agreed with inthec,but i think you would need to cover it the first month of having the fish 24/7 and once its really happy and settled with its burrow, than switch to only nights. if you see it sleeps in its burrow, i dont think you would need a cover at all, but if u ever see him sleeping out of it, or is being stressed by something, get the cover back on. some pistols take a while to get a strong relationship with gobies, and every once in a while can kick them out of the burrow and even do that "clicking" thing at them wich freaks out the goby and causes him to make the jump. <- thats only normally when the goby is the near the same size as the pistol, if the goby is much bigger its normally the opposite