This post is a bit more technical. It gives insight into the setup of the filter system + pump.
It also shows the materials that I used to cover the back and the bottom of the tank.
In this image you can see the two inflows: one is used for fresh water, and the other one is the outflow of the filtration system:
This picture shows the other side, from the filtration compartiment. The right connector is a so called GARDENA connector.
This picture shows the filtration inflow, and the Trespa plate I use to protect the bottom of the tank:
In this image you can see the filtration area filled with blue material:
I changed one of the three blue elements every month. You just pull it out, put it in a bucket, clean it in the shower, and then put it back in.
In the last compartment I had an OceanRunner 3500 (900 gph), which had enough power for this tank. More on this pump here. I can really recommend this pump for INTERNAL/SUBMERGED use. For external use I recommend an Eheim with similar power, as they tend to leak a lot less.
In the filtration department I also had two electric heaters of 300 Watts. Two, because one was the back up for the other: I simply put its temperature limit 2 degrees lower then the other one.