The Chemistry of Hot Tub & Spa Water Care

Balanced spa water that is maintained to be clean, healthy, and sparkling clear provides the most enjoyment for your soaking experience and greatly increases the life of your equipment. You will find a wealth of information on hot tub and spa maintenance and water care on this page.

The Basics :

SANITIZE: A disinfectant level of 3-5 parts per million (PPM) bromine or chlorine is necessary to continuously kill bacteria. Bromine, unlike chlorine, is effective even after disinfecting. It has a less offensive odor and causes less irritation than chlorine. It's more pH stable, and easier to maintain in the proper level by using tablets in a convenient floating dispenser. However, being more stable than chlorine it can be more difficult to remove the odor from your skin. Even if your spa is equipped with an ozonator, you should still use a sanitizer and shock treatment.

SHOCK: Shock treatment is best accomplished by the addition of an oxidizer to the water to break down organic contaminates. These contaminants include: dirt, soap films, oils and perspiration. Filters do not always trap these and other very small particles. If they are allowed to remain in the water, they can provide a food source for bacteria and algae. Regular shock treatments will eliminate them.

pH:  When the mineral components of spa water are in correct proportion to one another, the result is "balanced" water. When balanced the water is neither too alkaline (pH above 7.8) which causes destructive scale buildup on equipment, nor too acidic (pH below 7.2) which will corrode metals and cause costly damage to spa pumps, seals and heaters. Balanced water has a more pleasant feel to the skin, and allows your sanitizer to work more effectively.

TOTAL ALKALINITY: Total alkalinity (TA) is also important. It is the measure of all the alkaline material in the water. It is really an indicator of the ability of the water to resist changes in pH. This is known as the water's buffering capacity. The ideal range for TA is 80-100 PPM.

CALCIUM HARDNESS: Depending upon where you live, you may have what is commonly referred to as "hard" water: water with high levels of dissolved calcium, or "soft" water with relatively low levels. There is some latitude in acceptable ranges for dissolved calcium. Generally, a range of 150 to 300 PPM (or even somewhat higher) is acceptable.


Adjusting spa water for proper pH, Total Alkalinity, and Calcium Hardness is very important, but really not that difficult!

Balancing Your Water :

If you are new to this subject, please refer below to the "The Definitions of Water Terms" first, for a basic understanding.

For testing and adjusting your hot tub spa water, you should have these basic supplies on hand:




Always test for total alkalinity (TA) first, using test strips or kit. The acceptable range is 60-180 PPM. If below 60 PPM, add Spa Up until a reading of about 100-120 PPM is reached. If above 180, add Spa Down until a reading of about 120-140 PPM is attained.


Now check for proper pH level. The acceptable range is 7.2 to 7.8 . If below 7.2, add Soda Ash until a reading of about 7.4 is reached. Spa Up may also be used, but keep in mind that Spa Up will also raise the total alkalinity, so if the TA is already high, you must use Soda Ash. If the pH is above 7.8, add Spa Down until a reading of about 7.6 is reached.

Once pH adjustments have been made, you can lock pH into balance by adding pH Balance and there will be no need for further adjustments for at least 3 months! Note: pH holding products are not recommended in areas with high water hardness (above 500 PPM).


The ideal calcium hardness level for hot tub spas is 200-400 PPM. If your level is below about 150 PPM, some erosion of equipment parts can occur. Low hardness can be corrected with Hardness Up.

Note: addition of Calcium Booster is not recommended if you are using pH Balance or other pH holding products.

