I have a green carpet, about 8"across. I also have a RBTA. The RBTA has stayed at the top of my tank. I put the carpet on the bottom of the tank where I wanted him, and he DID move about 6" away from where I had put him. All is fine though. I did loose 2 different orange diamond goby's though. Couldn't fine a body or a trace of them, then I thought about the carpet. No mandarins in my future...