an object without any active buoyancy control will either float or sink. It will not remain suspended mid depth. In fact the feedback that does apply (compression) further promotes this behaviour. However ! a heavy object with only a fraction percent buoyancy . when subjected to heavy swell will spend most of its time completely submerged ! This because when submerged there is only a small force bringing it back to the surface, but once it breaks surface large forces accelerate it downwards again.