was reading through your build thread, just thought id chime in here. I have 2 hass garden eels that are both well over a foot doing fine in about 4-6 inches of sand. they move often, from the shallower side to the deep side. they are perfectly fine in 4 inches of sand in my opinion. heck, they sometimes even move in the back where its 2 inches for a day or two. they just go horizontal once they reach the bottom. but i do agree with lbn that they should not go into a community reef. any big fish like tangs will scare them. they should be kept in a more peaceful tank with slower moving tank mates.