Originally Posted by
daleroark
Thank for the input.
All the threads I see tell me to put a grate in. I still can't see where it does any good as air will be on all sides of tank and will fluidize the bed. The water will work its way up ok through the rock.
I have never seen a filter that works in the upward direction. Almost all municipal water plants are downflow filters. They usually have two or three feet of water on top. The media rests on gravel that surrounds the drain pipes.
Leopold has a site that explains a multi media filter.
I will try and let you know how it works.