New guy here but trust me do not attempt to move and just let it move where it wants to. Mine keep moving to the back of the display so, I would spin the rock around so he was at the front. Or I tried moving by putting a powerhead blowing at him until he released. Each time, he would move someplace else. Like you I have a 55 and running koralia's. Long story short; Koralia 1 BTA 0 about 2 weeks ago the BTA floated up into the powerhead and the rest is history. Next one I get will be placed where I want to it to settle but, if and when it moves then that is the way it goes.