Adding a UV sterilizer to your aquarium is like insurance for your home or apartment. Proper use is reliant upon proper aquarium care, such as regular water changes and filter maintenance. UV only targets free-floating microorganisms, not nuisances attached to your fish, substrate, plants, decorations, or corals.

A UV sterilizer is used to control infections by stopping the spread of microorganisms from one fish/coral/invertebrate to another through the water. It is also used in pond applications to control free-floating algae. When operated correctly, free-floating microorganisms will be killed by the UV light.

Generally, the better, and most common, placement is right after the filter. In fact, a lot of the biological filters (that have a uv light built in) place this uv light after the filter itself. There are a couple of good reasons for this: … Having a filter before thelight prevents damage to the quartz sleeve.