I thought Id leave this here.
My house had a large (~50K liter) old and neglected pond, that looked like this:
Its rather nice, but the water was clear as mud. There were supposedly some fish in there, but you wouldnt be able to spot the Lochness monster
I decided to clean it up last year. A hellish work I tell you.
And to prevent it from becoming a mud pond again, I wanted some filters. Pond filters for a pond this size are exuberantly expensive, think more expensive than a small car, so I built a cheap DIY bio filter from plain rain barrels and some plumbing material.
Not exactly pretty, but I hid it well out of sight.
I didnt expect it to turn the pond in to a crystal clear aquarium, the pond is surrounded by trees, and really, from everything I read, I would need at least 3-4x more barrels for a pond this size. I would have been content just being able to spot my fish, but the results surpassed my expectations.
This is the result one year later, pics taken this morning; granted, its not an aquarium, I have certainly seen more clear water, and the water has a green/yellow tan, but boy am I happy with it!