I set a tank up for my friend with a GalaxyPleco that was backlit with Blacklights 24/7. It measured 4' in length and then 10" X 10" He went with black sand substrate and peppered in a small bag of yellow and green flourecent gravel that reacted under the BL and then he backlit the thing with a black light.
It looked cool and the Pleco prospered. They make plants that glow under a blacklight too.