I plan on building a small waterfall in our front garden. By "small" I
mean very very tiny. The area I have to work with is about 5' by 5'. I'm
looking at a pump in the area of 100 gph. Pond size? Not sure yet. I'm
still doing research.

My question is what kind of filter is recommended for such a small size.
There will be no fish in the pond, the waterfall is mainly for
aesthetics at the front of the house. Every filter/skimmer I've
researched is huge (the smallest requires a minimum water flow of 400 gph!)

I just want water free of algae/bad smells/mosquitos. And I don't want
to change the water every two days. I'm really a beginner at this so any
help at all is extremely appreciated.

Thank You