A steriliser will be useful in two ways: as a clarifier and for microorganisms. As a clarifier, it will improve the visual appearance of what you see in the aquarium while working on algae and greenwater. Microorganisms such as bacteria, viruses, and protozoa are typically not visible and assist to prevent these organisms from being transported from your aquarium residents such as fish, invertebrates, and corals to each other and free floating in your aquarium.

How effective is a UV Steriliser?

There are several elements that must be considered in order for a steriliser to function properly:

It must float freely in the water column.

It must go through the UV Steriliser.

The UV must be powerful enough to destroy viruses, algae, bacteria, and protozoa.

There must be enough dwell time for the organism to come into touch with the UV.

While a rock in your aquarium with algae on it will not be impacted by the UV because it is not going through the UV, spores floating about in your water will be affected since they, like virus, bacteria, and protozoa, can travel through the UV.

The greater the wattage of a steriliser, the more light it can create, but bear in mind that the bulb has a life and has a life span between 6-12 months, and as it gets closer to the end of its life, the emission will also be decreased, and frequent maintenance is essential for optimal use.

Dwell time, or the amount of time that the organism is exposed to UV light, is also an essential component. This is a mix of the length of the UV that it must travel through, to which the organism is exposed, and the duration; if the flow of the unit is too quick, the steriliser will be useless.

A Eheim Reeflex 11 watt UV Steriliser, for example, may have a maximum flow rate of 1200 litres per hour as a clarifier and having clean water but it would not provide adequate dwell time to help with microorganisms – the flow would need to be a maximum of 600lph to be effective on microbes.