Alright here are some photos of the desk.
On one photo you can see the overview which is similar to the way Linus did it.
On another you can see the tubing under the table. The loop order is (also similar)
res (1) -> pump -> pump -> rad -> rad -> cpu -> gpu -> res (2) -> res (1)
On the last photo you can see what I consider the problem: The pump isn´t sucking water, because it´s half filled with air! Even when I lift the reservoir 50 cm, the pump isn´t working properly! It is not running dry, but it isn´t pumping water.... I tried all ideas I got, do you have another idea?
Under both reservoirs theres a T -piece. The water flows through it, but if I have to drain the loop I can at least get the water out of the reservoirs..
It is connected via a quick coupling because I was a little bit worried when using a ball valve.