This to a newcomer seems like a good idea, applying some extra protection equipment to the display aquarium and avoiding the need for a separate tank with the consequent need for extra heating, power heads and the like. Closer examination seems to be in order.
What is a quarantine tank? This is a smaller aquarium that is kept in addition to the display aquarium. Its purpose is to welcome new fish additions (and corals etc in many cases). The new arrivals are kept in quarantine for a minimum of two weeks, better four, so that any problems caused by the stress of transportation etc come to the surface and can be treated in isolation. If certain diseases raise their unwanted heads, then copper for example can be used, whereas in a reef aquarium it cannot as it is deadly to corals. In other words, newcomers are kept in isolation so that existing inhabitants of the display aquarium are not exposed to problems that could exist. Once the quarantine period is over and the aquarist is satisfied that all is well, the newcomers can be transferred to the display aquarium and the danger of problems is minimized.
The UV (ultraviolet) sterilizer is a piece of equipment that, as the name implies, helps to eradicate undesirable live content in the water – let’s just call the undesirables ‘nasties’. These could be bacteria or the spores of disease, mainly of the commonly called ‘white spot’ and ‘velvet’. What happens is that the water is pumped through the sterilizer, which is usually cylindrical. There is an outer wall and an inner one which contains the light, between is a thin gap. As the water moves through this gap life is exposed to the radiation and killed, or damaged to an extent that the ability to reproduce is severely impaired. It is very important that the water is pumped at the correct speed through the sterilizer so that there is sufficient exposure to the radiation, so the manufacturer’s recommendations need to be followed. It is also important that the given life of the UV bulb is not exceeded or the effectiveness of the unit will be reduced. Finally, the sterilizer should be sized to the gallonage it has to deal with.
So on the face of it the sterilizer could replace the quarantine tank (QT). It does exactly what is required, that is it destroys or damages unwanted nasties in the water. So there isn’t a need to keep fish in a QT as any nasties will be destroyed anyway. If only it was as simple as that, but it isn’t.
For the water to be pumped through the sterilizer there obviously has to be an intake. Logically the intake needs to be in an area where most water is likely to pass, so it needs to be where there is considerable circulation. So far, so good. Does this actually mean all nasties in the water will be sucked in and destroyed? Unfortunately it doesn’t.
In most modern aquaria, particularly reefs but also fish only, there is considerable decoration such as rocks or their substitues. This means that water will have quiet spots behind and under rocks or even just close to rocks. The method of reproduction of certain nasties is quite sneaky. They attach to fish where an aquarist can hopefully see them, then they drop off and go down into rocks etc. They then reproduce by division and where there were only a few there are soon many more. In the confines of an aquarium there can soon be high and increasing numbers. The point is that it is very likely that quite a lot of these nasties are going to be drawn into the steralizer, but not all. The ones left will reproduce and the problem can increase despite the presence of the sterilizer.
There has to be a QT then? The answer is yes, but there are considerable numbers of aquarists who seem to rely on luck and perhaps good judgement. The good judgement is choosing the source of their livestock and noting the condition of it, and the luck is that they were, well, lucky. By placing new fish straight into a display aquarium they are putting at risk the health of the livestock already there. Nowadays with better transport facilities and more knowledgeable dealers livestock should be in better condition, but there isn’t any guarantee of this, the danger of problems is ever present. There should be a period when a QT is put to use.
So the UV sterilizer is a waste of money then? No it isn’t, but it isn’t an essential either. The protein skimmer is viewed as an important assistant to the maintenance of high quality water. The sterilizer should be viewed in a similar way but with regard to health. The sterilizer is lower down the list of importance than a protein skimmer.
There isn’t any reason why a sterilizer shouldn’t be used if desired. It will help to destroy unwanted nasties and maintain health, or assist in the battle against existing disease. However, it is an aid to a healthy aquarium environment, not a guarantee of it.
If the aquarist maintains high quality water, provides a good diet and doesn’t overstock then there is a good chance of continuing good health. A UV sterilizer could be an aid but is not an essential as is for example a protein skimmer. If a QT is also used the potential for ongoing health is greatly enhanced.