You need to push down on the tube while you turn the tensioner with the hex key. The tube needs to slide over the long part of the hex key and needs to be just a few mm shorter in length. The timing chain tensioner is spring loaded and locks into a cam arrangement; you have to depress the spring with the tube to unlock and turn it with hex key. When you take it out you will see how it works.
If it is the the same as the EA to ED series engine, you also need a two pronged tool to unscrew the tensioner reatainer. If so you will find one of those cheap multifit disc brake piston adjuster cubes will fit the two holes like this works best and will allow you to retorque it to spec see http://www.autopart.com/Tools/file/part19.htm
They can be bought at Repco, Marlows, Rocco Bros etc etc. The special tool is essentially a long hex key with a screwdriver type handle and a stepped tube. Nothing too special. The T wrench type hex keys or any longer than normal hex key works best.,