There are devices that are considered essential for the support of a marine aquarium, such as a protein skimmer. In addition there are necessities that are housed by man and provided by Nature. The prime example of this is the bio-filter, where bacteria have their home in, say, a canister filter. Live rock of course is totally natural.
Then there are the devices that are not considered essential, but find favour with some aquarists but not with others. One of these is the UV filter. UV stands for ultra-violet, the light that is used. The UV filter is not an exclusive marine device, but also finds use in garden ponds. It is a normally fairly long and generally cylindrical device made of plastic with inlet and outlet at opposite ends. The plastic is the outer casing – inside is a glass envelope and inside this is the bulb. Between the glass and the bulb is a thin gap of about ¾” (circa 2cm) through which the seawater flows. Ordinary glass cannot be used as it absorbs the UV light, therefore it is quartz glass.
Seawater is pumped through the device and returned directly to the aquarium or sump. As the seawater flows passed the UV light, algae in the water column is damaged or destroyed (there isn’t any affect on attached algae of course). In addition, any parasites that are free swimming in the water column are killed or severely damaged so that they are no longer a threat. It is this latter action that is mostly of interest to marine aquarists.
If there is a cyclic disease in the aquarium UV radiation could be of considerable help. Diseases of this type have a stage where the parasites are free swimming when they are searching for a fish host. If these free swimming parasites pass by the UV light, as said they will be killed or damaged and no longer a problem.
This sounds like the absolute answer to the aquarist’s nightmare. Unfortunately, it is not. For the device to be totally effective it has to be guaranteed that every single free swimming parasite passes through the UV light. If this occurred the cycle would be stopped and the disease itself would go. Sadly, this cannot be guaranteed and it is likely that, subject to the severity of the disease outbreak, a few or many parasites would attach to fish thus permitting the cycle to continue. There are rocks and quiet corners in a display aquarium and sump and parasites might well escape seawater currents – even if they didn’t there isn’t any surety that they would be drawn into the UV filter intake.
So what use is the UV filter then? It is used as an aid to health in the battle against disease. I cannot give numbers or percentages for obvious reasons, but if some of the parasites are destroyed then the strength of the disease outbreak will be reduced, because there are that many fewer parasites to continue the cycle.
As said, some aquarists use them and some don’t. There isn’t any harm in using one and some aquarists run them continuously. If one is used it could be run continuously or for a period of several hours each day, the period controlled by an electric timer.
It is important to size the UV filter correctly, and the manufacturer will give guidelines as to what is required for any particular gallonage. It is also important to ensure the seawater flow through the unit is correct as to have an effect on parasites they must be exposed to the light for long enough. Finally, the aquarist must know when the effectiveness of the UV bulb is coming to an end and again the manufacturer will advise the expected bulb life. Here a notebook is useful as it is easy to work out how many hours a day, a week, a month etc the unit runs and therefore the period of time that will elapse before a replacement bulb is required. The aquarium cannot be over-irradiated, as the UV light is contained entirely within the unit.
The UV filter is an ally in the fight against disease and the treatment of it should it appear. It is not an answer to disease however. The major effort must be in the selection of healthy livestock and their quarantine before they are exposed to the livestock in the display aquarium, and the correct care of the aquarium to maintain a high quality environment.