As you may know there are many forms of chlorine that can be used to sanitize a pool. We shall list here the most common forms of chlorine and their pros and cons.
Dichloroisocyanuric Acid also known as DiChlor is a granular chlorine that can be used to shock a pool as it has a high concentration of chlorine within it. DiChlor also has CYA (Cyanuric acid) within it this helps protect the chlorine from the sun which can cause the chlorine within the water to deplete if not protected. Over time usage of this form of chlorine can cause for the CYA level to rise too high. Pros very high in chlorine good for shocking a pool. Cons are it can raise the CYA too quickly.
TriChlor is an extremely high concentration form of chlorine. If you use chlorine tablets in your pool these tablets are likely a form of TriChlor it also comes in granular form. This too can be used to shock a pool see below for more on shocking a pool. This too has CYA (Cyanuric acid) within it to help protect it from the sun. Pros are that in tablet form it’s slow dissolving and can hold a chlorine level within the pool for a longer period of time. Cons are it can raise the CYA too quickly and can cause issues on the pool surface if comes into direct contact with it.
Liquid chlorine. Comes in liquid form as opposed to granular easy to use and has a lower level of chlorine within it. Does not have CYA in it so it will not raise your CYA level. The water will need to have the correct amount of CYA within it to protect the liquid chlorine from burning off from the sun. Pros can be used to give a pool a chlorine wash if drained and algae is present. Cons can be depleted quickly if exposed to the sun with out the use of CYA.
The term, “Shocking” refers to the process of adding chlorine or non-chlorine chemicals to your pool in order to raise the “free chlorine” level to a point where contaminates such as algae, combined chlorine (also known as chloramines) and bacteria are destroyed.
Other forms not listed here are Calcium hypochlorite, chlorine gas and also salt pools. Salt pools generate chlorine themselves.
Here’s a video explaining the above as well.