Wet Chlorine, Dry Chlorine, and Concentrated Tabs. What’s the difference?

The good majority of all pools, in one way or another, use chlorine to prevent the buildup of algae and other contaminates. Chlorine can be added in the form of a liquid, dry powder, or tabs (salt – sodium chloride – is another method to generate this chemical using a salt system. That will be explained in a later post). A lot of people ask me when’s the best time to use each type, and well that’s largely dependent on the pool, environment conditions, other chemical levels, and personal preference. I find that in the hot summer months using all three forms provide the best results when I am only servicing the pool one time per week. The liquid chlorine gives the sudden boost to get the levels balanced, then the dry and tabs help provide the stabilizer and longer term chemicals to keep the levels from dropping before my next visit. For pools more susceptible to issues, I will generally leave a jug of liquid chlorine for my customers to add in the event of a hard rain or problem.

The best way to check the levels of your pool chlorine is by using a chlorine test. You can quickly do this at home by using the AquaCheck 7 Test Strips. I personally use these every day to check the chlorine levels of my customer’s pools because I believe they are accurate and user friendly. In addition, they show seven of the important chemical levels, including hardness, pH, and cyanuric acid, that impact pool cleanliness and health.

This post assumes familiarity with stabilizer (cyanuric acid). Refer to the post on stabilizer here for more information.

Liquid Chlorine:

This form of chlorine is what most people are familiar with. It comes in those 2.5 gallon yellow or orangewet chlorine jugs and is very obviously a bleaching agent. These are normally ~12% chlorine by volume with the rest of the volume being water and are about at 13 on the PH scale (that’s the top of the chart). 
Pros:

  • The benefit of liquid chlorine is it is burned up very cleanly in the pool and doesn’t leave any residue.
  • Most people can’t even notice when it’s been added to the pool since it’s added in at a liquid state and very quickly is diluted in the pool’s water.

Cons:

  • Liquid form contains no stabilizer (Cyanuric Acid). Stabilizer protects the free chlorine from being burned up naturally by the sun’s ultraviolet rays. Since liquid chlorine contains no stabilizer, it must be added in either manually, or from another source.
  • The liquid chlorine results in a sudden jump of chlorine in the pool. This level slowly dissipates as the days progress until either more is added or the amount in the pool is depleted.
  • High in PH, so acid must be added to manually decrease the PH of the pool if it becomes to high.

Dry (granular) Chlorine:

This type of chlorine comes in the form of a coarse powder. It’s often marketed as “pool shock”. It’s typically ~69% chlorine by volume. Using the dry form can be very beneficial as a supplement to wet chlorine in the hot months of the summer.
Pros:

  • Much more concentrated dose of chlorine than wet.
  • In the stabilized version, contains stabilizer (cyanuric acid), which helps protect the free chlorine from being consumed by the sun’s rays.

Cons:

  • It’s pretty expensive compared to liquid chlorine
  • Needs to be manually dissolved in the pool water. Many people think seeing it floating around is unsightly.
  • When the chlorine is burned off, it leaves behind a powder residue that the filter must pick up. This normally requires brushing the pool surface to remove it from the pool and get it in the filter.

Concentrated (tabs or pucks) Chlorine:

Another form of chlorine that most people may recognize as the hard white pucks in blue

chlorine tabs

floaters in the pool. These are about 90% chlorine and are the most concentrated. They act as a slow time release of the chemical and are packed with stabilizer to help maintain the chlorine from being burned off by the sun.

Pros:

  • Very low in PH
  • Slow release helps add chlorine through the week (see cons)
  • Releases some stabilizer into the pool. If the existing stabilizer is already low though, it may still need to be added manually. If the stabilizer is already high, this may create a problem (see cons)

Cons:

  • Contains a high amount of stabilizer which can cause problems if it’s too high. Refer to the article on stabilizer for more information.
  • Slow release is very slow. It’s not meant to provide chlorine when levels are already low. It should be used as a supplement when adding other forms of chlorine, but can be used to maintain already stable levels of chlorine.

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