how big is it? how long have you had it? how big is the tank? when i got my bio-cube it came with two 6-inch engineers that the guy had moved out of his 120g. obviously they couldn't stay in the 29g so i traded them in when i broke the tank down when i bought it. anywho, i chilled and watched the 29 a bit before breaking it down and the engineers stayed hidden under the LR until he fed them at which time the darted around the tank eating up a storm. they were eating flake food. he said that was their typical behavior. so if you just got it maybe it's just getting used to the place. after i brought that bio-cube home it was about a month before the yellow watchman goby that came with it would come out at all - even to eat. i thought for sure the fish was going to die but now he's out all the time. hth.