To kill Algae in your swimming pool you will need to add an Algaecide.  Long life algaecides are the perfect one off treatment, one dose is all that is required to see you through a swimming season.  Winterising algaecide can also be used to dose your pool over the winter to keep it free from algae.
Clarifiers are used to gather small particles in your swimming pool water together to coagulate them into bigger particles  so the filter can collect them.  Another way is by flocculation and the chemicals used are sometimes abbreviated to "floc".  Floc comes in either granules or as Floc tables.