What’s Best? Chlorine, Bromine, or Biguanide

by Tony Turbo.

If you have owned your spa for a while you’ve likely heard of several sanitation regimens you can use in your hot tub.  With the exception of some little-used systems, they are all based on either chlorine, bromine, or biguanide.

The rather popular silver ion systems, such as @ease SmartChlor®, The Frog®, & Nature 2®, are based on either chlorine or bromine.  Also popular, salt systems are based on either chlorine or bromine.  The most popular, dichlor (full name: Dichloro-S- Triazinetrione) is a chlorine-based system.  So, let’s dive into these common spa sanitation regimens.

Halogens versus Biguanide

Both chlorine and bromine are member of the halogen group of elements.  In addition to being highly effective sanitizing agents they are also oxidizers.  Oxidizers, which include ozone and nonchlorine-based shock that you may also be using in your spa, remove biologic waste materials in your spa water.  Oxidation is an essential function in maintaining clear, clean, safe water in your spa.

Biguanide, in contrast, is not an oxidizer itself.  Instead, biguanide systems use hydrogen peroxide as an oxidizer.  The 2-punch capability that chlorine and bromine have to both sanitize and oxidize is one of the reasons these systems are, by far, the most popular spa sanitation regimens.

Though biguanide is a single system, there are many halogen-based spa sanitation systems.


Dichlor is actually a nearly 50 / 50 combination of chlorine and cyanuric acid (CYA). It is likely the most popular spa sanitation regimen as its simple, effective, inexpensive, and relatively easy to use. However, many alternatives exist because:

  1. Some people find chlorine harsh on their skin.
  2. It requires regular and frequent addition to your spa water.
  3. The chlorine smell can be objectionable.
  4. It’s very important to keep your spa water pH in the range of 7.2 – 7.6.
  5. It requires a drain & refill of your spa at least every 4 months and more often if you are a frequent spa user

By the way, NEVER use another version of chlorine called Trichlor in a spa. Unlike dichlor, trichlor is highly acidic with a pH around 3.0, Trichlor can damage (more like will damage) your spa shell and other components in your spa.


Bromine spa sanitation comes in two forms.  Granular bromine or tablets are the most common.  Though must less common than chlorine systems, bromine salt systems are also available, primarily from two manufacturers.  Proponents of bromine will focus on:

  1. Though still very effective as a sanitizer, bromine is gentler than chlorine.
  2. Very little noticeable odor
  3. Though you should keep your pH in the 7.2 – 7.6 range, unlike chlorine, bromine remains a very effective sanitizer even when this pH is not maintained.

And the downside to bromine?

  1. Chlorine is generally more effective when dealing with high sanitation loads.
  2. If you are using granular bromine or Brom Tabs, you must add them to your hot tub frequently – and not forget.
  3. Though not a huge issue, bromine is somewhat more expensive than chlorine.

Silver Ion (Ag) Based Spa Sanitation

Though the silver ion-based spa sanitation regimens all like to focus on the “Ion” story, they are all based on halogens, either chlorine or bromine. Though silver ions are an effective sanitizer (eye drops contain Ag ions), they are also very gentle and not adequately effective is dealing with the sanitation loads in a pool, and particularly not in a hot tub, unless they are augmented with a stronger sanitizer. For this reason, the EPA does not approve any ion-based system that is not combined with a halogen.
Silver ion-based systems are quite popular however because:

  1. They often require considerably lower levels of chlorine or bromine.
  2. Outside of biguanide & salt-systems, they generally are the least harsh on your skin.
  3. Though they generally are two-part systems, they require replacement much less often than other systems, other than salt-based systems.

The downside to Ion-Based Spa Sanitation?

  1. A bit odd, but because they require less attention, you may forget to replace the cartridges when they are empty.
  2. They are more expensive than dichlor or granular bromine.
  3. The chlorine-based systems require keeping pH in the 7.2 – 7.6 range.
  4. Perhaps less eco-friendly as you throw away a fair bit of plastic with each cartridge replacement.

Salt System Sanitation

The largest manufacturer of hot tubs has been promoting their salt system sanitation for close to 10 years.  They are the only major manufacturer to do this, but salt systems do have their advantages, notably:

  1. You generally replace your spa water once a year, rather than 3 – 4x a year.
  2. Though the salt level is too low to taste, with a concentration in the 1,500-ppm range, it will both make the water and your skin feel softer.
  3. It’s pure chlorine (or bromine in the case of some smaller manufacturers).  There are no other chemicals in the water other than those used to maintain the proper pH range.

The downside?

  1. Salt systems do not work well in situations with a high sanitation load.
  2. They are not inexpensive, generally on par with ion-based systems.
  3. The chlorine-based systems require keeping pH in the 7.2 – 7.6 range.
  4. One might argue that, somewhat like ion-based systems, they are less eco-friendly as you replace & throw away the system’s electrode cartridge 3x a year with the largest manufacturer’s system.


Biguanide systems operate in an entirely different manner than halogen- based systems.  As such, they are also totally incompatible with both chlorine and bromine.  Should you wish to convert from either of these to biguanide you MUST thoroughly clean your spa of any chlorine or bromine residual first.  That said what are the advantages to biguanide as a spa sanitizer?

  1. They are very gentle.  If you have skin problems, you may find biguanide is your only alternative.
  2. That’s really the only advantage, but that may be very important to you.

And the downside to biguanide?

  1. Also, rather expensive
  2. It works, but you must follow directions exactly.
  3. If directions are not followed exactly, water problems rarely seen with halogen-based systems can become a problem.

What Should You Choose?

You probably know what I will say.  It depends on what’s important to you but let me help.

  1. If you want the latest & greatest technology, then go with a salt-system.
  2. If you want lower levels of chlorine or bromine, then go in this order from most to none.
    1. Salt systems
    2. Ion-based systems
    3. Biguanide
  1. If you want inexpensive, tried & true, go with dichlor.
  2. If you have a high sanitation load (you and your friends use your spa every weekend), go with dichlor.
  3. If you want inexpensive, no chlorine, and you won’t have a high sanitation load, then go with bromine.

Thanks for reading,
Tony Turbo

Thanks for reading,
Tony Turbo

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