Our hot tub chemistry for beginners article is a simple but comprehensive guide to maintaining your hot tub or spa pool. It’s not difficult or time-consuming to maintain a hot tub yourself. Please read this hot tub chemistry post and learn how to maintain your own hot tub or spa pool.
Hot tubs contain a relatively small volume of water which can quickly become dirty unless properly sanitized and filtered. The most important task is to regularly test the water with chemical test strips. Once an issue is identified get on to it quickly to prevent it becoming a larger issue. The effort required to prevent an issue occurring is always less than fixing a problem. If the water chemistry gets out of control you can always empty the tub and refill with freshwater.
Table of Contents
Hot Tub Water Chemistry
The chemical components of Hot Tub water are naturally linked together. Adjust one chemical component and it affects another. So you need to know about all the components to successfully balance the hot tub chemistry.
pH Scale
The pH scale is one of the central components to hot tub chemistry for beginners.
pH is a scale in chemistry to indicate the level of acidity or alkalinity of an aqueous (water-based) solution. The symbol pH means “power or potential of hydrogen”.
Strong acid is pH 0
Pure water, at 25C, is neutral at pH 7.
Strong base (or alkaline) is pH 14.
Spa & Hot Tub water should normally be between pH 7.2 and 7.6 which is slightly alkaline and never acidic.
Total Alkalinity
Total Alkalinity in pool water is the measure of all alkaline compounds dissolved in the water. It is a measure of the water’s ability to resist changes in pH by providing capacity to neutralize acid. The right amount of alkalinity helps to buffer your pool water from changes in pH.
In the swimming pool industry, total alkalinity is a measure of the dissolved carbonates and bicarbonates in water in parts per million (ppm).
The correct level of alkalinity depends on many other factors such as water hardness, pH and temperature.
Spa & Hot Tub water should have Total Alkalinity between 80 – 120 ppm.
Calcium Hardness
Calcium Hardness is the measure of all calcium compounds dissolved in the pool water.
The recommended level of calcium is as low as possible to minimize any problems with calcium type deposits forming on the pool surfaces or in the salt water chlorinator cell.
Calcium Hardness 200 – 400 ppm
Warning: Water sources from bores, dams and rivers can be high in mineral and organic contaminants resulting in faster mineral deposit formation and poor chlorine production. These water sources will require additional chemical treatment before the water is suitable for a swimming pool.
Stabilizer (Cyanuric Acid)
Cyanuric Acid (CNOH) is manufactured as a white, odourless solid compound and is most commonly used as a stabilizer for swimming pool & spa water. Chlorine is a highly reactive element and dissipates rapidly in water. The cyanuric acid binds to free chlorine in water slowing down the reaction of chlorine which extends the useful life of chlorine in the water.
On a hot summer day ultra-violet radiation can quickly burn off free chlorine from pool water leaving the water unsanitized and less safe for swimming. Adding the correct amount of cyanuric acid to water ensures the free chlorine in your pool or spa lasts longer and dissipates slowly keeping the water sanitized for a longer period.
If your hot tub or spa pool is sanitized with chlorine and exposed to the sun add stabilizer to the water.
The normal level of Cyanuric Acid (Pool Stabilizer) is 30 – 80 ppm
Do not add cyanuric acid to hot tubs or spa pools that are sanitized with bromine. Bromine is not able to be stabilized and is only recommended for spas and hot tubs because it would quickly burn off in the sun and it works well at the higher temperatures in hot tubs.
Chlorine
The highly reactive and oxidizing characteristic of Chlorine led to the development of commercial bleaches and disinfectants to sanitize bathrooms, hospitals and other public areas.
Use chlorine, in the form of sodium hypochlorite (NaClO), to sanitize swimming pool water. Sodium hypochlorite solution is unstable and rapidly decomposes releasing aqueous chlorine which kills bacteria, algae and other microbes in your pool water.
Keep the level at 3 ppm for maximum effectiveness in a Hot Tub.
Bromine
Bromine exists as a red-brown liquid at room temperature and is less reactive and a weaker oxidizing agent than chlorine. However, bromine is still a relatively reactive chemical and toxic.
Bromine works better and is more stable at higher temperatures than chlorine so it is commonly used in spa pools and hot tubs.
Bromine produces less chemical odor than chlorine which suits small water pools and spas or people who cannot stand the smell of chlorine.
Free chlorine has a short lifespan in the pool. Once free chlorine combines with contaminants it rapidly loses its chemical reactivity and will no longer work to sanitize the water, whereas bromine has a longer lifespan in the water and keeps the water sanitized for longer.
The main disadvantage of bromine is that it costs much more than chlorine. As a result pool owners prefer to use chlorine in a swimming pool but may use bromine in the spa or hot tub.
