check out this filter...
http://www.enkoi.com/filtration/ultima2.html

DD DDD wrote:

I have a 500 gallon preform. I want a external mechanical/biological
(maybe with UV) filter. Is there any really good ones? I have seen so
many types I dont know which to get. Also is the UV worth adding? And
also there is a pressure one with backflow.. I just want one that works
outside of pond and easy to maintain since I have a metal fence over the
pond. (need the filter outside. Size it not a problem.. If it cost
500.00 Fine... Im just tired of buying junk. I have 4 turtles 28 fish
and some frogs. So it needs to clean well... I have no plants, I may put
in a few but the turtles eat them and I want my turtles. LOL Thank you