I think I'm a bit confused. You have LR
on the bottom of your aquarium 4" deep? Sounds like gravel to me. Can you post a pic of your tank for us?
What Hara is talking about is, typically in a SW
tank be it a reef or a FOWLR
it has a sandy bottom like the ocean. Gravel is not a good substrate for a SW
tank. The sand provides a place for bacteria to grow and help with filtration. LR
is the large pieces of rock that are placed in the tank. If you have gravel on the bottom of your tank (stuff you see in a fresh water tank) then you really need to look in to getting that out and replacing it with sand. The BTA will typically attach its foot to a rock that is sheilded from the lights. Speaking of lighting what kind of lights do you have on your tank? The BTA is going to need pretty strong lighting to survive.