Yeah, the under gravel method seems to be a bit old school. The only reason I'm using it is to eliminate any HOB
or tubes running out and down under.
I saw a cool way of making your own bio filter on YouTube with a hollow resin rock, about 7" tall. He drilled holes in the top for air to escape, bigger holes in the back for suction cups, a hole in back for air tube with a T fitting. Filled it with a media, used the 3 sponges in the bottom, fine, medium and course, and stuck it to the inside of the glass. I suppose I could put a carbon filter in there, since I will be using the power pumps on both under gravel tubes.
I don't know, should work out.