This is a fairly easy to build and inexpensive waterfall / pond filter that will out perform those costing hundreds of dollars. I had spent a lot of time trying to find a way to keep our small Koi pond clean, we had tried several different fountain / filter set-ups but the filters would need to be cleaned every couple of days and if it was windy the water would get blown out of the pond, it doesn't take long for a 120 gallon pond to get real low on water. I came up with the waterfall after a lot of trial and error but it was definitely worth it, the water stays crystal clear, the fish grow great and stay healthy, the water plants thrive (both in the reservoir and pond) and best of all you don't have to clean a filter almost all summer long, when you do the initial spring set-up for about 2 weeks after you have to clean the filter and pump a few times but once things stabilize you can just sit back and enjoy.
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https://www.youtube.com/watch?v=HqdryW2Meg8