So used to have a peacock eel when i kept FW Tanks. I have just recently ran across an engineer goby at my LFS for cheap. It seems as thouhg they are considered reef safe, and peaceful, however my only concern is the size. All my rockwork is fairly well secured (with only a few stacked pieces that are questionable). But my tank is only a 40gallon acrylic. How do you think a full grown engineer goby would do in this size of tank? In my opinion it is much better than the small 10 gallon the goby is currently in at my LFS.