I made mine from PVC
. I used 3" PVC
at 24" tall for the main reaction chamber and .75" PVC
for internal standpipe for the return. 3"-2" reducer for the top and I had some 2" PVC
laying around. That was used for the collection tube up into a plastic bowl I had also. The base is a 3" PVC
toilet flange that's capped off. Vinyl hose and fittings were used as bulk heads. The Input and return are both at the top. This forces the water to travel down through the bubbles traveling up and back up through the stand pipe and out. This is called counter current flow. It uses a 90-100 gph
power head(can't remember which) to cycle water at about 1.5 gal
/min. They say that the flow through your skimmer should be double the tank volume. IE my 55 gallon should have a 110gph flow through the skimmer from what I have read. Your goal is to have the water contacting the bubbles for about 1.5 to 2 mins. Closer to 2 the better. This allows optimal adhesion of the proteins in the water to the bubbles. My design is made to stand behind the tank I'll add a pic in a bit. This design is tough to dial in as far as adjusting wet/dry skimming. It's running wide open and skims slightly dry, if I had to re do it I would put the return leaving the main chamber lower on the tube and have the stand pipe out side the main chamber. This will allow you to adjust the height of the skimmer level by adjusting the standpipe height, the pic is without the collection cup. I used two Red Sea wood air stones and a pump I had already to make bubbles.
hope this crazy long post helps.