In my environmental science class my partner and I are going to "create" a river ecosystem in a long glass (almost fish tank). We need a type of filter or something which will move water all through it and make a constant flowing current to recreate a rivers movements. I was wondering what type of filter we should use. Like undergravel? Or just a HOB filter? Any ideas? Also we will be putting in it microinvertebrates as well as some minnows. Possibly live plants too. Thanks!