Do It Yourself Undergravel Filter Plans for a Saltwater Aquarium

  • 01 of 06

    Under Gravel Filter Purpose and Parts List

    DIY UGF Parts. Stan Hauter

    Undergravel filters are probably the easiest DIY project for an aquarium. They work well when you don't want a lot of water movement and are excellent for raising clownfish or seahorses. You can use an air stone in the uptake tube to create the water flow down through the filter, or a small powerhead to create a stronger flow through the filter and water movement in the tank. UGF filtration has been a controversial subject among aquarists for a long time, so consider the pros and cons before making the decision to use one.

    The principle of the UGF is very simple: You suspend the sand or gravel above the bottom of the tank. As water is drawn down through this natural filter, it traps suspended particles, taking them out of the water. You'll need to gather a few supplies to get started. The parts list is for a 55-gallon tank, so adjust the amount of PVC and screen to fit the needs of your tank:

    1. Egg crate: This plastic grid material diffuses overhead lighting. You can find it at most home improvement or lighting stores. Buy enough to cover the bottom of your tank.
    2. PVC pipe, 3/4-inch: For a 55-gallon tank, buy enough to ring the tank and to place a piece diagonally across the center for support. If you have a larger tank, cut pieces to make an X across the center for more support. Take estimated measurements and buy accordingly.
    3. One-inch PVC pipe, 30 inches: Two uplift tubes work great. If you are going to have a larger tank and want to add three or four uplift tubes, you'll need more than 30 inches of pipe. Figure out how many uplift tubes you want, estimate your measured height and buy accordingly.
    4. Male PVC fittings, 1 inch: Buy one for each uplift tube.
    5. Nylon fly/window screen: Buy enough to cover the bottom of the tank.
    6. Nontoxic silicone adhesive: You'll use this to adhere the screen to the egg crate.
    7. Air pump: Buy one with sufficient volume to draw the water down through the substrate and filter plate for the size of your tank.
    8. Air stones: Buy twice the number of stones as uplift tubes. For example, if you have two uplift tubes, buy four air stones. The extras are for replacing worn out air stones when needed.
    9. Air hose: Ensure that you buy hose that has the correct diameter to connect the air stones to the air pump and long enough to make a line from the bottom of each uplift tube to the air pump. You may need a T air hose connector if the air pump only has a single air outflow hole.
    10. Filter media (gravel/substrate material): Buy material with a course texture and enough to create a 1-inch layer on top of the filter plate.
    Continue to 2 of 6 below.
  • 02 of 06

    Cut the PVC

    DIY UGF Bottom. Stan Hauter

    Cut two pieces of the 3/4-inch PVC to fit the front and back of the bottom of the tank. Cut two pieces to fit the ends of your tank between the two front and back pieces. Cut one piece to fit diagonally across the bottom from the front corner to back corner or one piece for the middle of the tank from front to back. Place the PVC in the bottom of the tank up against the outside walls. Secure the PVC with a dab of silicone.

    Continue to 3 of 6 below.
  • 03 of 06

    Assemble the Egg Crate

    DIY UGF Bottom Grid. Stan Hauter
    1. Sculpture the egg crate to fit the inside perimeter of the tank; leaving about 1/8 inch between the pipe and the glass. This will allow a little of the media to slip between the glass and the filter hiding the 3/4-inch support PVC.
    2. Carefully cut holes in the egg crate at the back of the tank about 1 inch from the back glass to fit the 1-inch male PVC fittings. If you are using powerheads, cut the openings to position the tubes below them. Once the holes are cut, twist the male fittings tightly into these holes ensuring that they fit securely.
    Continue to 4 of 6 below.
  • 04 of 06

    Insert the Uplift Tubes

    DIY UGF Front View. Stan Hauter
    1. Make the uplift tubes by inserting the 1-inch PVC pipe into the male fittings that are stuck into the holes, measuring to cut them so that they reach about 1 inch below where the water line will be or the appropriate length to fit under the powerheads at the top of the aquarium when filled.
    2. Once cut, remove the male fittings with the uplift tubes attached and set them aside. If you want to create a current in the tank -- when using air stones -- you can install PVC L's on the top of the tubes and point them in the direction you wish the water to flow to go. If you plan on doing this, drill a hole just big enough to fit the air hose into the top of the elbow, push the air hose through and attach the air stone from underneath then attach the elbow to the uplift tube.
    Continue to 5 of 6 below.
  • 05 of 06

    Fit the Fly Screen in Place

    DIY UGF Uptake End View. Stan Hauter
    1. Cut the fly screen to fit the top of the egg crate, then use silicone to attach it to the egg crate. Let the silicone cure for 24 hours. Overlap the fly screen and wrap it around the edge of the egg crate inward to about 1/2 inch on the bottom side. Use silicone to adhere the egg crate; let it dry, then use a needle and monofilament fishing line -- about 15-pound test -- and sew the fly screen to the egg crate, using a running/basting stitch through each of the egg crate squares.
    2. If you are keeping wrasses or other fish that like to burrow in your substrate, over a period of time they can separate the screen from the egg crate. This results in a lot of the gravel getting underneath the UGF plate instead of remaining on top where it belongs. Sewing the fly screen to the egg crate helps to avoid this problem.
    3. Once you have attached the fly screen to the egg crate, cut the fly screen out of the holes where the male fitting/uplift tubes go, leaving about 1/2 inch around the inside of the hole. Twist in the male fittings/uplift tubes into the holes and place the completed filter plate on top of the 3/4-inch PVC pieces already positioned on the bottom of the tank.
    Continue to 6 of 6 below.
  • 06 of 06

    Install the Air Lines

    DIY UGF Completed - Top View. Stan Hauter
    1. Rinse the substrate material to remove any fine sand or sediment. If you do not, it will end up clogging the filter plate over time. Distribute the substrate material evenly on top of the assembled filter plate.
    2. Make the air lines by taking an air stone and attaching it to one open end of the hose. Lower it inside one of the uplift tubes so that the air stone sits level with the male fitting ring then cut the air hose to the appropriate length to reach the air pump, or T connector if you are using one. Repeat this process until you have made one air hose line for each uplift tube. If you have trouble getting the air hose to raise up out of the uplift tube when it is running, place a weight around the area where the air hose attaches to the air stone. A soft lead fishing line weight works well, but it should fit halfway around the hose and plastic connector part of the air stone when pinched on so that it won't fall off.
    3. Fill the aquarium with salt water and plug the air pump in.
    4. After your tank has cycled, start a regular maintenance routine. Follow up with a good filter maintenance program.