Be careful with black lights on your tank. Yeah it looks neat but black lights put out some pretty substantial uv a waves.
In nature, ultraviolet light waves (UV-A and UV-B) penetrate the ocean's surface but are filtered out as the light travels through the water. Both UV-A and UV-B light waves have been found to cause destruction of DNA and RNA within coral tissue. In response, many corals have made adaptations to reduce the effects of these harmful rays. These corals developed protective pigments that are often blue, purple, or pink in color. Most corals that contain these pigments come from shallow waters where the amount of UV-A and UV-B light is higher than in deeper areas of the reef