Fluidized bed filters - Advantages and Disadvantages
Nowadays in the aquarium hobby there are many forms of filtration available from the suppliers, so sometimes it can get confusing as to which are the right ones to use on your aquarium. We have internal filters, external canister filters, running a sump, wet and dry trickle filters, diatom filters plus an old favorite with many people – the fluidized filter bed.
All of the above filters have their advantages and disadvantages but over them all, the fluidized bed filter makes a great secondary filter to use as a back up for your overall system.
They come into their own with heavily stocked aquariums, planted aquariums and marine aquariums. The great advantage with planted aquariums is the fact that these filters will not reduce the CO2 levels in the water which the plants depend on. Another great advantage of this system is that the maintenance side of them is drastically reduced as they tend to run for much longer periods without clogging and indeed they have the ability to clean themselves.
Internal filters tend to be restricted on the beneficial bacterial count that they can carry, external canister filters if not cleaned thoroughly on a regular basis can be slowed down immensely when they start clogging so a lot of maintenance is involved. Wet and dry trickle filters are basically a glass or acrylic tank with bio balls, live rock, or similar media, where the pumped water basically drops into the filter randomly covering the media but can have a lower bacterial count if not set up correctly.
As the name suggests with fluidized filters the media is held in suspension by a pumped water flow so that every particle of the media will have an exposed surface area to contain the beneficial bacteria need to purify the water of nitrates, ammonia etc.
So basically these filters consist of a pump to create the water flow, a chamber or tank to contain the media, and an outlet to feed the purified water back into the tank.
There are several types of media that can be used in these filters, the most common being sand, white quartz, and even sintered glass. Once any of these materials are in suspension in the chamber there surface area is increased dramatically, every small grain being utilized to its fullest to act as a platform for the beneficial bacteria. There can be anything up to 6000 square feet of surface area in as little as 1 cubic foot of media.
This also means that the size of the chamber can be decreased due to the efficiency, so a filter with a chamber say 3 foot high will quite easily cope with anything up to 1000 liters of water.
As the grains of media are in total suspension they will continually collide with each other in the chamber, thus they can clean off any excess debris while they are still filtering, hence the need for less maintenance and less space taken up by the hardware which is an obvious bonus as in a lot of fish houses, free space is at a minimum. A lot of fish breeders are using this system as a backup, mainly due to the fact of the efficient reduction in ammonia and nitrate levels which can increase rapidly in their growing on tanks as they will feed the juvenile fish high protein diets in order to aid the growth rates which in turn will result in higher fish waste.
Due to their simplicity there are several models on the market, supplied by the big aquarium distributors, which are relatively cheap, compared to other forms of filtration; TMC, Red Sea, Rainbow, Quicksand, and Pentair all produce their own brands. These can range from fifteen to twenty pounds (thirty to forty dollars), but are supplied without the water pump.
But to save the cost of a new model a simple DIY version can be set up with minimal effort. A three chamber sump tank can be used to great effect, raised above the main tanks. In chamber 1 - water is fed by means of a pump, and some sponge media can be added to act as a pre filter, in chamber 2 the sand, quartz media is added, and in chamber 3 - gravity will feed the water back to the tank. Make sure a non return valve is fitted to the water pump as if there is a power failure and the pump gets flooded, the gritty nature of the media can create havoc on the internal workings.
There is a lot of debate as to whether the fluidized systems actually hinder gaseous exchange of the water. As they do not remove the CO2 content, they will not bring oxygen into the water, and indeed the bacteria will consume some of the oxygen. Because of this a lot of aquarists prefer to run an air stone in the main systems to compensate.
Another problem with this type of filter is experienced when a power failure occurs. Although the bacterial colony can recover from this quicker than say a trickle filter, if left they can start to leach toxins back into the system as the media compacts at the bottom, so be prepared to disconnect and lightly rinse the media in aged tank water if the power is of for a great length of time.
As with all biological methods of filtration it takes time to build up a colony of beneficial bacteria, do not expect them to be 100% efficient straight away, they do need to go through a bacterial build up cycle which can take anything up to four to five weeks to accomplish.
Never use this type of filter as your main biological filter, always use them as an additional filter to your present system. They can help out tremendously with heavily stocked tanks, where the food waste, detritus from the fish stocking is larger than normal.
As stated above they are relatively cheap compared to other filtration methods, so overall I think they are a great investment to your aquarium.