Is it a top pond falling into the bottom or just a waterfall/stream. (Maybe it's just my eyes can't tell from that angle) It looks nice though all planted up and with the bridge across. It would be good to see the whole thing from a distance I think.
Alison

Oops, actually that was the wrong pic. That's a close up of the filter and waterfall return. The filter is at the back, it's a 260 liter reservoir sitting in a lined "pit" with raised sides. The reservoir is partially sunk into the ground so I didn't need to make the sides of the pit too high, or use too much rockery to hide it. I wouldn't really call it a top pond, it's not that big... The "bridge" is just a home-made bench because there is no other way to access the filter and stuff without falling in - it goes right up to the hedge.

The white thing in the middle of the filter reservoir is a right-angle pipe joint where the water from th epump is directed to the bottom of the filter - where it then upflows through all the pan scrubbers and fake alphagrog layers. A black right angle joint would have been better, but I couldn't find one. Never mind - in the top of the reservoir watercress is growing nicely (to eat nutrients before they can feed algae in the pond) and should hide the joint it eventually. You can see an aluminium tube sticking out of the joint, which is my home made venturi to make sure the filter bacteria get plenty of oxygen.

The filtered water overflows the reservoir into the lined pit (which also has some barley straw decomposing nicely in it), then it flows into another reservoir with pickeral weed, golden sedge, marsh marigold and water forget-me-not growing in it... then it flows back into the pond via the shallow waterfall.

Lots of "dwell time" in each reservoir section, and the water doesn't flow that fast, so suspended material settles out quite nicely. I couldn't use a fast flowing or high waterfall, because the noise of it at night in Summer would be enough to annoy the neighbours trying to sleep with their windows open.

So far the filter has been working really well, the water is crystal clear, but the real test will be next Spring/Summer when the weather gets warm again and I'll see how well it controls algae blooms...

Hissy, are you going to use a UV?

Linda/Clive, no... I do have a UV unit that was in my OASE filter, but I was not happy with it. It seemed to kill algae at quite a rate, but the mechanical/biological filtration was insufficient, or the churn and flow rate of the pump was too high... so instead of green water I had a huge buildup of muck on the pond bottom and on all my plants etc, and water with a constant heavy suspension of dead algae. Water clarity remained terrible.

I'm going to see how my DIY filter performs without no UV, so far its fine, but the real test will be next Spring... I can always add it to the filter inlet if necessary, but I want to avoid it if possible and go with purely "natural" methods. Saves on electricity and replacement bulbs if nothing else.