How-To Guides | Chlorine Types & Which to Use

Not all Chlorine is Alike

Although we do not recommend packaged chlorine as a primary sanitizer in the hot water of spas, one type Dichlor Granular Chlorine is very good for occasional shocking and is a quick-dissolving form.

As a conventional sanitizer, bromine in tablet form is easier to use, with less odor. Not all chlorine is the same-- we'll explain the differences below.

Sodium Dichlor Granular Chlorine (granular spa shock)

Dichlor is the only packaged chlorine form suited for spas because although it is a little more expensive, it has near-neutral pH and does not require the addition of cyanuric acid stabilizer. It is primarily recommended as an occasional shock, since it is not available in tablet form, as bromine is.

It is neither excessively acid nor alkaline in character, and does not quickly deplete at higher water temperatures. If you use dichlor, the quick-dissolving fine granular formulation is the best.

Avoid the large pellets as they take too long to dissolve, and any particles resting on the spa bottom can cause finish damage. Since Dichlor is not made in tablet form, if you choose to use it as a sanitizer, more frequent doses and testing will be required than with time-released bromine tablets or some other sanitizer system.

It is best to dissolve dichlor in a bucket of clean water first, then add to spa water. (Pouring granules directly into a spa can sometimes cause acrylic surface discoloration from direct contact). Never mix different spa chemicals together; always add them one at a time.

A Better Way to Chlorinate Hot Tubs: Salt Systems

Saltron Mini is an easy to install plug-in system for hot tubs, which automatically produces pure chlorine from mineral salts.

Swimming pool owners have enjoyed the many benefits of saltwater purification systems for years. This revolutionary new chlorine generator makes salt technology practical for spas. Nexa Spa is an affordable plug in system which is simple to install, without any modifications to the spa itself.

Trichlor (pool tabs)

One form of chlorine, trichlor, is excellent for pool water treatment, and is usually supplied as tablets. We do not recommend this type of chlorine for spas because it has a higher acidic nature, and generally dissolves too slowly to be effective.

Prolonged contact with the spa shell can result in bleaching of the color and may even mark it, sometimes causing a permanent ring at the water line.

Cal-hypo (calcium hypochlorite)

This type of chlorine is popular for pool use because it's relatively cheap. It requires the addition of cyanuric acid to keep it stable in sunlight. Without stabilizer, it can lose 95% of its effectiveness in just a couple of hours.

Due to its high calcium component and high pH level, it tends to form deposits on spa heater parts and plumbing fittings, and may also leave an unattractive film or ring at the hot tub's water line. It is one of the most caustic forms of chlorine on the market, so avoid it in spas.

If you are going to use chlorine, sodium dichlor is well worth the few extra pennies in weekly cost.

Sodium Hypochlorite (household bleach)

Do yourself a favor, and keep household bleach away from your spa! Not only is bleach a poor sanitizer at higher water temperatures, it readily affects pH balance and tends to have a much harsher chlorine odor.

Avoid household bleach!

Household bleach can easily splash on surrounding surfaces, including your spa cover, and may cause permanent damage. Bleach also reduces filter life when used for cleaning.

Understanding Free, Combined, and Total Chlorine

Chlorine in spa & pool spa water may be present in two forms. First, Free Chlorine does the job of killing bacteria and oxidizing contaminants. When you add chlorine to the water, you are adding Free Chlorine.

When the Free Chlorine reacts with contaminants such as oils, bacteria and other organics, it becomes combined chlorine, or chloramines. Unlike combined bromine, combined chlorine has little sanitizing ability, and no oxidizing ability. Chloramines also have an irritating odor.

Combined chlorine, then, is like a spent bullet. Chloramines have a harsh odor, and can cause red eyes and irritation. (You'll have less chance of these problems if using bromine and can avoid them altogether with an  alternative sanitizer).

Combined Chlorine + Free Chlorine = Total Chlorine

Therefore, when total chlorine is higher than free chlorine, combined chlorine must be present. In that case you need to shock or superchlorinate your pool or spa.

Shocking with OxySpa non-chlorine MPS shock, or dichlor in an extra large dose will actually oxidize the combined chlorine and destroy the chloramines. You can test and measure Free and Total Chlorine with our Universal 7-in-1 Test Strips.

Dichlor Granular Chlorine

"Fast shipping, great deal, and it does dissolve very well just like you said."

Nancy Amond
Tallahassee, FL

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