UV Sterilization is the safest method of preventing and eliminating problems in an aquarium, or pond. UV will not kill a parasite on the fish, but parasites go through a free floating stage, at which point they are eliminated. Additionally, corals and fish can and do carry bacteria which can infect and spread throughout the tank, killing other inhabitants.
The initial thinking on reef tanks was to avoid UV, to keep plankton alive. However, with the skimmers and pumps used in ponds the plankton population in the water column is virtually non existent. You can use a UV continuously (recommended) or just keep one at the ready, in the event of an outbreak.