Making the assumption the Biocube is the compact flourescent version (?), they tend to run warm. when the lights are on. Several of us have the same problem
but a few ideas.
1. Buy some of those refreezable gel ice packs..like you would use in a cooler for camping. I put one of these is a ziplock bag and then suspend it in the waterflow..it'll take te temp down a couple of degrees before it compeltely defreezes. I use this as an emergency measure..normally during hotter weather.
2. I elevated the main canopy with a dowel cut to the width of the tank. I used netting material, like from a pool hand skimmer, and attached it to the canopy (top and bottom) in order to keep my Firefish where he belongs. With this, I aimed a small desk fan at the top of the tank to help blow out the warmer air..this kept and keeps my temps at about 75...also add in the general cooling feature of a ceiling fan.
3. Purchase stronger fans and replace the ones in the canopy. I can't say what the standard size was as I upgraded my lighting and new fans came with the kit but mine uses a standard 50mm fan. You'd have to check your fan size to verify but they are easy enough to get to once you unscrew the plastic light guard. Fans in general are very easy to replace.