Hot Tub Chemicals Safety Guide

Hot tub chemicals vary with respect to their effectiveness in oxidizing and reducing microorganisms as well as their impact on your health.

This guide will demystify and provide comprehensive information to help you -- an owner of a hot tub to better understand the chemistry and treatment of water.

As a hot tub owner you are most likely using chlorine bromine or some alternative to chlorine to treat your tub water. Chlorination is one of the most commonly utilized methods for treating water.

This guide will provide answers to frequent questions hot tub owners ask including those related to ph, alkalinity, water balance, hardness and general water chemistry and many more -- all factors that are required to treat tubs against algae, mold spores, bacteria and viruses.

List of the Best Hot Tub Chemicals And Their Use

  • Chlorine in liquid or tablet form
  • Balancing water pH is necessary to ensure proper efficacy
  • Bromine is sold in powder of tablet form
  • Lithium comes in powder form
  • Hydrogen peroxide (Peroxysan) dissolves to form water and oxygen...especially recommended for health safety in float pods / float tanks

Sources of Hot Tub Chemical Contaminants In Spas

There are sources of contaminants that react chemically that may surprise bathers. These can react in water especially when the pH is not neutral or pH of 7. So bathers should be conscious of the potential risks when entering their hot tub.

Unsuspected sources of chemical reactions:

  • Urine
  • Sweat
  • Dirt
  • Lotions
  • Soap Residue

Other sources could include disinfectants and their byproducts that react with bathers skin.

Sources of Hot Tub Reactions With Bathers

Common Hot Tub Water Conditions

  These are some of the most common hot tub and spa water problems.  
1. MoldsWhite mucous like coating surfacesCan cause respiratory issues. Found on pvc surfaces, piping etc. Resilient to halogens like chlorine and bromine
2. AlgaeTurns water green Attracts bacteria which can cause illness
3. BacteriaNo visible signsCauses folliculitis and potentially dangerous Legionnaires disease
4. VirusesWater can be a vector.Persons infected with viruses such as STD's can transmit viruses through water.

Monitor Hot Water Temperature

Hot water temperatures in your hot tub can provide a soothing, calm and relaxing environment after a hard day at work.

But did you know that high water temperatures favour the growth of microorganisms? Hence it is important to maintain your spa free of these water borne organisms using effective oxidizing and reducing chemicals.

Weekly testing and monitoring the state of your tub and vigorous treatment with chemicals is highly advised. ​

My Water Is Too Cloudy

If your water is murky and isn't crystal clear then these might be the cause:

  • Test with a water chemistry test kit and determine if there is a low  oxidizing or reducing chemical concentration.
  • This condition could be due to minerals in the water. Filter your water with a hand held filter.
  • Check your spa filter and ensure it is functioning properly.
  • Your water may be out of balance. Check the ph, alkalinity and calcium in your hot tub.
  • Check the total dissolved solids including, charged ions, salts and metals. It is recommended to have no more than 500mg / litre of water. 

My Water is Green

  • Pollen deposited in the water can cause your hot tub to turn green especially with low concentration of hot tub chemicals. Vacuum and filter your tub should clear it up.
  • Low cleanser agent can cause your hot tub water to turn green. Ensure you maintain the proper concentration of chemicals in your water.
  • Another cause of green water is copper which can be introduced from the use of inexpensive algaecides.

The presence of algae will generally appear dark green and most likely you will not be able to see the bottom of your spa. If the colour appears light green then most likely the issue is contamination by metals. If no metals are present than the pool or spa is contaminated with pollen.

Treating Light Green Water​ From Metals

If the water is clear and then shock treated which results in the appearance of light green water colour, then that is clear sign of the presence of metals.

Treating your water is best conducted by shocking the spa with an oxidizing and reducing agent as well as a high quality algaecide -- 40% poly-quat strength. Your hot tub will no longer be green but will take on a cloudy, murky appearance.

Turn on the filter and let it run for 24 hours. While the filter is running, scrub the tub lining to rid it of the algae's protective covering.

Causes of Foamy Water

Foamy water is usually not a condition any cleansing chemicals added to the water. This condition is usually attributed to various cosmetics and body oils in alkaline water. These conditions can adversely affect the efficacy of your pool and spa chemicals.

