What exactly is UV sterilization? It's actually a very simple process for removing (referred to as filtering) unwanted free floating microscopic water borne bacteria, parasitic, fungal, viral, algae, and other unfriendly pathogens out of aquarium water by exposing it to high intensity ultra-violet (UV) light. UV light has the ability to effect the function of living cells by altering the structure of the cells nuclear material, or DNA. The end result is the organisms die off, eradicating your aquarium water of these unwanted nuisances.
But, in addition to killing beasties, UV sterilizers also, well,
sterilize the water. They do this by producing ozone if they
receive oxygen-rich water. The ozone is produced in much smaller
amounts than that produced by an Ozone generator, but it is enough
to clean the water and increase Redox potential. This process is
very similar to that keeps an Ozone layer over the earth. UV light
strikes Oxygen molecules and Ozone, O3, is produced, which is highly
reactive. This Ozone can then bond with pollutants and neutralize
them (much simplification done here). As for the Ozone over the earth,
the same amount is being produced all the time, it's just the Chlorine
now exists in the layer in the form of CFC's, and much of the Ozone
bonds quickly with the CFC's instead of other pollutants, thus
sort of depleting the layer, but it is much more complex.
Granted, a sterilizer is not an essential part of equipment -- if you
exercise good quarantine practice before introducing livestock (including
live rock!), you really don't need it. It's just a handy thing to have as
a back up against ick (in case there would ever be a temperature shift or
some other catastrophe).
The general consensus is that an aquarist that has a well maintained and uncrowded aquarium, as well as follows good quarantine procedures when introducing new specimens to their system, a UV light filter is not necessary. For those that may be deciding on whether a UV light filter should be added or not, here are some other points to consider.
Most effective when run 24/7.
Most effective if the water is clear.
Most effective if bulb is new, or replaced regularly (at least every 6-8 months).
Most effective if the UV light penetrates less than one inch of water.
Effectiveness can be hindered if the water passes to fast past the bulb. Most effective if the exposure time of the water to the UV light is longer than one second.
The effectiveness of UV light can be hindered if there is light blockage, i.e. a salt encrusted bulb.
It can help to prevent future water borne pathogen reoccurrences, once the initial problem as been completely eradicated from the aquarium.
UV light not only kills unwanted organisms, but beneficial ones as well.
Because it can destroy beneficial microscopic organisms that some reef tank inhabitants may depend on as a food source, UV light should not be run during feeding time.
It only destroys organisms that are free floating IN the water as it passed by the UV light, i.e. it will NOT get rid of an ich infestation that is already ON fish, or cure a bacterial disease fish may have.
Should never be run when treating with any drugs or medications.
UV can also alter the structure of some dissolved chemical compounds.
UV light can be damaging to the human eye, so DO NOT look into the bulb.
Always unplug the unit when working on it to prevent possible shock if it breaks or gets wet.
UV can also alter the structure of some dissolved chemical compounds, so you do not want to run your UV light filter when treating your aquarium with any drug or chemical medication. Because many of the inhabitants of a reef system are dependent on good types of micro-organisms for food sources, you may not want to run a UV filter in this type of aquarium.
To be effective, UV Sterilization (UVS) must expose the germs to high enough
light intensity for a long enough period of time. Martin Moe cites 35,000
to 100,000 microwatts per second per square centimeter as the norm. The
most effective UV light is the high energy UV(C) light roughly at the
wavelength of 250 Angstrom.
