I got board today, and I have been toying with the idea of a hot wet/dry for my koi tank(another story kinda sad). I saw that I had and air pump, old hot filter and some CC sitting around so I decided to put them together. Basicly I just put crushed coral in the spot between the second filter and the exit with a airstone below it. I do need to put some foam filter stuff on the exit to keep it from flowing out. This was just a board thing to try. Its going on my LR seeding tank(where all my DIY's go). I will get better pics soon when I feel like finding my dig.