|Three different commercially available UV sterilisers.
L-R: Pondmaster 36W, Pentair Aquatics 40W, De Bary 55W
An ultra violet (UV) steriliser is chamber that exposes water to ultra violet radiation to kill free floating micro-organisms. A UV steriliser will not only kill bad things but will also kill plankton and beneficial organisms that also go through it. They are used primarily to kill bacteria, fungi, algae etc. and are extremely efficient, unless set up incorrectly.
How it Works
An UV steriliser works by emitting ultra violet radiation that mutates cells as they travel through the UV light and is lethal to living tissue Tank water is circulated through the unit where it is exposed to the UV radiation. If the amount of UV radiation and contact time are appropriate, everything within the water will be killed. However, if the water flowrate through the chamber is too high, there is insufficient time for the cells to receive a lethal dose of light. The water flowrate through the UV steriliser must be matched correctly with the UV tube to ensure appropriate irradition rates and contact times. This is first area where UV sterilisation is utilised incorrectly and fails to work as it should. If the unit is too small and/or the flow rate through it is too high, many organisms can pass through the unit unharmed.
Similarly, if there is no or insufficient mechanical filtration before the water passes over the UV tube, large particles can create shadows which decrease the efficiency of the steriliser.
The use of UV will not effect any other life within a marine system. This is due to the fact that is can only mutate living organisms that actually pass through the contact chamber, it does not effect the chemistry of the water (as ozone does) so the effects cannot be transferred back into the display tank.
Examples of Sterilizer
Do I need a UV Steriliser?
For the average, general reef aquarium hobbyist, no. It is far better to spend the funds on some other more key equipment for the system. They can be helpful with a large fish only type of tank or for use on a hospital tank to reduce parasite numbers. One issue with using on a reef tank is that it does kill anything that passes through the unit, including the "beneficial" plankton. They are not useless, need to set up and applied correctly, but for the average hobbyists, a UV steriliser is not required.
Will a UV steriliser kill ich?
UV sterilisers are not designed to kill complex organisms such as cryptocaryon (marine ich). Cryptocaryon and Amyloodinium don't spend enough time in the water column for the UV steriliser to be able to eliminate them. However, UV steriliser might reduce the number of parasites so they don't cause a problem but once its is turned off, parasites can reproduce again.