Shock Treatment
The term “shocking your pool” is pool industry slang language for super chlorinating your pool or hot tub. All it means is giving your hot tub an extra dose of chlorine. This ensures the water is adequately sanitized by killing bacteria, viruses and algae that may exist in the water.
Use unstabilized chlorine to shock a spa pool or hot tub.
Unstabilized chlorine is simply plain chlorine without added stabilizer.
Before you handle any chemicals make sure that you are using protective clothing and gloves. I recommend a mask and eye protection as well.
Normally, you can spread the shock around over the hot tub surface. Carefully read the manufacturer’s instructions to ensure you are applying the shock correctly for your hot tub or spa.
Shock treatments can cause the water to look cloudy for a few days. This is normal and will dissipate over the next few days as the free chlorine reacts to other compounds in the water.
If your sanitizer is bromine use a bromine-based shock treatment.
Hot Tubs Problems
Calcium Scale
Hot tub water can become saturated with calcium compounds that come out of solution and crystalize on surfaces and equipment. This process commonly produces a clear or white-looking lime scale build-up around the waterline but scale will also crystalize on the walls and steps.
Scale deposits can also form inside your plumbing, filter tank, water heater and chlorinator unit. When this happens clean these components otherwise they will operate with a reduced capacity or fail completely.
High calcium hardness, high pH and high total alkalinity cause calcium carbonate crystals to form on surfaces and equipment.
When a hot tub or spa pool has a lot of calcium scale the best way to clean it off the surfaces is to empty the tub to have easy access to the surfaces.
One way to remove scale is to perform an acid wash on the pool surfaces.
Add 3 cups of water to a bucket then 1 cup of hydrochloric acid to the water. Brush the acid wash on to the scale which will bubble and fume while dissolving the scale.
Brush the scale away and wash the surface with fresh water.
Please read our article on How to Clean Calcium Scale from a Pool
Metal Stains
Excessive metal ions in the pool water cause metal stains.
Pool Chemistry Lesson: When an atom (or group of atoms) gains or losses one or more electrons it becomes a charged particle, called an ion.
The water source causes metal ions. Water from bores, dams, streams, rainwater tanks and other sources may contain high levels of metals. These metals will raise your total dissolved solids (TDS) level and may cause problems sanitizing and balancing the water chemistry.
A corrosive water pipe or metal fitting in the water heater or filtration system will also cause metal ions to accumulate in the water.
Some brands of algaecide contain copper ions. Too much use of these algaecides over time can add copper to the pool increasing the Total Dissolved Solids.
Many metal stains can be chemically treated in the pool water. Other more difficult stains may require draining the pool.
Please read our article on How to Remove Metal Stains from a Pool
Foaming
Foaming water is another common issue for spa pools and hot tubs.
This is usually caused by contaminant chemicals from people such as shampoo, conditioner, cosmetics, deodorant, sunscreen, body lotions, soap residue, etc.
Draining and cleaning the hot tub or spa pool is the best way to eliminate foam forming in the water.
Replace the filter element to make sure it doesn’t happen again.
Green Water
Usually hot tub water has turned green because algae has begun growing in your hot tub and algae can only grow and flourish when the free chlorine in your tub has fallen below the normal level.
Note: Do not bath in green water. The water has become saturated with green algae such as Cyanobacteria which produces cyanotoxins that are dangerous and can cause sickness in all animals and humans.
Shock the hot tub and increase filtration to clear green water.
Please read our article on How to Clear Green Pool Water
Cloudy Water
The causes of cloudy hot tub water are:
- unbalanced hot tub chemistry
- a calcium build-up in the water
- a dirty ineffective filter
- not running the pump long enough each day to keep the water sparkling clear.
Check the water chemistry and re-balance the water.
If the water chemistry has too many problems it may be easier to drain the hot tub and refill with fresh water rather than spend money on chemicals.
Please read our article on How to Clear Cloudy Pool Water
Smelly Water
Chloramines are the chemical residue after chlorine has reacted and bound with dirt, sweat, sunscreen, urine, decaying insects, bacteria, algae and anything else that invades your pool water. If your pool water smells like bleach there are too many chloramines in the water. It’s time to shock the water.
Chloramines build up in the water making it easier for bacteria and algae to multiply and take over the pool. Shocking the pool water (super chlorinating) eliminates chloramines and keeps your pool water sanitized.
Conclusion
Hot tubs are a lot of fun and are in use all year round. Once you have read this hot tub chemistry for beginners article you should be able to put your hot tub maintenance worries behind you. Now you can enjoy the health benefits of the hot water.
Now you know more than the average hot tub owner. You are in a better position to care for your pool without spending money on unnecessary callouts to pool professionals.