Fun fact about myself: I build aquariums for a living. 
Is that hard?
Well, the concept is simple-plants, water, and a container, but larger ones can be difficult
What is that thing aquariums have that filters out the bad bacteria and germs? The motor thing from Finding Nemo.
I like to build my aquariums without a filter, but rather, I like to place enough plants in the aquariuam so they produce enough oxygen to sustain the tiny ecosystem.