  • Reduce or eliminate the use of cosmetics while bathing.
  • It is recommended to shower prior to entering your spa

How to Stop Water Odours

Does your water smell like a wet dog, dirty socks or just smells bad? This is sure sign that bacteria is lurking in your spa in some hidden area such as the plumbing, filters, equipment and areas that are generally less exposed to the chemicals you use. 

If your hot tub has been neglected for sometime, bacteria populations can propagate giving your spa a pungent odour.

The best course of treatment will be to shock your tub water with a high concentration oxidizer or reducer.​

Sanitizers for Treating Your Water

Microorganisms can thrive in water especially when the temperature at levels that are comfortable for bathers. Therefore it is important to use an oxidizing or reducing chemicals that lower the microbial population to levels that are deemed safe. The most commonly used pool disinfectants are chlorine and bromine that are classified as halogens. 

family hot tub


Chlorine is considered an effective oxidizer against bacteria. Yet, the concentration of chlorine required to effectively mitigate microbial growth can to some extent be an irritant to bathers' mucous membranes, e.g. the eyes and nose with prolonged exposure. In addition respiratory problems such as asthma have been reported.

There are safer alternatives to chlorine and bromine which do not react with hot tub users eyes, nose and respiratory tract.

Chlorine Concentrations and Application

Chlorine usually comes in the form of hypochlorous acid or hypochlorite. Potenz Hydrogen (ph) and alkalinity are important factors to consider when determining chlorine potency. Using a drop kit will help to these levels. The lower the presence of calcium, water hardness, (CH), the higher the alkalinity, (TA), and acidity, (pH) need to be. Greater TA will result in potential scaling while in contrast, greater pH can potential damage your spa's equipment due to corrosion. A higher degree of calcium should be treated with a water softener.

  1. Test your water to ensure it is balanced, that is, the ph is between 6.8 and 7.8.
  2. A neutral ph 7 will provide 70% of free chlorine in your spa which is the most efficient concentration of chlorine in your water in terms of efficacy and cost.
  3. Calcium, which determines the "hardness" of your water plays a significant role in chlorine uptake. The harder your water the less effective chlorine will be. Therefore, ensure your water is effectively clear of calcium minerals.
  4. Sunlight UV rays can cause chlorine to dissipate more quickly. Stabilizers such as cyanuric acid are usually added to chlorine in products like Dichlor.
  5. As a general rule you should use 7 ppm of free chlorine per 350 gallon tub per person per hour. Alternatively measure 1 cup full strength Peroxysan of 35% cup H2O2 for every 500 gallons of water.
  6. Make sure to wear goggles and gloves when working with this chemical.


Bromine is considered a safer alternative to chlorine. It is generally less of an irritant to eyes, nose and respiratory tract. That is why many people use bromine as an alternative to chlorine. 

While bromine is preferred as explained above, it is less resistant to the effects of the ​sun's UV rays. However, due to bromine's bigger atomic structure, it is more effective in killing bacteria and viruses than chlorine. Chlorine on the other hand is more effective in the destruction of algae. 

Bromine is less susceptible to swings in pH in comparison to chlorine. ​

Salt Water Treament

Some people believe that salt water treatment systems are less harmful than chlorine and bromine. This is actually a misconception.

The chemistry of salt causes a reaction resulting in producing chlorine in water which makes salt water treatment equivalent to chlorine. Salt as a sanitizer involves a greater sequence of steps in sanitizing your spa which make it harder with which to work. It is always best to balance your water for pH and concentration of hot tub chemicals.

Balancing Your Spa

An important factor to be aware is that bather load and frequency that affect the balancing of your water. In essence, the average number of bathers and the frequency with which bathers soak per day in a hot tub will be a bellwether for determining bacteria load and water conditioning. Balanced water with optimal pH, TH and alkalinity will increase the efficacy of  sanitizers that oxidize or reduce organisms.

Your water could be fine till bathing habits change. Ultimately this would mean that more rigorous water testing and sanitizing would be required to ensure safety from increased bacterial load.

Follow these steps when using bromine to cleanse your water.

  1. Use a test kit to verify CH, TA and pH of your hot tub or pool.
  2. If your water is too acidic then you will need to balance the water.
  3. If your water has contaminants (cloudy, murky) then you will need to shock treat your spa.
  4. In general, you will want to maintain a 3 to 5 ppm of bromine and test weekly.
  5. Make sure to wear safety goggles and gloves while working with all chemicals.

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