This project outlines the construction of a diy fluidized bed filter. This filter will function quite well and give you years of low maintanance performance. The photo below shows the finished fluidized bed filter and I will outline the construction of the filter futher in this project write up.
This DIY fluidized bed filter is a very efficient biological filter. One of these filters is able to handle the bio-load for nearly 1000 gallons of water. The great thing about this fluidized bed filter is that it can also be used on much smaller aquariums starting at about 55 gallons. Although a sump is not needed to use this filter, it is recommended because it will give you a good place to put the pump.
Before you begin building the filter, take a measurement of the space you have to work with. Make sure that you have enough room for the footprint of the filter behind the aquarium and find out what the maximum available is for the space you have available. The filter in the photo above is about 30" tall. This is probably the minimum height required to ensure that the sand doesn't escape into the aquarium.
Step 1: Begin the construction by cutting all of the 4" PVC pieces to the desired lengths. Dry assemble all of the 4" PVC pieces to ensure you have the proper height for your space.
Step 2: Once the proper height is acheived, you can cut holes in the 4" PVC end caps. When drilling these holes, it is best to get them as close to the center of the cap as possible.
Step 3: After the holes are cut, the bulkheads can be installed. To install the bulkheads, insert them through the holes in the end caps so that the nut and screw portion of the bulkhead will be on the outside of the filter. Make sure to install the rubber washer on the inside of the cap.
Step 4: This is one of the steps that calls for attention to detail. You need to install a section of 3/4" PVC pipe on the bulkhead that goes onto the straight portion of the Y-coupler. This section of 3/4" PVC pipe must be cut precisely. It MUST have between a 3/8" and 1/2" gap from the bottom of the filter when assembled. If the gap is much larger than this, the water flow will be too great and a tunnelling effect will happen through the sand. If the gap is less than this, the performance of the filter will be reduced due to restricted flow.
Step 5: Once all of the measurements are double checked, you can use the PVC primer and cement to assemble the filter. All of the parts except the top cap on the output side can be glued. By leaving this output cap unglued, it makes it much easier to add sand to the filter.
Step 6: After the PVC cement is dried (It will not take long), you can add the sand to the filter. Be sure to wash the sand before filling the filter. This will greatly reduce cloudy water when the filter is turned on. You fill the filter with sand until it reaches the bottom of the Y-coupler.
Step 7: Prime and glue the top cap. Fill the filter with water and look closely for any leaks.
Testing and installation
To test the filter and get it set up for usage, follow these directions. Put the pump in your sump and position it so that the flow control valve is accessible. Install the check valve on the output of the flow control valve. Using a barb coupler and half of the clear vinyl hose, connect the pump to the input of the filter. Connect the other half of the clear vinyl tubing to the output of the filter. This acts as the return to the aquarium.
Once all of the hoses are installed, take the entire assemble outside and use a garden hose to initialize the bed fluidization. The pump will not have enough force to start the fluidization of the filter so this step is neccessary. Once the bed is fluidized, it will remain that way as long as the check valves are installed and properly functioning. If the water will not flow through the filter with the pump, you may have to repeat this step.
Reinstall the filter and connect everything securely with the hose clamps. The filter should now operate but it will need to be adjusted. In oder to adjust the filter, use a flashlight to illuminate the Y-couple area of the filter. Adjust the flow of the pump so that there is just a rippling on top of the sand. If it is creating more than a ripple, sand will be blown out into the aquarium.