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Hot Tub Water Quality – Key for Spas and Hot tubs

Mar 23, 2016 | Hot Tub Water Quality

Hot Tub Water Quality has been the topic of countless articles and debates concerning the treatment of not only spa and hot tub water but pool water as well. The goal is to first maintain safe conditions for the bathers and secondly protect the equipment used in operating these units.

Industry regulations by The International Aquatic Foundation (IAF) and National Spa & Pool Institute (NSPI) have developed a set of guidelines for chemical maintenance of water quality using certain chemical compounds to maintain sanitary conditions of the water we soak and swim in. But what is important to understand is that even though certain levels of chemical exposure are considered safe, excessive exposure to some of these substances may have an adverse effect on your health. This is why diligence should be used in maintaining your waters quality. You may not need to treat your water but once a week, but personally I like to check the levels of sanitizers at least every other day. However, during periods of high bather load, then daily checks will be prudent.

Water quality varies widely across our country, from pure pristine water of mountain streams and springs, to polluted hazardous water that you should not drink or be exposed to. Your hot tub water quality can be affect just by your water source. Just look at the recent fiasco with water in Flint MI. These people we exposed to unsafe water conditions just because some politicians thought they could make themselves look good by saving a few bucks.

I’ve seen many pool and hot tub owners unknowingly sacrifice safety in an effort to save as few bucks as well. My advice, don’t do it. Don’t be penny wise and pound foolish, especially when it comes to your health. Maintaining your waters quality and sanitary condition doesn’t have be expensive. Maintaining recommended sanitary levels of certain compounds will actually cost you less than trying to correct conditions that have gotten out of limits.

So what are typical hot tub water quality chemistry parameters and levels we look at for spa and hot tub water

They are:

  • Total Hardness – The proper “hardness” level helps keep water from causing corrosion or scaling. Ideal level is between 250-500ppm (parts per million).
  • Total Chlorine – Knowing the “total chlorine” level helps you to determine when to “shock” (when compared to the “free chlorine” level). 1-3ppm
  • Total Bromine – Another type of disinfectant primarily used in spas and hot tubs. 2-5ppm
  • Free Chlorine – when free chlorine is at ideal levels, your water will stay sparkling clean! (spas) 3-5ppm, pools 1-3ppm
  • pH – Maintaining proper pH levels helps prevent water from causing corrosion or scaling. 7.2-7.8ppm
  • Total Alkalinity – Correct “alkalinity” levels prevents sudden pH changes that could led to corrosion or scaling. 80-120ppm
  • Cyanuric Acid – proper levels of “Cyanuric Acid” helps protect against chlorine loss caused by sunlight. 30-100ppm (ideal 30-50ppm)

Water chemistry parameter chart

So let’s break this down in a little more detail for these chemicals.

The most popular type of disinfectant used for hot tub water quality is chlorine. The amount of chlorine that your hot tub or pool requires to eliminate contaminating materials from the water is called chlorine demand. The chlorine that is active and able to sanitize and oxidize contaminates in the water is referred to as “free chlorine” residual. Chlorine that has already used up its ability to sanitize by reacting with contaminants is called combined chlorine. Periodically you need to add more chlorine to your water to maintain the optimum level of this sanitizer to react with new contaminates and maintain hot tub water quality.

When the free chlorine residual has used up its sanitizing ability, it becomes combined chlorine. An over-abundance of combined chlorine can cause eye irritations and strong, sometimes offensive, chlorine odors. Most people think that there is too much chlorine in the water when they smell this strong odor and believe the hot tub water quality is poor. However, just the opposite is true. All the free chlorine has combined with contaminants and has created those strong smelling combined chlorine products. If your total chlorine test strip reading is higher than your free chlorine test strip reading, you need to superchlorinate or shock treat your pool. Superchlorination or shock treatments are required more frequently when pool or spa water temperatures are high or heavy swimmer loads occur.

Superchlorinating, or shock treating, your pool or spa means adding enough chlorine to raise the free chlorine residual to 10 ppm for at least 4 hours. Alternatively, shock treating can be carried out with potassium monopersulfate (non-chlorine shock treatments). Non-chlorine shock treatments will consume the organic contaminants, but will not sanitize.


Bromine is another popular type of disinfectant, primarily used in spas. Bromine is more effective in high temperatures and higher pH ranges associated with spas. Additionally, combined bromine does not produce the offensive odor that combined chlorine does. However, bromine is not ideal for outdoor pools and spas because bromine is not stable in sunlight (UV). Bromine is very quickly degraded by strong sunlight until no disinfectant remains, creating an unsafe swimming environment. Therefore, bromine is only used in indoor pools and hot tubs (or in hot tubs that remain covered when not in use). Unlike chlorine, the combined form of bromine is still an effective sanitizer. Whereas combined chlorine is chlorine that has used up its sanitizing ability, combined bromine is still capable of sanitizing and disinfecting. Therefore, Total Bromine is measured to indicate the sanitizer residual. An appropriate level of bromine in the water will help to ensure the water remains clean and clear.

