Before you bother with the UV-sterilizer, you should just be aware of its limitations. Only what passes through it will be killed and in a reef with all of the live rock usually associated with one, a very significant proportion of any parasite infestation's spores will not pass through the sterilizer before they become free-swimming and reach a fish host. This would be the case regarding a FOWLR too. In addition, the "dwell time" regarding the "speed" through which the water passes through the sterilizer is critical in order to kill what, in fact, does go through it. So, you have to be certain to use a pump (and take into account the "head room" loss of the rate of the water-flow that the pump would push through it) that has a rate that is strictly in accordance with the manufacturer's recommendation. But, for effectiveness, the general rule is the slower the flow-rate the better to take advantage of the sterilizer's killing ability. On the other hand, UV-sterilizers are effective for keeping suspended algae under control and so for water clarity.
So...if you have it already and you don't mind springing for the new bulb, you may as well use it...but don't consider it a total protection from a parasite problem.