) with a good sunscreen. Yes, you can get a sunburn sitting in the hot tub.

v spa terms

Venturi is the reference to air being introduced into the water stream to increase apparent water flow from the spa jets. The venturi or air connection is also used to introduce ozone from the ozonator into the spa water.

The spa pump housing that is the chamber for the impeller.

w spa terms


The part of the filter system that automatically adjusts to the water level. A weir door is a flapper that goes back and forth. Some manufacturers have removed the weir door from top load filters because they impeded water flow too much.  A floating weir is the type of skimmer that can bob up and down in the water and adjust to water level.


xyz spa termsXylophone, Yak and Zebra - confounded, there aren't currently any hot tub related terms for X, Y and Z - but if one comes up, we will surely list it here.



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