When i go to the bathroom fire a bm it floats and this just started happening what could it be?

Most likely diet?: Increased air, fat and fiber can change the density of the stool. The more dense the stool, the less it floats. Think of it as a rock or a piece of foam rubber. Most likely reflects what you have recently eaten. If very foul smelling, mucous, blood, cramping, or other symptoms, get checked out. Mal-absorption, diabetes, infections and other things can be a problem. Doubt this is your problem.