Troubleshooting :


Cloudy water Filter problems Test all chemical levels with an accurate test kit and make the appropriate adjustments.
Skin irritation Improper pH or Total Alkalinity levels Test all chemical levels and make the appropriate adjustments.
Eye irritation Low sanitizer levels or excess 'combined chlorine.' Test all chemical levels and make the appropriate adjustments. Shock your spas water  with Renew or Oz tabs per instructions.
Algae growth Low sanitizer levels Shock your spas water with Renew or Oz tabs per instructions. Brush the spa walls. Run the filter for a 24-hour period to increase distribution of sanitizer and add Spa Algaecide.
Excessive foam Buildup of body oils or cosmetics Generally there will also be a water line around the top of the spa (see next problem). If no water line is present you can try using Spa Foam Down to break up the contaminants and then Spa Bright and Clear to help filter them away. If a  water line is present the spa should be drained and cleaned. Either way, the filter should be thoroughly cleaned by soaking over night in Spa Cartridge Clean. An oil absorbing sponge such as The Dirty Duck can help in preventing this in the future.
Excess organic contaminants Some organic matter is prone to causing foamy water as it breaks down in the filter (maple leaves especially). Generally using Spa Foam Down to break up the contaminants, then Spa Bright and Clear to help filter them away followed by thoroughly cleaning your filter will clear up the problem. It may however be necessary to drain and refill your spa if the foaming is quite excessive.
Low Total Hardness Test water with a Total Hardness Test Kit and if necessary increase with Calcium Booster.
Excess bromine Generally the water will also have a green tint to it. The spa will need to be drained and refilled, and the bromine feeder adjusted correctly
Oily water line Body oils, dirt, soaps Scum line may be able to be removed with paper towel. Alternating weekly between Spa Bright and Clear and Scum Gone along with frequent filter cleanings usually eliminates this problem.
Unstable pH Low total alkalinity levels Test total alkalinity levels with an accurate test kit and if necessary increase with Spa Up.
pH resistant to changing High total alkalinity levels Test total alkalinity levels with an accurate test kit and if necessary decrease with Spa Down.


The Definitions of Water Terms

Some common, and not-so-common terms, briefly defined to help beginners and seasoned hot-tub users gain a better understanding of "spa science". Product references, where applicable, are noted in parenthesis.


Chemicals such as sodium bisulfate ( Spa Down) or muriatic acid used to lower pH or alkalinity.

Microscopic aquatic plant life which can grow on spa surfaces or float in the water. Although harmless to bathers, algae discolors the water and indicates improper sanitization.

A chemical used to kill algae and prevent the re-growth.

See Total Alkalinity.

Microscopic organisms continuously entering the water via bathers, airborne dust, etc. Without proper sanitization hot tubs and spas are the ideal breeding ground for bacteria, many of which can cause disease or infection.

Balanced Water
Water that is neither corrosive nor scale forming. Water with the proper relationships of pH, total alkalinity and calcium hardness is said to be balanced.

A chemical which raises pH and/or alkalinity when added to the water (pH UP or Spa Up).

Bather Load
The number of individuals using a pool or spa in a 24 hour period. This is the primary source of bacterial and organic contamination.

Break Point Chlorination
The process of shocking the water with significant quantities of chlorine to oxidize all contaminants and organic wastes and leave all remaining chlorine as free chlorine.

A floating device which holds bromine tablets and dispenses a metered amount of bromine sanitizer into the spa water.

The preferred sanitizing agent for hot tub spas that kills bacteria and algae. The tablet form of this product is dispensed using a floating brominator. The granular form is added upon spa startup (initial filling) to establish an immediate bromine reserve.

A chemical that resists pH change in spa water, such as sodium bicarbonate ( Spa Up).

Calcium Hardness
A measure of the amount of calcium dissolved in water. Water with low hardness can lead to corrosion of metal parts. Total Hardness Test Kits are available for checking hardness levels.

A naturally occurring polymer (pronounced KY-tin) found in crab and lobster shells

Chlorine ammonia compounds formed when chlorine reacts with organic contaminates in the water. Chloramines are not effective as sanitizers and are responsible for eye and skin irritation as well as b chlorine odors.

A sanitizing agent that kills bacteria and algae.

The etching away of metal fixtures and pump seals due to improperly balanced water.

Cover Protectant
A special formulation for vinyl spa covers which prevents deterioration caused by sunlight and weather.

Cover Removal Device
A device to aid in the removal, storage and reinstallation of insulated spa covers.

To kill and inhibit growth of harmful microorganisms spa water through the use of a sanitizer such as chlorine or bromine.

