Similarities

• Both UV clarifiers and UV sterilizers use ultraviolet light to kill algae and bacteria in the pond or aquarium in which they are used. The device attach to the pond or aquarium and emits the light over the surface of the water. The devices are designed so that they do no harm to beneficial bacteria that cling to rocks and live in the filter.
  
  

Differences

• UV sterilizers are stronger than UV clarifiers. They emit a stronger beam of ultraviolet light (UV-C light around 260 nanometers) that more effectively kills algae. Also, UV sterilizers are not submersible, whereas some models of UV clarifiers are.
  
  

Uses

• Generally, UV sterilizers and UV clarifiers serve the same purpose, and either can be used to clean the water of a residential pond. However, UV sterilizers are better-suited to use in areas where green algae thrive especially well, such as warm, sunny climates.