World's Ugliest Protein Skimmer
After reviewing many sites on do-it-yourself (DIY) protein skimmers and finding them needlessly complex and far too pretty, I designed this skimmer to be built and used by us "normal" folk.  It's ugly as sin, but the advantages of this design are:

  • The air-water interface is created by the impeller of  a single powerhead.  Contact between microbubbles and water is prolonged.
  • No air pump or air stone is needed.
  • The air-water mixture enters the bottom of the skimmer and is separated within the 2" diameter PVC tube.  Foam rises to the top of the 2" tube by buoyancy, while water flows down and into the 4" outer tube.  Remaining bubbles are also separated in the 4" tube.
  • Unlike other systems, this one is not pressurized.  That is, the 2" tube / collection cup rests inside the 4" tube.  Water drains by gravity back into the tank.  I believe this is one reason why this design produces such a nice, dry foam.
  • Makes a nice dry foam.  I have seen other plans that have a drain in the collection cup.  This is a bad sign because good foam is dry, light, and fluffy.  You can see from the photo that my foam is so dry and fluffy that it forms a peak, not a puddle. (Sorry for bragging, but I feel like a proud parent.)
PLEASE NOTE: For clarity, I have shown the inlet and the outlet on opposite sides in this drawing.  You will find it easier to put them both on the same (or near to the same) position on the real item.  You can see this placement in the photograph.
3/4" PVC pipe
It's inexpensive, so just get an 8 foot length or so.
2" PVC pipe
You will need enough to extend the height of your skimmer.  It goes from just above the height of the inlet and extends through the 4"-to-2" reducer (collection cup).
4" PVC pipe
I built mine about 36" tall.  Remember that your pump or powerhead will have to be strong enough to raise a 4" diameter column of water the height of your skimmer.
3/4" barb to MPT
MPT means male pipe thread.  These join flexible tubing (1) from the powerhead to the ball valve and (2) from the outlet to flexible tubing and back to the tank
3/4" ball valve
Regulates flow into the skimmer.
3/4" MPT adapter
To join ball valve to elbow.
3/4" elbow
The elbows that are shown attaching to the walls of the 4" pipe are connected to short pieces of 3/4" PVC pipe.  The pipe passes through the wall of the 4" pipe via a 1" hole that will need to be slightly enlarged (Dremel tool is recommended).  The elbows themselves do NOT pass through the pipe.
3/4" elbow to FPT
To join outlet to barbed adapter.
4" to 2" reducer
This acts as the collection cup.  You will need to grind or sand down the ridge inside this piece so that you can slide the 2" PVC pipe through it.  I used a Dremel tool.  This will be the most labor-intensive part of the assembly.
4" test plug
Used as the bottom of the skimmer. You may use either a test plug or a cap.
1" drill bit
To drill 2 holes in the main skimmer column (4" PVC pipe).  You will find that 3/4" PVC pipe has an external diameter just a bit bigger than 1".  You will need to sand the opening a bit larger to accommodate the pipe.
I used a Penguin 1140. I adapted it by drilling a hole in the intake just before the impeller to accommodate the venturi (air) tube.
Primer and glue for PVC, and silicone sealant.
Sand all joints before priming.  Follow directions on PVC glue.  Seal the inlet and outlet to the skimmer with silicone.
To assemble:
  • Cut the 4" diameter tube to whatever height you prefer. The one I made is about 36" high.
  • Drill 1" hole in the bottom of the 4" tube and sand or grind SLIGHTLY to accommodate 3/4" PVC pipe.  Allow enough space on the bottom to accommodate the bottom of the skimmer which can be made with either a "test plug" or an "end cap".
  • Dry-fit the inlet assembly (2 elbows and a 3/4" PVC pipe connector) in the bottom of the skimmer so that the 3/4" PVC riser is in the center of the skimmer.
  • Drill 1" hole in the top of the 4" tube and sand or grind SLIGHTLY to accommodate 3/4" PVC pipe.  Place the hole about 2" down from the rim of the 4" pipe so that you have some room for overflow.
  • Dry-fit the outlet assembly. 
  • Place the 4"-to-2" reducer on the top of the skimmer. You can make a good collection cup by adding about 5" of 4"diameter pipe to this as shown in the picture below.
  • Cut the 2" diameter pipe so that (a) its bottom is just above the inlet tube and (b) its top is just below the rim of the collection cup (i.e. the 4"-to-2" reducer plus a bit of 4" pipe on top).
  • Grind down the rim on the inside of the 4"-to-2" reducer so that you can pass the 2" diameter PVC pipe through it.
  • Dry-fit the 2" pipe into the collection cup (hereafter called the collection assembly), then dry-fit the collection assembly into the skimmer so that the 3/4" riser passes through the center of the 2" pipe.  Ensure that the reducer rests nicely on the skimmer as shown below.
  • Glue the inlet assembly and riser.  Remember that you are working in a confined space, so think about what you need to be gluing first. Seal with silicone.
  • Glue the bottom of the skimmer on.
  • Glue the outlet assembly and seal with silicone.
  • Cut and glue remaining parts.  DO NOT glue the collector assembly to the skimmer body.  This way you can take it out.  If you have overflow, you need to decrease the flow into the system.
  • Drill hole in intake side of powerhead and insert included air tubing. You don't need to glue or silicone this, just make sure the hole is exactly the right size.
  • Turn it on and watch it foam.
My experiments show that finer bubbles are produced if you introduce the air BEFORE the impeller.  Note the plug on the manufacturer-supplied air intake just to the right of the clear flex tubing on the outlet.

The production of foam will depend on the following variables that you will have to adjust:

  • The amount of water in your tank, sump, or live-rock curing vat (because this affects the height of the "head" of the pump)
  • The amount of air coming in the inlet (you can choke the pump with too much air)
  • The flow of water (I find that I don't need to use the ball valve at all)
  • The position of the skimmer relative to the water level in the tank (again because it affects the height of the "head" of the pump).

Ugly, yes, but all in all it should cost you about $40-$50.  It works as well or better than my $150 protein skimmer. In addition, I have to say that there's no magic to this design.  If you change it or adapt it, it should still work.