I like your filter design.. I plan on making a down sized version of this for my tiny 20 gallon water garden which is now home to 2 small Koi, until winter. I have a plastic 1 gallon jug which previously held candy. It's perfect for this because I can easily add an input and output and a small drain to the bottom. My only question is since it's clear should I paint it dark to prevent algae from forming inside it, also how is the good bacteria affected by sunlight?
Thanks for the idea..