What do cucumbers (holothurid?) eat exactly?
 

My reef inverts book says they need a deep sand bed, but do they just eat left over food and fish wastes or do they eat algaes (diatoms, etc) or?

I am looking to clean up my sand a bit - its constantly a brown tinge from the diatoms...

My black sea cucumber eats anything that is stuck to the sand.

THey feed on fish poo, detritus and bacterial films that develop on sand grains. Think of it like a house pet that eats anything you drop on the floor, but thats all it needs to survive.

Fred.

Sounds good so far - but does it feed on diatoms as well? How about other algaes?

If if grows as a biofilm on sand grains, and some diatoms do, then yes, it will be eaten by holothurids. Macro & hair algaes, no. They are not an algae control critter. If you are looking for a generalized algae eater, look for a diedema species urchin (see the latest Reefkeeping online issue)

Fred.