A bell siphon works by creating a vacuum. First, you'll need a pump to get water from your aquarium up to your growbed. When the water level reaches the top of a vertical pipe in your grow bed, water will begin to flow down to the fish tank.

Adding a covering or "bell" over the pipe, whether it be a larger, capped pipe or simply a glass from the kitchen, will allow the creation of a vacuum: Water will fill all available space beneath the bell, leaving no room for air. This will start the siphon.

In order for the siphon to stop and the process to start over, the bell will need to be tall enough for the vacuum to "break" when the water level in the grow bed gets low--otherwise the siphon would continue to operate indefinitely.

A funnel-shaped piece attached to the top of the smaller pipe will assist with this process by causing water to move more quickly through the siphon, draining the grow bed at a faster rate than it fills.

Getting the right size for all the pieces may require some trial and error. First, decide whether your grow bed will be directly above your fishtank or on a shelf or table nearby. For a bell siphon to work, the grow bed must be higher than the aquarium. You will need a minimum of three pvc elbows and four lengths of the smaller diameter pvc pipe (I used 1/2in). The glass or pipe and cap that you will use to create the vacuum should be two or three sizes larger (in my case, 2in). An easy way to create the funnel is to use a pvc connector that takes that takes the smaller pipe up one size. Unfortunately, because the pipe will be connected at the bottom of your grow bed, you will also need to install a plastic bulkhead to prevent leaks. Look for one the same diameter as your smaller pipe.

PVC pipes, elbows, and other connectors can be found at any hardware store and cut to size using a cheap hacksaw (≈ $4). If you don't yet have a grow bed or aquarium, a large sterilite or other foodsafe plastic container can be an inexpensive, basic solution. You can purchase a fountain, statuary, or aquarium pump online or at your local hardware store. A pump with a built in filter is preferred, though not strictly necessary as your plants will be doing most of the filtering themselves! Make sure to get one strong enough to pump water through a pipe over your grow bed. The hardest part to find will be the bulkhead fitting, as these are not frequently available at hardware stores. You can find one at an aquarium store or online.

Bell siphons rarely work on the first try. Be prepared to experiment until you get the setup just right, and don't get discouraged if it takes time. Use the tool below to practice building a bell siphon, without all the mess!