Whether or not to run a fuge is a huge debate that really doesn’t have a firm concise answer. When I get asked, “should I run a fuge” or “why do some of my sumps not include a fuge,” I like to ask two questions. What are you trying to accomplish by running a fuge and how much space do you have?
One of the most important items to sort out first is the purpose of your fuge. Are you using it for nutrient export or are you using it as a safe haven for delicate animals and pods. Just like sumps, fuges are not all the same and the design varies depending on the purpose. To not have a clear direction towards nutrient export or safe haven will result in a mediocre performing fuge simply because it’s not directly designed to do what you want it to do. Have the right tool for the right job.
Nutrient export is the most common reason people run fuges. I’m also going to lump stability into this same category, because the design is generally the same. Fuges designed for this purpose generally utilize macro algae to remove excess nutrients. Here’s where most get it wrong. Just slapping a sectioned off portion of the sump that water flows through on the way to the skimmer will not provide the proper conditions for your fuge to work properly.
The flow rates for your skimmer versus your fuge are different. Skimmers required a certain flow rate and water run height to perform appropriately. There are dozens of factors that go into maximizing the performance of your skimmer. I’ll save the flow rate discussion for another day, but generally state that skimmers are designed to work in a somewhat brisk pace of flow. Fuges on the other hand required a much slower rate of flow. Since the process of nutrient extraction is based on photosynthesis, the macro algae needs the time to absorb the nutrients before it is returned to the tank. For this reason, I find it best to separate the fuge, either with a completely separate tank or in the sump and just not in the linear path of the main flow of the sump.
Consideration #2: Size. If you enlarge the scale it is pretty easy to see 10 gallon fuge is not going to have any effect on a 500 gallon tank. Take that same scale to a 100 gallon tank and you end up with a 2 gallon fuge. Majority of sumps with a built in refugium have less than a 2 gallon fuge so why would this work any better. Size the fuge appropriately for the display if your purpose is nutrient export. 15-20% should be the minimum.
As equipment obsessed as I am I still love fuges. Every tank I run has a fuge and not a single one is built into the sump. This gives me great flexibility in cleaning and testing out different conditions for nutrient export or housing delicate species. If you’re looking into getting a fuge take the time to decide a reason for it and if you need some help we are always happy to chat.