Dry Acid
A granular chemical, sodium bisulfate ( Spa Down) used to lower the pH and/or total alkalinity.

Biodegradable proteins which break-down oils, films and digest scum in spa water ( Scum Gone.

Filter Media
A pleated, porous synthetic fabric in filter cartridges, used to trap foreign matter. Filter cartridges must be cleaned regularly with filter cleaning compounds to maintain spa water quality ( Leisure Time Spa Cartridge Clean).

A compound which clarifies of "flocs" spa water by gathering small contaminant particles into larger globules, which then can be easily trapped in the filtering system.

Free Chlorine
The amount of chlorine available to kill bacteria or algae.

Hard Water
(See Calcium Hardness).

An alternative proprietary spa sanitizing system which does not require the addition of bromine or chlorine.

Non Chlorine Shock
An oxygen-based shocking compound, potassium peroxymonosulfate, (Oz). Non-chlorine shock is fast dissolving so it allows hot tub use just 15 minutes after application (see Shock).

Organic Wastes
Wastes such as body oils, perspiration and sun tan residues which bathers introduce into the spa. Most organic wastes will not filter out and must be broken-down by shocking with an oxidizer.

A test reagent used to test bromine and chlorine in pool and spa water in liquid test kits.

The process of breaking down organic wastes by the addition of a shocking compound ( Oz) to the spa water.

A scale of the relative acidity/alkalinity of water. The pH scale runs from 0 to 14, with 7 being the neutral midpoint. A pH reading of less than 7 indicates water which is on the acid side of the scale. A pH of more than 7 is on the basic (alkaline) side. In spas, the acceptable range is between 7.2 and 7.8.

pH Decreaser
An acidic chemical used to lower pH or alkalinity ( Spa Down).

pH Hold
A product which locks the pH of spa water into perfect balance for up to 3 months or until the next water change ( pH Balance). After setting initial pH, use of this product eliminates the need for continual pH adjustment.

pH Increaser
A base compound used to raise pH ( Spa Up).

pH Meter
A hand-held electronic device for instantly measuring the relative pH of spa water without the need for test strips or reagent solutions.

Phenol Red
Chemical reagent used for testing pH in the range of 6.8 - 8.4. Found in liquid test kits.

Parts per million. (Example: 1 cent in $10,000 = 1 PPM).

A compound such as bromine or chlorine used to kill microorganisms in spa water.

Calcium crust or buildup caused by unbalanced water. These mineral deposits forms on spa surfaces and clog filters, heaters and pumps. The regular use of stain prevention chemicals can prevent scale formation.

Scale & Stain Preventer
A product which prevents the formation of calcium scale and stains on spa fittings caused from copper and iron plumbing (Metal Gon).

Scum Digester
An enzyme product which breaks down body oils, soap film and lotion residues in spa water ( Scum Gone).

Addition of an oxidizer ( Renew or Oz) or superchlorinator to break-down the organic contaminates on which bacteria feed.

Soda Ash
Common term for sodium carbonate which is used to raise pH of spa water.

Sodium Bicarbonate
Commonly used to increase pH and total alkalinity of spa water ( Spa Up).

Sodium Bisulfate
Also known as dry acid, the chemical used to lower pH and total alkalinity of spa water ( Spa Down).

Soft Water
Water with very low levels of dissolved calcium. Can be corrected with calcium hardness increaser (Calcium Booster).

Spa Fragrance
Special perfumes designed to enhance the hot tub experience and overcome chemical odors. These are designed for spas, and will not alter water balance or clog filters ( inSPAration).

Application of large shock dosages of chlorine to destroy buildup of organic contaminates in water. The preferred alternative is to use a non-chlorine shock .

Test Kit
A set of chemical solutions and color references for testing pH, total alkalinity and sanitizer levels of spa water.

Test Strips
Easy-to-use dip strips for measuring the pH, total alkalinity and sanitizer levels of spa water. Strips are also available for testing water hardness levels.

Total Alkalinity (TA)
The measure in PPM of all the dissolved base/alkaline material in the water. The acid-neutralizing capacity of water which indicates its buffering ability, or resistance to fluctuations in pH.

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