""The water surface of your main pond should be at the same level of the patio, or higher; preferably higher. So the edge of the pond wall should be higher than the patio level. It needs to be at least a little higher than the patio level in order to keep the leaves and dusts out. ""
I was thinking the same. I might rised the pond water level up to around 2" over the patio pavement and my wall will be 6" above patio pavement level. The reason I want the box filter b/c this is the only filter that I know how to build and cheap. I've read and watched on youtube on how to built koi filter but I can't see how it works better than bog filter base on my limitted knowlege + they're so hard to hide and require weekly clean out ?. But anyway I am still do research on DIY filter.