Hello! I am thinking about building a sump that is 25 inches long, 5 inches wide, and 19 inches high. I will be putting lava rock, gravel, and sponges in it. I will also be planting lucky bamboo (which is a bog plant) in the sump to act as a nitrate filter. This sump will be filled to the top with gravel and lava rock, so there won't be that much water in it. I am planning to build a box out of plywood and line it with pond liner. I will then cut holes from one side of the box and build a waterfall from it. The water pump will pump water into it so it will basically have the same design as a HOB filter. The pump will pump water into the middle of the sump and water will go out from the 2 ends as a waterfall. I am not sure what the thickness of the wood should be. Any ideas? I will be gluing everything together with aquarium silicone. Is there any better material to build it out of other than wood? It have to be cheap and easy to obtain, since I am not exactly rich. Help is appreciated!