Overview

Many people have asked me how I make wooden air diffusers for my large (4' to 5' deep water column) Counter Current protein skimmers.  The reason I make them is that I could not find a convenient source for a 6" long diffuser, and the 3" long diffusers that were readily available did not create enough bubbles for the skimmer to work properly and if I used two 3" diffusers in each skimmer, my monthly air diffuser bill would be over $10.00.  So, I was forced in make my own if I wanted my skimmers to function effectively.  The following plans are for a 6" long air diffuser, but they can be made to any reasonable length.

Materials:

 An air diffuser in a protein skimmer must produce large quantities of the smallest bubbles possible for the skimmer to effectively remove nutrients from your salt water. The type of wood becomes important due to the required bubble size.   My research for the proper materials led me to lime wood as that most commonly used.  However, the search for lime wood in the Pittsburgh area proved fruitless (no pun intended) so I had to search for an alternative.
Other woods that have been suggested include Bass wood and Oak. I had an e-mail exchange with Albert Thiel recently, in which he told me that he tested several types of wood and found that oak produced much smaller bubbles, but required a stronger air pump, so I will experiment with Oak in the near future.

The second most commonly used wood was basswood, and I was able to find it at the local Woodcrafters supply shop.  I purchased a piece of 1" x 6" x 6' long basswood board for about $7.00.  Look for a real fine end grain on the wood.  The finer the grain is in the wood, the smaller the air bubbles.
Important:  The length of a diffuser can only be made to whatever the width of the boards are available to you, since they only function when cut across the grain of the wood, not along the length of the grain.  The widest basswood board I saw was 8", so from this board I could make a 7.5" long diffuser.

The only other component necessary was a plastic nozzle to attach the airline tubing to the diffuser. Unable to find an easy source for these, I began to recycle the old ones I had removed from the old Coralife and TFP air diffusers I used to buy.  These have a pipe thread on the end that allows them to be easily installed and removed from your diffusers.  I have tried other types of airline nozzles, one in particular has a plastic insert with a rubber stopper on it that I found difficult to install and reinstall.

Tools:

I've found that the following tools make the job easier, but others can be used.

    1. Small drill press. (6" travel preferred)
    2. Table saw or band saw.
    3. 10/32" drill bit at least 7' long.
    4. Drill press vise to hold the work piece firmly and parallel to the drill bit.
    5. Sandpaper - 60 and 150 grit.
    6. Wrench or pliers to fit plastic airline nozzle.
    7. Safety glasses and work gloves.

Instructions:

    1. The 1" x 6" board actually measures 0.75" x 5.5", so I set the rip fence on my
        table saw to 0.75" and proceeded to cut the wood across the grain into
        0.75" x 0.75" x 5.5" long rectangular blocks.

    2. Check the blocks for splits, cracks or knots and discard any that
        have these defects in them, because they won't work properly.  I managed to
        make about fifty good blocks from the 6' long board.

    3. Next, clamp one or several blocks in the vise (depending on the vise size),
        making sure they are mounted as perpendicular as you can make them,
        so that you drill a hole that is not crooked. Crooked holes will give you
        non-uniform bubble dispersion from the finished diffuser, and will
        reduce its life span.
 
    4. Proper centering of the hole in the block is also important. The easiest
        way to be sure the hole is centered is to draw two pencil lines from
        diagonally opposite corners on the end of each block. This forms
        an "X" on the block and the intersection of the two lines of the "X"
        is the exact center of the block.

    5. Move the vise with the blocks under the drill press.  Install the 10/32"
        drill bit into the drill press chuck and set the length to 5.0 inches.
        This can be done by putting a piece of tape on the drill bit at the 5.0 inch,
        dimension or setting the stop on the drill press to the proper length.

    6. Center the block under the drill bit at the "X" on top of the block and
        drill the hole into the block, make sure to back the drill out several
        times to remove chips, or the chips may clog and crack the block.

    7. Once the drilling is done, I remove the blocks from the vise and sand
        them smooth to remove burrs etc.  I sometimes place the block back
        onto the drill bit and sand it while it spins on the drill...easier, but not real safe.

    8. Lastly, it's time to install the plastic nozzle for the airline tubing.  The easiest
        way to do this is to rinse the block thoroughly in tap water to remove sanding dust
        and to clean any chips from the hole.  While the block is still wet, place it in
        the vise and using the wrench and a little pressure, screw the plastic nozzle into the hole.
        This will sometimes be difficult to get the thread started, but with
        practice it gets easier.  The important thing is the block must be wet.
        When it dries, the nozzle will be nice and tight.

     9. If you want to go the extra expense, you can purchase a pipe tap from
        the local DIY store and tap the hole for the nozzle, which will make
        installation a breeze.  Just take the nozzle to the store and ask for a tap
        of the same thread size.

A few final notes:

       When the air diffusers dry, especially the longer ones, they have a
        tendency to warp or twist slightly.  This doesn't affect their performance,
        but can be avoided if the blocks are clamped flat until dry.  If you have a
        good selection of wood to choose from, look for a more vertical end grain.
        This will help reduce any twist or warp tendencies.

        I replace my diffusers once a month to keep the skimmers operating optimally.
        The cost to make these diffusers is inexpensive, so the frequent changing
        does not become an expense issue.

        Since my skimmers are 4' to 5' deep, I have had to use air pumps with higher pressure
        and volume output.  The following pumps worked well:

                1. Tetra Luft pump
                2. Wisa 120
                3. Wisa 200

        Future plans include oak diffusers and cylindrical wooden diffusers.  I will
        report my findings on these when available.

 
      Doug Kevis
         reefman@voicenet.com
         http://www.voicenet.com/~reefman
        July 8, 1997