84 in Manchester? Ah well, I wouldn't have thought it got that hot. How close are your t5's to the water? If it's like 1cm or so I'd raise it up several centimeters. Also, is it a closed canopy? Run a fan across the water or open up the lid before trying a chiller.
If you must, JBJ Arctica chillers seem to be good quality/value.
In summer I honestly just blast a few fans at the side and keep the lid popped, lol.
Display tank - 24g nano w/ softies/montipora
I run electrical appliances underwater and enjoy injecting things with Kalk filled syringes.