Fluidized Bed Filters
Adavantages and drawbacks of fluidized bed filters in aquariums.
J. Charles Delbeek
Q. I've been a saltwater aquarium hobbyist for 10 years and have always much pleasure in reading your questions and answers section in Aquarium Fish International magazine. In my 85-gallon saltwater aquarium I have a Red Sea fluidized bed filter for biological filtration, an Aquaclear 300 for mechanical filtration and to hold Ultralife Nitrate Remover, and an Aquaclear 402 powerhead for water movement. I also have one actinic 40-watt tube in addition to two Trichromatic 40-watt tubes.
I use Combisan and calcium hydroxide as supplements, and I do a 20-percent water change each month. In this saltwater aquarium I have a lot of live rock, with purple and red coralline algae, Halimeda macroalgae and a great variety of zoanthids from our coast. I have no corals. The saltwater fish I have are two Amphiprion ocellaris, a Paracanthurus hepatus, a Calloplesiops altivelis, a Chrysiptera parasema and a Stenopus hispidus shrimp.
I'd like your opinion on fluidized bed filters. What are the advantages and disadvantages, and are they good for reef aquariums and fish-only aquariums?
A. Thank you for your letter from all the way down in Brazil! It's nice to know that the hobby has a pulse in your country.
My opinions on fluidized bed filters were printed in an article I wrote for the Aquarium USA annual. Advantages of this type of system include rapid turnover rates, rapid nitrification and a very large filtration capacity in a relatively small space. Drawbacks include erosion of the substrate and the need for oxygen. The water entering these filters must be high in oxygen in order to provide the aerobic bacteria with enough oxygen to carry out their activities.
Once the water leaves the filter much of that oxygen may have been removed. This could easily be solved by passing the water through a protein skimmer before returning it to the aquarium. Because the bacteria rely on oxygen for their survival, any reduction could result in loss of nitrifying ability, such as might occur during a power failure or any other event that would cause a halt in water flow through the filter.
I have no experience with these filters, and my concerns may have already been addressed. These are relatively new designs for small aquariums, and they need to be evaluated over time. I suspect in your system your live rock is probably handling a lot of the waste. As we say in North America, if it's not broken, don't fix it!