I saw one of those moving bed filters and thought they were pretty cool to watch. I ordered some K1 media, which I still have plenty of, and gave it a shot. I watched so many videos from King of DIY and Aquarium COOP.
The first attempt was in a small 12oz. water bottle for my 5 gallon guppy tank. Then I went to Quicktrip and got a liter bottle of Mountain Dew so the bottle would be green. You can see that filter I still use in my 20g big tank.
For my next project, I am looking at a DIY cannister filters. What are some of the things you've DIY?