while this statement can ring true in some circumstances.... I NEED a filter and NEED a UV, my pond is in full sun for 10+ hours a day.... it will house alot of Koi that will be feed heavily, and Iwant enough open water to actually see my koi......

be careful what you recommend....

some folks have ponds with fish and they dont feed their fish, where as I go through large amounts of food and my koi grow like weeds

this is true in the specialized case you presented, but what happens if every part of the yard has full sun for at least 8 hours a day? what happens if the koi eat the plants? I do totally agree with the 4 foot deep part but that alone won't stop herons as my buddy found out. you need to have a shelf they can go under also, but you have to make sure it isn't shallow enough to allow the herons to stand on it :rolleyes:

anyways saying you do not need them should have been tempered by if you have perfect conditions which 90% of us won't.

Steve

I have never had perfect conditions and I have never had a UV, filter or other stuff and I overfeed the koi.

If you have a lot of sun it will cause the growth of green algae.
In order to offset the sun and extra feedings, you need to have lots of plants that take the nutrients that the algae need to live on.
As well as oxygenating plants (the most important), you need plants that cover a large area of the surface of the water; Water Lilies and the tiny plants that multiply like crazy.
In the spring and when you first set up, the green algae give the pond a pea soup appearance. But, when the other plants take over, overnight the green algae disappear.

There may be circumstances when one or more of the equipment discussed might help the situation. All I can say is that I have never needed any of this stuff nor have any of the other people that keep ponds that I know needed it either.