Inventor is way overboard to do an aquarium..... try Sketchup; it is easy on ones hardware if you don't have a xeon workstation with 32GB or more ram. It was aquired by Google 5 or so years ago and the basic version is free; great for novices and you can get better as time goes; you can get nice plugin and renderers to as well as limited file format import/exports. It is good for simpler squarish/architectural stuff - check it out.
Ample people from larger forums like reefcentral, nano-reef, reef sanctuary etc use it; they probable have the files / part files as well if you ask them or do a search on the freebie 3d repository at
https://3dwarehouse.sketchup.com/?redirect=1
regs
msjboy