Thanks for the quick reply but I went to bed.
I also thought it could be turning into vapour as there are droplets on the side of the swiftech micro res above the fluid level but this can not escape the loop as the res has a screw down top with 'o' ring. As for air in the loop I can not see any but the radiator is the highest point so it is possible for air to be making its way out. The thing is my system is on 24/7 and has now been water cooled for the last 4-5 months. So would there still be air in the system?