Hey Mate, the red nulon coolant that you got is correct, as previously mentioned, NEVER mix coolant types unless you want throw money away, and if its down only a little bit, just top up with demineralised water (you can get it from supermarkets for a couple of dollars)
But! if its down a lot or its been going down over a few weeks, check for leaks around hoses and the water pump... If yours has done over 140000km then check the water pump... (they usually need replacing around the 140000 - 160000 mark) i know, i just replaced mine!
Oh, and go to Repco, at least they know what they are talking about...