i stacked 3 12x4s on each side and bolted them together at the corners. there are extra 2x4s bracing each corner. then i screwed a 4x8 piece of plywood to the bottom. as for the copasity of it i figured it using 8x4x2. the water goes through all the media before it goes into the pond. there are 2 5gallon buckets holding media. for now only the firt bucket has media and the water must go through all that before entering the main can. ill try to get pics of the framing tommorow.