Alifer, I saw your tank and the question. All the answers are in this thread. Check the links it's all here..!
It looks like you're messing with your tank a lot and there is some kind of bucket underneath it. Koralia Nano for example has a magnetic attachment and will be fine on the side of your tank.
Also, instead of drilling the cylinder in the middle, I would go more to the side so you can position your rocks in the middle. In my opinion, for small tanks like we have it's nice to have a very clean look and hide all tubing as much as possible..