I'm new here so excuse me for butting in...lol... We have an outdoor pond and always had problems with murky water..We bought a good bio filter and still had the same problem so I built a veggie filter and no more problem...Now my pond water is as clear (sometimes clearer) than tap water... I am building a larger pond and it will have a veggie filter for sure. IMHO, the bio filters are not worth the money...
My first veggie filter was made out of a cedar planter with a good liner covering the entire surface of the inside. I put lava rocks in the bottom and filled the rest with pea gravel.. My wife planted several plants in it and it works like a charm...