I have noticed that UV sterilization is often a subject of wonder or uncertainty. I personally have one unit on my largest of four tanks.
What is a UV Sterilizer?
It is a process using ultra violet (UV) light for capturing and making sterile unwanted free-floating bacteria, parasitic organisms, algae and marine ich protozoa. The light in the UV attack the living cells by altering the structure of the cell's nuclear material. This causes the organism to fail to reproduce, eradicating your aquarium of all associated nuisances and blooms.
UV sterilization is accomplished by running water in and out of a chamber that contains a UV sterilizer bulb which is housed in a (quartz) glass sleeve that is in the shape of a tube like bulb.
Setting the unit up:
The 3 types of UV sterilizer units are in-line tank (water flows in and out of unit and marked on the housing as such) , hang-on version and pond version. Most units are designed to be hung vertically. The in-line units mount underneath the tank (mine is next to sump) using an external pump or routed from a return pump to the tank.
The hang-on version hangs the unit on the back of an aquarium. This type is easiest to set-up, but it is highly visible outside the stand and considered unsightly to some. This is why I chose the sump as my location.
It is important that the pump used has an adequate flow rate to allow water to pass through the unit. It is also important that the pump has a flow rate within the safe flow range of the uv sterilizer. The acceptable flow rates are determined by wattage, gph (gallons per hour of flow needed to sterilize bacteria or clarify the water of algae) and method of flow (hanging or sideways mount.) Obviously the faster water travels through unit, the less effective the unit will be. Too slow is not good either as sediment will be allow to stick to quartz sleeve. A moderate/steady slow is favorable.
What can be expected when using a UV unit:
UV sterilizers do what their name suggests; they sterilize free-floating algae which has to travel through the sterilizer to be sterilized. If the microorganisms can't be sent through the UV unit, they will not get sterilized. Additionally, they will treat and eliminate protozoan parasites such as ich during the newborn, free-swimming life cycle and adult stage of the parasite. Just like algae, parasites have to pass through the unit to be affected by UV. If the inhabitants have the disease already, unit will have no effect as the fish cannot swim through the unit.
Things to keep in mind when using a UV unit?
UV lighting can affect some dissolved chemical compounds in the aquarium and should be used with caution when medicating. It's also advised to turn off protein skimmers while using it. In general, it's better to turn the UV unit off when applying medications and other treatments.
One other point is to consider is using a timer which will turn the UV unit on in the morning and off in the early evening (you can use this same schedule with your lights) as many free-floating beneficial foods like phytoplankton emerge in the tank when the tank becomes dark and can be killed by a UV sterilizer.
Maintaining the sterilizer unit:
UV bulbs should be replaced annually or sooner if you're using a lower wattage type. Just like your tank lights, UV lamps will lose their intensity and effectiveness and become ineffective as the bulb ages. If your tank has lots of suspended matter, or detritus, you may need to clean the quartz sleeve that surrounds the UV bulb monthly to bi-monthly as the light needs to penetrate the sleeve to come into contact with the water that passes through it. Cleaning can be accomplished by using either alcohol or a vinegar/water mix.
Are UV sterilizers safe?
UV sterilizer lights as with any bright lights can damage the human eye so avoid staring at the bulb. Always remove unit from the mounting location and unplug them when working on them.
The 3 types mentioned:
hang on type: