Cucumbers are notorious for cleaning the sand bed of coral reefs and rock reefs eating detritus.  They move along aerating the sand and release debris and pollutants that have been trapped, making them an essential invertebrate in all environments.  Cucumbers do not tolerate high nitrates and will live a long healthy life with stable conditions in a well established environment.  Cucumbers are peaceful but also carry a toxin for protection from predators.  They may need a supplemented diet of meaty seafoods, flakes, and pellets.