I don't know yet how i want to make the filter cause there are several options.
On the pictures you can see an example of how i could make it.
The filter excists of a relatively small before filter and a room for the pump, than the water will be spraid into the dry filter. The whole dry
filter is filled with bio balls and substrate.
I could of course also choose for a somewhat more confessional preparation with for example a large wet biologist.
Feel free to give your opinion ...