What Pool Chlorine Type is Best for your Pool?
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How to buy the right type of pool chlorine

First, let me put two misconceptions to rest. Chlorine for above ground pools is the same as chlorine for in ground pools and there is no one best chlorine for a particular pool type.

There are two simple questions that can help you determine what type of chlorine is best for you. Some of the choice comes down to preference. Starting out though, let’s get to the basics of what chlorine types are available.

Chlorine can be either Stabilized or Unstabilized. When many pool owners hear that their chlorine is unstabilized it conjures up images of beakers exploding in laboratories. With chlorine however, this refers to the addition of a chemical called cyanuric acid to the chlorine. CYA shields the Cl2 molecule from the sun, sort of like sunscreen for your chlorine.

So the first question should be, “Is your pool indoors or outdoors?” Indoor pools don’t really need stabilized chlorine, and neither do portable spas. For this reason, and the greater stability at fluctuating pH levels, these types may find benefit in using bromine, a close cousin to chlorine.

Liquid Pool Chlorine or pool bleach, sodium hypochlorite pool chlorine types, pool chlorine tablets or trichlor tabs pool chlorine shock, dichlor or cal hypo granular pool chlorine


Types of Stabilized Pool Chlorine

1” tablets, 3” tablets and sticks are the EXACT same chemical compound (Trichloro-S-Triazinetrione). So whether you call it a tablet, a puck, or a stick you are getting the exact same product. If you have an outdoor pool you need the stabilized chlorine and per pound the three inch chlorine tablets are the cheapest. Additionally, if you are using a chlorine feeder most are designed for the three inch chlorine tablets. So to get the most chlorine in your feeder at one time use the three inch tablets.

Why would you use the 1 inch tablets or chlorine sticks? This comes down to surface area; when you place the one inch tablets or sticks in your feeder they don’t line up as smoothly as the three inch tablets do. What this does is gives more surface area for water to erode the tablets – thus increasing the chlorine level more quickly. Another use for 1″ tablets is for chlorinating spas or very small pools, in which case a 3 inch chlorine tablet may be too large.

The other form of stabilized chlorine is a certain type of granular pool shock. While granular still has the stabilizer in the chemical compound (SodiumDichloro-S-Triazinetrione) the difference comes in the percentage of available chlorine and the effect of granular chlorine on the pool water. Stabilized chlorine shock or granular should have 56% available chlorine. What it lacks in potency it makes up with by having virtually no effect on your pool water pH level.

Types of Non-Stabilized Pool Chlorine

Liquid chlorine (sodium hypochlorite) – popular in many parts of the country, has some complications in its use.
  1. It is only 10-15% available chlorine, and has more sodium than chlorine.
  2. It is the fastest acting due to the fact that it is pre-dissolved.
  3. It is un-stabilized or unprotected against the sun’s UV rays.
  4. It requires a specialized feeder or the pool owner to pour it into the pool.
    1. Pouring it directly into the pool will cause the chlorine to have peaks and valleys instead of having a steady safe level.
    2. Increases pH Levels dramatically, with a pH level of nearly 13.
Pool shock can also come in other granular forms that are not stabilized, such as calcium hypochlorite. Cal Hypo, as it’s called, has a higher level of available chlorine, at 65% – but is not stabilized, or protected from the sun. A real Grade-A Fancy pool shock, lithium hypochlorite – is only 35% available, but is fast dissolving, suitable for vinyl liner pools, but also non-stabilized. Non chlorine shock, usually potassium monopersulfate, is also unstabilized, because it’s, well…non-chlorine.
All pool shock granular products should be used for superchlorination, and not as an every day chlorinating method. The burn rate is very fast, and like eating Chinese food – your pool is soon hungry for more.

One thing that all chlorine types have in common is that when they dissolve in water, they produce hypochlorous acid, which is the active ingredient in chlorine. Without it, contaminants, organic matter, viruses and pathogens begin to grow in any untreated body of water.

I’d be remiss if I failed to pass along a bit of safety information about pool chlorine:
  1. Never mix different chlorine types together. They will react violently.
  2. Follow all label instructions when transporting, storing and using chlorine.
  3. Never allow dirt or any foreign substance or debris to contact chlorine.
  4. Keep chlorine tablets and granular in a cool, dry location, away from children.
  5. Never allow any other pool chemical to come in contact with chlorine.

So, in answer to the question: “What type of chlorine is right for me?”, consider your pool size and location. Outside of that I like to tell people, Buy the best chlorine at the lowest price, look for a low cost stick or tablet, from a company you like, and you’ll be fine.

Enjoy your Pool!


Brett Rotelli
IntheSwim Staff Blogger


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