The problem with the koralias (or Seios and MODDED maxijets for that matter) is that they are an AC propeller magnetic induction motor style pump... AC magnetic induction motors have the nasty habit of starting either clockwise or counter clockwise. This is a problem because a propeller style pump MUST spin in one direction only. To combat this, koralias and maximods use a mechanical stop on the propeller... So, when the pump comes on, IF it's spinning in the wrong direction, the propeller will literally collide with the mechanical stop and force it to go the other way. When you turn on one of these pumps, sometimes you will hear an audible click or thud as the propeller hits the stop and turns the propper direction. Longterm, using an on-off timer will destroy the propeller and the pump will stop working properly.
The solution with hydor koralias is to use the Seio pump controller. The seio controller modulates the AC frequency being supplied to pumps on the controller effectively throttling them up and down and pulsing the power to each pump. To the best of my knowledge, no other aquarium product does this for AC pumps. The Tunze pumps have a similar controller which ramps their pumps up and down, but they are DC powered pumps, thus you cannot mix and match controllers
Hope you follwed that rambling