Yea, it's like watching water boil or grass grow. If you ignore it long enough it will happen, if you watch it will seem to take forever.
IIRC, my percs sort of did that before moving into RBTA's, but they did it on and off for a while.
Try squirting some mysis into the BTA and see if the clowns follow it in. They might steal some of the food, but they might also suddenly feel right at home. (this is not an experience based suggestion, just a sudden thought, but maybe something to try?)