on the coralife pc
fixtures (well at least the 4x65 lunar aqualight that i own) the 10K bulbs are on the circuit that controls the cooling fans. the 10K bulbs put out more heat, so when they are on, the fan is also on. if ONLY the actinics are swtiched on, the fans do not turn on. if you switch the bulbs around, the actinics will be on the circuit with the fans, and the 10K's will be on the circuit without the fans. this means that if you turn on only the 10k's you may overheat your fixture. If you ALWAYS run your 10K and actinics at the same time, this really isnt an issue, but you really should keep the 10K bulbs associated with the circuit that controls the fans...
what you have to do is take the endcaps off the fixture, and change the locations of the bulb sockets... that way, the bulbs remain associated with the same circuits, and the fan will power on when the 10K bulbs are turned on.