Have you changed anything about water flow in your tank just before the BTA started wandering? If so, this is why it's on the move. BTAs generally like low flow areas. I don't know how you're going to get it to stop roving, but I would suggest you protecting the intakes of your powerheads so the BTA doesn't get stuck in them. Contrary to the myth that BTAs "commit suicide" by deliberately getting stuck in a powerhead, they are roving to find a safe, low flow spot in the tank.
HTH
