Because so many fish and corals require pristine water conditions, filtration of our reefs water is a very important and very expansive aspect of the marine reef keeping hobby. All the types of filtration can be broken down into mechanical and biological. Mechanical filtration are going to be your canister filters, protein skimmers, uv sterilizers, etc etc. Biological filtration includes your refugiums, algal scrubbers, (click here for more information on algae scrubbers), your rock, and deep sand beds.
Biological filtration uses natural processes to reduce unwanted chemicals such as nitrate and phosphates. Certain types of macro algae’s, such as mangroves, chaeto, culpera, etc use these nutrients as food to grow. As the algae’s grow, they take up the nutrients and leave our water quality good as new. Of course the effectiveness of your bio filter relies on the size compared to the total water volume of your aquarium. From my own research, a refugium 1/10th the size of your total water volume is sufficient, but results vary and there are many methods to chose from when making your bio filter.
On my aquarium, I built a refugium/sump combination out of an old 15 gallon aquarium. I sectioned the tank off with glass baffles and some aquarium safe silicone from home depot. Here are some pictures of my setup and design.
The refugium portion (the larger part of the sump) came about to be just about 5 gallons. When installed, it will hold macro algae and a deep sand bed. The smaller side will house my protein skimmer and the overflow from the tank. It will flow through the bubble trap (3 glass panes close together) and into the center section, which holds the pump for my return to the main aquarium as well as a pump for my phosban reactor.
here are a few more pictures of what the sump looks like after I installed it in my stand. Click the images to expand them.
Since installation, I have definitely seen a drop in nitrate and phosphate in my reef aquarium. Currently in the refugium are about 20 mangroves, a nice size ball of chaeto, and a small strand of some grape culpera. All of the algae are doing well and seem to be growing very nicely. I have also placed my yellow watchman goby inside the fuge because he was looking a little sick, as well as a few crabs that were messing with snails and coral.
I will try to post some diagrams of the actual build into the stand and show how the flow through the refugium/sump works. Also, if you are planning to take on a build like this yourself, please make sure that the silicone/glue you use is reef safe. Look for things that say 100% silicone and FDA approved. If your silicone says anything about mold inhibitors, stay away, it is not reef safe, even if it says 100% silicone. If you are still unsure, look at the types of silicone your local hardware store sells and look them up online to see if they are safe. Also, Prepare to get a little messy if it is your first time working with silicone.
Common brands of reef safe silicone are: