UV sterilisers used for marine aquariums.

The correct term for these is an ultraviolet germicidal irradiation device.
A UV steriliser doesn’t just kill, the light will eradiate and mutate the DNA preventing growth and especially the capacity to multiply.
All the parasitic and many other life forms that pass by this lighting live on for a while; it’s not a sudden death.
This type of lighting is normally a florescent tube utilising a short wave length consisting of intense ultraviolet radiation.Our atmospheric layers keep out most of the extremely harmful ones natural formed that these lights produce.
The sterilisers are used both for air and water circulating over or around them, for us it is only the aquariums waters that are passed around them. Microorganisms like protista, mould, viruses, pathogens etc that pass by this lighting are all irradiated.
This idea was original for medical sanitation, air purification and waster water, so these do come industrial strength sizes.
The idea is to have air or water pass over the sealed bulb or around the bulb if it is used with a quartz sleeve so the emitted radiation does it job at mutating the micro organisms DNA and eventually killing them.
For a marine aquarium there is no possibility that this steriliser can work on all microorganisms as they breed far quicker in the aquarium then can be passed over the bulb.
Then gap for the water to pass by the cover over the lights is extremely small to get the microorgamis very close to the radiation so it will eventualy kill them by it affects on their DNA with the cells of the creature.
Downsides to this form of filtration.
The bulb-tube cover has to be cleaned no less then each second day to keep irradiating at a maximum.
If life forms are potentially mutated and not killed, these can be undesirable to marine aquarium equilibrium.
Semi useless for fish only marine aquariums.
Harmful to reef aquarium stability, as it is disruptive to planktonic life that your corals depend on for foods.