Just as in human medicine, aquarium treatments for pathogens and pests often have undesired side effects or may even put the "patients" at risk. Antibiotics may inhibit the beneficial bacteria, so that ammonia or nitrite levels rise. Medications for "ich" and "velvet" often stain aquarium sealant, damage live plants, and stress the fish. Some stronger treatments for larger parasites appear to walk a fine line between eradicating the parasites and eradicating the fish. In "balanced" aquariums such as reef or heavily planted tanks, even the mildest treatments may tilt the scales enough to cause problems.

While chemical treatments are sometimes necessary, there is a technique for controlling many unwanted microorganisms with minimal disruption: Ultraviolet Sterilization.

Ultraviolet light incapacitates microorganisms by deactivating their DNA, making multiplication impossible or killing the organism outright. It does this without significant change to the water chemistry, and directly affects only organisms that are exposed to the UV (specifically UV-C) rays themselves, so it is a very safe and clean process, especially compared to medication. UV can be effective in controlling a wide variety of microorganisms, and has been used as a disinfecting process in other fields such as medicine, as well as tap water and wastewater treatment for decades.

The two main uses for Ultraviolet light in ornamental fish ...