Is filter pressurised or upflow. pressurised needs to be backwashed. air can be injected in up flow.

The problem with sand filters is they are not very good for pond water. Sand filters work well on pools because the water is already chemically cleaned.....no algae. The algae present in all ponds will quickly clog the sand. Bead filters are much better on garden ponds, but will still require frequent cleaning.

I'm thinking more and more bead filters are not very good either. I have 2 ponds with beads and 1 with a simple spraybar into a wet/dry filter media after a halfway decent prefilter and it never needs cleaning. The pre only needs flushing every few months. My bead filters need flushing a few times per week.

you are exactly right. Bead filters have a couple of advantages over an open gravity fed system (They are easier to plumb and they can go anywhere), but an open gravity fed system has many, many more advangates.

I've been looking up simple/natural pond filtering for a duck pond. It may not be possible due to the rather large amount of waste they produce, plus all the dirt and feed they carry in their beaks and spit into the pool.

But I did run across a really interesting design site that has instructions for a plant-based filtering system that looks really good for fish. It even makes sense. It takes a pump, but most of you pond guys already have pumps.

I'm still tempted to try it (or adapt it) for ducks. The water hyacinths he uses are pretty cheap if you can get them locally. Around here in W. WA they're $2.50 to $4. They seem to have attached "babies" that already have a good root system, so when you buy "one", it's really three or four, so you shouldn't need to buy too many. Some people say they multiply so fast you can almost just stare at them and see it.

Just FYI.

Sue

Here is a link that might be useful: Pond filtering with plants

I've used the Aquadyne 2.2 cf bead filter on my 4000 gal. koi pond for the past 8 years. Does a great job and cleaning is a breeze. I backwash & rinse about once a week....5 minutes is all it takes and my hands never get dirty! The Aquadyne filter coupled with a 57 w Aqua uv light and my pond water is crystal clear and the quality has never been better.