I have a fish bowl that I want to put some red cherry shrimp in, but I wanted some kind of filter for it, and a hob was out of the question. So I found a few different undergravel filters online, but I am too cheap to pay $15+ for one, plus shipping, so before I had to go to work today I dug out some stuff to try to make my own.
I have several of these thin plastic trays for my houseplants, so I decided to cut one to size, drill some holes all over in it and cut space for the plastic tube to fit in.
I put some small-ish stones I got from my garden in the bottom of the tank, placed the cut tray on top, put the tube in the hole I cut for it (and propped it on two o the stones so it wouldn't slide down to the bottom), covered it with gravel and put my plants back in. I then put in an airstone and started it. Once I got home I put my four immortal "feeder" guppies in it. So far they seem happy with their new setup... We shall see how well this works out.