I am building a cement fish pond that will have an assortment of fish. Koi, Talapia, Barra, and a few others. The bog garden part will be a shelf, 30 cm deep running around the circumfrance of the pond. In most places it will be from 30 cm wide to 1 meter. At one end of the pond it will be 4 meters wide. The bog will be cement and filled with gravel. Water will be piped from pond to the back side of bog and flow up threw and over gravel back into the pond. The overall size of the pond is approximately 17 meters X 11 meters.

My question is: What is best,more effecient - to let water flow threw and over top of the gravel or to make gravel deep enough so water can flow only threw the gravel? I like the looks of the water flowing over top of the gravel and it also makes the pond appear larger. However, would it stil be effecient enough to keep water clear and clean? Thank you.

We have a similiar set up in our pond. When we were putting in this pond, DH foamed large flattish rounded stones on end, side by side. This created a similar situation to what you have outlined above. We then put washed pea gravel into this bog/shelf area and planted the water plants directly into the pea gravel.

DH has a pump - about 500 gph that runs from the pond into the bog. The end of the hose that the water comes out, is buried into the pea gravel so that it stays in the pond. Because everything is the same level, you don't really see the water coming out of the bog and into the pond.

This goes a very long way towards keeping the water clean and clear.