Smitty is right. although they are small, they still have a good current flow. by getting 2 and placing them on opposite sides you can have an alternating current so it gives it the natural current flow that fish and coral like and i dont know but maybe u can stick the Koralia somewhere near the back so that you live rock get some what of a current behind them.
A friend of mine has his tank with a MP40 and a Koralia 240 and he told me that getting that MP40 was the best thing his done and highly advice me to get one but i dont have that kind of money.
Im new to this but ive been doing nothing but research for the past 3 weeks lol.
I have a single MP40 in my 180 right now (couldnt afford two at once) and I would agree that its the best powerhead I've used (I've tried several different brands of powerheads) the amount of water this thing moves is incredible - and it does it without putting the sand in suspension. Other powerheads were moving less water, but whipping the sand up more because of the tight stream of the flow - versus the wide flow of the vortech