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Chlorine: the 3 Common Types and When to Use Them

Updated: May 6

When most people think of pool chlorine, they think of the big 3" tabs

chlorine pucks
3" Chlorine Tabs

. Indeed, it is the most commonly used and most popular chlorine item out there. They come in 1" and 3" versions. Some even have algaecides, clarifiers, and chlorine boosters in them as an "All in One Tab" for easy, year long pool treatment - cutting back on buying algaecides and clarifiers. However, this is just 1 of the 3 common types of chlorine for pools and when to use them.

I'm going to tell you about 2 other versions of chlorine besides the stabilized3" tabs that are just as effective, (if not more effective in some cases) as well as when and how to use them. These products can all be found on our online store and are readily available to you.

liquid pool shock
12.5% Liquid Chlolrine

The first option to 1" or 3" pucks are liquid chlorine or liquid pool shock. It is simply a chlorine that is not pressed into pucks, but rather in a liquid form that you can simply pour into the pool. It is a simple way to quickly add chlorine for immediate swim time. You can add as much or as little as you like depending on your chlorine levels. The technical term is sodium hypochlorite. It comes in the strongest strength of 12.5% or a much weaker strength of 10%. Although this may not sound like a big difference, the fact is you will need 1.5 to 2 gallons of the 10% to equal the strength of a 12.5% version. Pool contractors, swim facilities, and pressure washing contractors will always choose the 12.5% version due to overall cost and time effectiveness. Accordingly, pool stores will only carry the 12.5% version.


- liquid chlorine does not need to slowly dissolve like the 1" or 3" tabs, it provides an immediate chlorine reading.

- it can also be used as a shock for once a week treatment and does not leave any granules or white powder behind.

- if you have combined chlorine, this is an excellent option to break it.

- if you have a cartridge pool, this is the way you want to go. It leaves no powder or residue that can gum-up your cartridge.


- It does not have any stabilizer in it. What this means is you need to have already put chlorine stabilizer in the pool for this to work effectively. Chlorine is naturally a gas, so it wants to "gas off" and return into the air. Stabilizer dramatically slows down this process to keep the chlorine in your pool so it can sanitize. With liquid chlorine, the stabilizer already needs to be in the pool, (which is no big deal, you'll need to have a good stabilizer level anyway if you want to keep a chlorine reading). 1" or 3" tabs already have some stabilizer in them, but you will initially need to get your pool's stabilizer reading up anyway. Tabs just help replenish these levels after backwashing). If you do not have a good stabilizer reading, the liquid chlorine will gas-off overnight, so be sure to have a good amount of stabilizer in your pool BEFORE you use liquid chlorine. I recommend a 40 to 60ppm of stabilizer.

- You need to check your levels a couple times a week. Since the liquid chlorine doesn't slowly dissolve over time like tabs do, you want to make sure your chlorine readings remain in a good range. (It's not that big of a deal, you just need to check it a little more often)

- It takes up more storage space. Since liquid chlorine comes in Gallons, you need to allot more space to store it. Keep it out of the sunlight when storing.

#2 Chlorine Granules

chlorine granules for spas and pools
Chlorinating Granules

The 2nd type of variation to tabs is to use chlorine granules. You may think "OH, this is just crushed up tabs"... It's not. Chlorine granules have a different chemical makeup than tabs. They are a Dichlor. Tabs are a Trichlor. As I said earlier, tabs have some stabilizer in them, chlorine granules do not.


- chlorine granules dissolve much quicker than tabs and are better for cartridges.

- Chlorine granules can be used to successfully kill and prevent mustard and black algae when used with a strong algaecide. Under normal circumstances, regular tabs and shock will rarely kill mustard or black algae, as these types of algae's grow immune to the normal pool treatment of shock and tabs. Hitting it with chlorine granules (or dichlor) introduces a different form of chlorine that they're not used to, which kills the algae and helps to alleviate future problems. (It is how I kill those types of algae.)

- They are great for hot tubs. Since hot tubs use cartridges, it keeps the cartridges from getting the gummy debris that tabs leave behind. It also has no stabilizer in it, so your hot tub doesn't get overloaded with stabilizer as time goes on.


- it is more expensive than chlorine tabs.

- since there is no stabilizer in them, you have to get your stabilizer reading in the appropriate range before they will work. (Like I said earlier, this is no big deal because ALL chlorine or salt pools need to have a stabilizer reading in them anyway.)

- since it is more expensive, it may be harder to find than regular tabs.

Here is an easy way to determine which ones to use:

*If its a sand filter pool: use tabs and shock or liquid chlorine.

*If it's a cartridge pool, use liquid chlorine as both chlorine and shock.

*If you have mustard algae or black algae, use chlorine granules in conjunction with a strong algaecide such as Algatec.

*for hot tubs, use chlorine granules.

It is also a good idea, no matter what type of filter you have, to treat your pool at least once a month with chlorine granules in the heat of the summer to prevent the growth of mustard algae or black algae. After all, an ounce of prevention is worth a pound of cure!

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