Fluval Flex Aquarium Cooling Fan 40mm

After I bought a Fluval Flex 35l/9g (okay... just because it looked nice) I quickly noticed some flaws and / or opportunities to tinker :-)

So I started to redesign and add some things. This is Part 1 of the project.
Part 1.1 has a 80mm fan (https://www.thingiverse.com/thing:3671625)

The whole project will cover cooling, heating, light control, water refill (and whatever idea I will have in addition) using an ESP micro controller and without any destructive modifications at the tank hardw