In my opinion a bog filter is the best biological filter that the average person can add to their pond to achieve crystal clear water and an easy to maintain pond. This video and the linked resources should help the average person build the right size bog filter for their particular pond.

For helpful products and articles visit https://ozponds.com

Here's a playlist showing some of the DIY bogs I've made    • Bog filter DIY videos  

And here's a link to a video on skimmers, intake bays and negative edges    • Pond skimmer vs intake bay vs negativ...  . It should give you a basic insight and probably contains links to some of these types of systems that I've built using cheap components.