an engineer goby is very interesting to watch,it will redecorate your substrate constantly by taking mouthfuls and then spitting it out where ever it is building that day,I have one now going into its third year,its been in cc and a dsb which I think it prefers,but sifting the sand so often gets the tank a little cloudy once in a while,the juveniles look like coral catfish w/o the whiskers,the adults get a whole new look...and are supposed to be very hardy