Total Alkalinity and pH:

Total alkalinity measures the amount of alkaline substances (primarily, bicarbonates and carbonates) in your water. Alkaline substances buffer your water against sudden changes in pH. It is important to prevent pH changes that can cause scaling or corrosion of metal fixtures. The total alkalinity is in the right range at 100 to 120 ppm (parts per million) if sodium dichlor, trichlor or bromine is being used as the sanitizer. Total alkalinity levels of 80 to 100 ppm are considered to be in the right range if calcium, sodium, or lithium hypochlorite is being used as a sanitizer. pH refers to the intensity of acid or alkaline materials in your water. pH intensity is measured on the pH scale, a numerical scale extending from 1 (extremely acidic) to 14 (extremely basic). A pH of 7.0 is considered neutral. The right pH range for pool and spa water is 7.2 to 7.8, with an ideal range of 7.4 to 7.6. pH levels greater than 7.8 can cause swimmer discomfort (skin and eyes), produce scale on the pool or spa and equipment, and reduce the sanitizing action of chlorine. pH levels less than 7.2 can also cause swimmer discomfort and cause corrosion of pool or spa fixtures and equipment.

Cyanuric Acid:

Cyanuric acid, also called “stabilizer” or “conditioner,” makes chlorine more stable when exposed to the sun’s ultraviolet rays. It is like sunblock for your sanitizer, preventing it from degrading as quickly as it would otherwise. Without cyanuric acid, your chlorine level can drop from the ideal range to zero in less

than two hours. On the other hand, if cyanuric acid is too high, it can cause a high level of total dissolved solids (TDS), and cause chlorine to be inefficient. Two types of chlorine compounds, dichlor and trichlor, already contain some cyanuric acid. The level of cyanuric acid will build up with the continued use of either of these sanitizers. If using any other form of chlorine, you will need to add cyanuric acid separately in order to stabilize the chlorine. The acceptable level of cyanuric acid is 30 to 150 ppm (except where 100 ppm maximum is regulated by the health department), with an ideal level of 30 to 50 ppm (mg/L).

Your waters make up:

Hot tub water reflection

The last thing I want to cover on spa and pool water is the waters actual make up. In the beginning of this blog I mentioned water can come from pristine streams and springs or from other more polluted sources. Depending on where you live and what your water source is can lend to your water having any variety of minerals in its make-up. Some of these minerals can be completely harmless in your pool or hot tub water and some of them can make it very difficult to maintain water chemistry balance.

You’ve likely heard the terms “soft water” and “hard water”, as conditions many areas of the country deal with. Soft water isn’t as usual of problem as dealing with hard water can be. Some hard water conditions require treatment of incoming water before it’s sent through a home’s plumbing system. This is because a condition of calcium build up may occur which can be damaging to a home’s water appliances. A home may use a whole house purification system or simply pass water through a container filled with rock salt to soften the water. In our area, Culligan Water Softening systems are popular, but they are just one of many. Hard water can have an adverse affect on hot tub water quality, so have your water tested this way you will know what you will be dealing with.

How this relates or effects spas, hot tubs and pools is important to understand. This is because water used to fill these units may contain minerals that make excessively difficult to maintain proper water chemistry. In these cases, water may have to be purified before the filling process begins to alleviate the impact these minerals have you your water’s chemistry.

One simple step you can take before you undertake keeping your water’s chemistry balanced, is to have it tested. There are a variety of tests that can be performed on water from its potability, (is it drinkable) to the amount and concentration of minerals it may contain. These tests will be important for you to have done if you suspect or if you know the water in your area could have adverse effects on maintaining proper water chemistry. Ignoring water testing when you know your area could have issues can lead to expensive equipment repairs, so spend a few bucks on this first.

Wrapping it up!

I hope this article has been helpful to you in clearing up some of the mystery on hot tub water quality and water chemistry as it relates to pools and spas. Feel free to contact me for more specifics about treatment equipment I typically supply my spa and hot tub building customer.

Gene Trumbull
Custom Built Spas

Call With Questions (860) 571-8440



Remember, my Mission is to help you, as my customer, build a beautiful hot tub of your own! I can show you how to build Spas, Hot Tubs, Swim Spas, Plunge Pools, Cocktail Pools or Exercise Pools at incredibly affordable prices! Everything you need to know is outlined in my series of easy-to-follow books and videos that cover a simple, step-by-step process that I’ve developed and refined over the years.

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