Those roots remind me of the Birds nests I saw in Namibia! The birds ( I can't recall their name this second) build massive colony nests with the openings on the under side! It is done that way to try to keep the snakes and critters from raiding the nest! VERY COOL PIC!!! I have some pics of the nests, and I will try to find them and post one here!
VERY COOL TANK 4SURE!!!
P.S. Julies are FREAKIN AWESOME FISH!!! I have had many types of them, and the ones you have chosen are VERY BEAUTIFUL and are soooooo fun to watch too!!! They will hover all around the rocks, and will also swim upside down following the underside of the rocks when searching for food to eat!!! You made a AWESOME CHOICE!!!