I remove detritus from my system overflow water by using a simple mechanical filter that takes advantage of water velocity changes to cause heavier particles to drop out of the flow. Basically the mechanical filter is a labyrinth that forces the water to continually change directions. The labyrinth has areas of stagnation and vortices where heavy particles (and even some lighter ones) will become trapped and settle out.
The settled particles end up on the bottom and in a manifold of PVC pipes that lead to a ball valve. When this ball valve is opened, water is drained off from the bottom of the mechanical filter box. This serves several useful purposes. First, I can drain off detritus without loss of much water by briefly cracking the ball valve. This water goes down the drain in the floor never to be seen again.
Second, I do painless water changes by shutting down my pumps and then draining the contents of the mechanical filter box. This not only clears the detritus that may have collected, but it removes a measured amount of water (about six gallons). I restart the pumps, thereby allowing the box to refill-- shut them down again and drain off the water in the box. Doing this three times allows me to remove just about 25 gallons which is precisely the amount of change water that my water change drums each hold. I then pump my replacement salt water back into the system from the 25 gallon water change drums directly below my skimmer sump by using a submersible pump. I can do water changes without ever getting my hands wet.
A third feature of the mechanical detritus filter is the ease with which I can add chemicals to the water system. Since there is a great deal of churning that goes on within the entry side of the box, I can add iodine and other chemicals to the entry side and be sure that there are completely mixed by the time they reach the Jaubert sump below. A lot of oxygen is also injected into the system due to the water falling from the show tank above into this mechanical filter box (as well as when it leaves the box). Mixing is so good that a small degree of skimming actually occurs with foaming observable at the surface of this input section. The water velocity rapidly slows as it moves through the wide water paths in the box.
The third left-hand section (just before the outflow section) is where I apply activated carbon when I use it (rarely). I have constructed a flat polyethylene screen enclosure that I can place in this section thereby assuring that practically 100 percent of the circulating water must flow through the carbon.
This mechanical detritus filter is constructed from an acrylic display box formerly used to cover a display in the Smithsonian's Air and Space Museum in Washington, D.C. Who would have thought that a 40-year old aeronautical display case would someday be part of a life support system for a coral biome?
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