A UV <u>DOES</u> work, but it doesn't FIX every issue known to reefkeeping!
It does what it is supposed to do, nothing more & nothing less.
Sterilization
In especially sensitive aquaria, infections resulting from water born
parasites, fungi, bacterium and vires can cause serious problems.
Water sterilization is most beneficial for breeders (as it can help
control infections of incubating eggs), for centralized multi-tank
filtration (to control the spread of disease between tanks), and for
delicate and/or costly setups such as large tanks and reef systems (as
a safety measure). It is important to remember that a healthy aquarium
depends on beneficial bacteria typically growing on media in your
filter which neutralize ammonia. At most, your sterilizer can kill
some water born pathogens, but total sterilization is not possible or
desirable. Aquarists who practice prudent quarantine procedures for
newly acquired fish generally do not need to sterilize.
Two main types of sterilization are used, ozone injection and
ultraviolet irradiation.:
Ultraviolet Sterilizers
High intensity ultraviolet light destroys the DNA in living cells and
can be an effective means to control living pathogens. The most
effective UV light is the high energy UV(C) light roughly at the
wavelength of 250 Angstroms. To be effective, UV Sterilization (UVS)
must expose the pathogens 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, which works out to
roughly 10 to 25 gallons per hour per watt (or less for units not
operating at peak efficiency).
Common problems which can reduce efficiency and kill rate are:
1. Allowing the water to flow too fast past the UV light.
2. Light blockage due to a build up of salt deposits or bacterial
slime on the bulb.
3. Fading of the light due to age of the bulb (which typically have a
six month life.)
The same property of this light that kills germs can damage your eyes,
and special care MUST BE TAKEN to avoid direct or indirect eye contact
with this light. [This is especially serious because the damage occurs
inside your eyes before you feel any pain. Too many people have
already damaged their eyes in this way!] The UV(C) light does not
penetrate water very well, so to be effective, UV Sterilizers commonly
position the UV bulb close to the water which also can pose a risk of
electrical shock should the bulb break, etc..
There are three types of UV Sterilizers:
1. Tray type. (Typically homemade) with UV bulbs suspended in a
reflecting fixture over a shallow tray of slow flowing water.
Benefits: easily cleaned, can be cheap, can be made large enough
for commercial applications. Problems: safety risks to your eyes,
too large and awkward for many home uses.
2. Tube type, wet bulb. Tube types have the benefit of exposing all
sides of the UV tube to water with no reflector. The water passes
directly past the bulb which is mounted in a waterproof tube.
Benefits: cheap, compact and effective. Problems: difficult to
clean the slime accumulations from the bulb, safety risks due to
electrical shock.
3. Tube type, dry bulb. Similar to above, but the UV tube is
surrounded by a quartz tube [glass blocks UV(C) light] insulating
it from the water. These are more expensive and probably safer.
Changing the light bulb is easier and dry bulb tube types can have
a internal device to wipe slime from the quartz tube. Some of
these types come with sensors to monitor the intensity of the
light to let you know when to replace/clean the bulb. etc..
