A bio-filter never hurts. When rebuilding my pond of 20 years, 5 years ago, I used the Alpha One 2.5 >>>
If someone has unlimited funds for their pond, check out some of the assembled units on the platforms.
Amazing along with amazing prices. They're complete systems with UV's to boot. I bought my
components separately and created my own setup....
http://www.aquabead.com/AquaBead-250-Filter/AquaBead-250-Filter-from-GCTek-p-28.html ...
It's costly and the picture is without the external pump. It's low energy at 1/4 horsepower. Check the
site out. Some outrageous things. The owner was quite good when it came to warranty. I had only one
problem with the 1 hp bead blower as I left it on from March to November. The inside from humidity became
rusted. I rebuilt it, but, he sent me a brand new one at no charge and suggested popping it when not in use.
I also put a Jandy valve just under as a failsafe in the event the spring valve went. Other than that, I swear by
the unit. Never have ammonia or nitrite problems except when 3 koi spawned at once. Ugh! Wish there was a way
to sterilize female fish. What a mess. 2 spawned within a day of each other, cleaned up the mess and the 3rd female
2 days after. Bizarre! Took a toll on the pond and me ... lol ...