Canreef Aquatics Bulletin Board - DIY 30"X 8" skimmer

I hope some of the Links work if not it could be the server

ok Elias
think about counter current for a good DIY what about this I would like to introduce what the proteins and other organic molecules are doing when they come into contact with an air bubble:

http://www.hawkfish.org/snailman/ima...ign/bubble.gif

The circle in the above diagram is an individual air bubble released by the airstones inside the protein skimmer. The smaller the air bubble the better as the smaller the air bubble per unit volume of air injected, the more water/air surface area is produced. Think of this as two identical containers: on containing a given mass of pea gravel. An identical container holds an identical weight of playsand. Which container has more surface area of the particles inside it: the pea gravel or play sand? The correct answer is the play sand. As the bubble travels up through the water column, the elecrically charged protein molecules (which contain elecrically polar and electrically nonpolar regions) are attracted to the air/water interface of the bubble. The polar regions of the molecule (made up of nitrogens, oxygens, etc) are attracted to the air/water interface and these polar "tails" stick out away from the air bubble into the water column. The nonpolar regions stick out into the air bubble because it does not "like" to be in contact with the polar solvent (i.e. water). If you could look at this bubble under high enough magnification down to the molecular level, the entire air bubble would look like a fuzzy ball with protein tails and other electrically charged tails sticking out from the surface of the air bubble. The polar regions outside of the air bubble stabilize the air bubble very much like a soap bubble in your kitchen sink or your washing machine. This is why a foam begins to build up at the surface of the skimmer. As the protein laden bubble reaches the top of the protein skimmer, the proteins begin to accumulate which creates a stable foam bubble. These stable foam bubbles take a long time to pop. Thus, the proteins slowly are concentrated at the top of the skimmer where they are slowly pushed through the "throat" of the protein skimmer and into the collection cup.

Different Skimmer Designs:
With all the different skimmer options out there, it's sometimes hard for the person new to the hobby to understand all of the "lingo" when it comes to skimmers. Basically, there's two main areas that are of focus when people talk about their skimmers: water flow and air injection method.
With water flow, there's two general methods:

co-current
counter-current

These two terms simply explain which way the water is flowing with respect to the flow of the bubbles in the skimmer. A co-current skimmer has the water flowing in the same direction as the bubbles and a counter current skimmer has the water flowing against the upward flow of the bubbles.
For air introduction, there's many methods. Four of the primary methods are:

air pump / airstone
venturi
downdraft
beckett

The air pump / airstone method is pretty straight forward: an airstone attached to a good air pump is situated at the bottom of the reaction chamber and water flows from bottom-to-top or top-to-bottom (co-current vs. counter-current) as pictured above. A venturi skimmer uses a venturi device to suck air into a water line as water travels thru a venturi device. A couple good pictures and websites on venturi skimmers can be found at http://w3page.com/fishline/gif/ventskim.gif, http://mars.reefkeepers.net/Articles/SuperSkimmer.html. A downdraft skimmer utilizes a pressure rated pump to push a high volume of water into a tall tube filled with bioballs. This tube has a valve attached that allows air into the mixing chamber where the water impacts with the bioballs in the tube. Geo has a couple nice shots of his DIY downdraft skimmer: http://www.homestead.com/geosreef/downdraftskimmer.html and Peter Z has a very nice cross sectional schematic of a downdraft skimmer: http://w3page.com/fishline/gif/ddskimpz.jpg. A beckett skimmer works similar to a downdraft skimmer except it uses a beckett pond injector and a pressure rated pump to make a great deal of foam. A couple good URL's to look at for how specifically a beckett is setup is: http://www.eparc.com/diy/skimmers/ian/hsa.shtml, http://nucalf.physics.fsu.edu/pfohl/Fish/Diy/hsa.gif.
By far the most efficient way to run a skimmer is in the counter current flow condition as it causes the bubbles to have a longer contact time with the water compared to the co-current flow condition. It was estimated by Escobal that some proteins take upwards of 2 minutes contact time with air to attach properly. Now when it comes to air introduction method, methods #2, #3, and #4 all use the pump powering the skimmer to introduce air into the skimmer at the same time the pump pumps water into the reaction chamber. While this works just fine, it does limit the user to not being able to independently control water flow rate through the skimmer and the air volume injected into the skimmer reaction chamber. With options #2-#4, if a person were to decrease the water flow through the skimmer the person would also decrease the amount of air injected into the reaction chamber. Option #1, however, is uniquely different from the other 3 methods as it *does* allow independent control over water flow through the skimmer and air flow rate into the skimmer. Because of this, counter current air driven skimmers are among some of the most efficient skimmers out there when designed properly. They are also some of the most energy efficient skimmers available. Many of the larger venturi, downdraft, and beckett skimmers require large energy hogging pumps to produce enough flow to suck air into the skimmer reaction chamber.