A screen medium of a mobile multi-deck screen is tensioned with a tensioner. A tensioning link engages and tensions a screen medium on a side thereof by at least two linear tension rods, when the screen medium side tensioner is installed to the mobile multi-deck screening device. An adjusting member causes for each of the at least two linear tension rods, a linear movement tensioning by the tensioning link the side of the screen medium above the two linear tension rods. A retractor disengages the tensioning link responsively to untightening the at least two tensioning rods. A screen deck, a screen and a mobile multi-deck screening device are also disclosed as well as a method for replacing a screen medium using the tensioner.