DIY Undergravel Filter

8.5.2. DIY Undergravel Filter

Below we go into two designs of DIY undergravel filters. The first is a somewhat expensive but robust PVC pipe design. The second design is a cheaper but less robust design that uses a plastic grid from the needlepoint hobby.

DIY PVC Pipe Undergravel Filter

A few commentators have now asked about do-it-yourself undergravel filters made from half-inch PVC pipe. So I’ve come up with a DIY design. But one should be warned, the cost of all the fittings and pipe involved is two to five times the cost of just buying an under-gravel filter from Petco or Amazon. So this PVC pipe design is only for those interested in a DIY project, or in a country where under-gravels are ridiculously expensive (like Canada).

Note there are other designs on YouTube. All these designs seem to just go around the periphery of the aquarium. A few have one cross branch. These designs just won’t do a lot of filtration as most of the gravel will not have any flow through it.

My design has as many cross branches as one can have. This is the basic design:

DIY Under Gravel Filter
DIY Under Gravel Filter

Drill holes a quarter inch apart or cut grooves one inch apart in the PVC cross members. Note if one wants to make a cheaper design it the 8 to 13 tees on the left can be replaced with ten to fifteen PVC caps. This shouldn’t affect the efficiency any.

Key to this design is the modification of the Tees to allow close positioning of the PVC pipe. If you don’t shorten the legs on the tees one will spread the PVC out to the point where I think its effectiveness will be affected.

Modified Half Inch PVC Tees and Elbows
Modified Half Inch PVC Tees and Elbows

This design is especially useful where large fish are involved. An Oscar can remove the air lift on a standard undergravel filter in all of about two seconds. They have far more difficulty with a solid schedule 40 PVC design, especially if the design in buried under four inches or so of gravel.

Making a Plastic Mesh Undergravel

One idea I’ve had for quite a while is to use the Plastic Mesh Canvas sheets that needlepoint hobbyists use to make an undergravel filter. Simply buy the following item:

Plastic Mesh Canvas Sheet
Plastic Mesh Canvas Sheet

It is important to get the large size sheets with the SMALL 2.5 mm. x 2.5 mm holes. Larger holes will let the gravel fall into the mesh. Cut the mesh to the needed size.

Then get some checkers. Yes, I said checkers, the old table game pieces. These:


If checkers are not available, the plastic caps from water bottles will work just fine. Get a good gap-filling adhesive like an epoxy (not silicone, silicone does not stick well to plastic!). Hot melt guns are great. Glue a checker every four inches around the periphery of the plastic mesh. Then glue a checker every four inches across the middle of the cloth. If you are using water bottle tops, use a three-inch spacing.

Then glue several three-inch by three-inch pieces of mesh to one back corner. Cut a hole in the build-up to the size of a riser tube and glue a riser tube in place. This will take some fabricating skill but it is surprisingly easy. You can cut some quarter-inch wide strips and put them around the periphery to seal the gravel out but it really isn’t necessary. You now have a surprisingly cheap undergravel filter.

Note if one wants a higher plenum one can use plastic pot scrubbers in place of checkers, underneath the mesh. This would add to the filtration capacity of the under gravel filter. Just another idea.

Unconventional Hook-ups

Some advocate hooking up a canister in series with an undergravel filter. We DO NOT recommend this. The problem comes if the canister springs a leak (a common occurrence!). If this happens you can literally drain all the water in an aquarium and kill all the fish.

Startpage Aquariumscience

Source: – David Bogert

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