 The first component is the aquarium that houses the fish. In this case, we're working with a 15 gallon aquarium that has about 10 gallons of water in it. But when you add the water in the other components, the total amount of water in the system is a little more than 15 gallons. We use 3, 4 to 6 inch koi as the engine for our aquaponic system. These fish start the process of converting feed into nutrients that can be used by the plants. We feed the fish small pellets of 36 to 40 percent protein catfish feed that they can easily swallow. We feed them daily with an amount of food that they will clean up in 60 seconds or less. You don't want to have uneaten feed in the tank as it will clog the pumps and filters. This feeding process ensures that the fish get adequate food and it creates enough nutrients for the plants. There's a small fountain pump that constantly lifts water from the aquarium into the second component, which is the mechanical filter. The mechanical filter consists of a 1 gallon bucket nested inside a 5 gallon bucket that is held in place with a plywood board. Inside the 1 gallon bucket is a piece of 4 inch PVC pipe with holes drilled in it that is wrapped in a layer of filter material. The water is delivered to the bucket so that it must pass through the filter material before flowing over the stand pipe into the 5 gallon bucket below. The stand pipe in the 1 gallon bucket directs water to the bottom of the 5 gallon bucket that can contain additional filter material. Once the water fills the 5 gallon bucket, it overflows into the third component of the system, the plant tank. The plant tank is a plastic box filled with expanded clay balls that serve as media to hold the roots of our Okinawan spinach plants. This media also provides surface area for beneficial bacteria that convert the ammonia produced by the fish first into nitrite and then into nitrate that the plants can use for food. As we are growing indoors we use an LED light above the plants to provide supplemental light. The plant tank contains an overflow pipe that is covered by a bell siphon that controls the water level in the tank. The water fills the plant tank until it reaches the top of the overflow pipe. Once the water starts flowing over the top of the stand pipe inside the bell siphon, it draws the air out from under the cap which starts the siphon causing the water to flow quickly out of the plant tank. When the water level reaches the air inlet on the bell siphon, air is pulled into the cap and breaks the siphon. And then the process starts over again. We monitor the water quality in the system using some simple sensors and test strips. These sensors continuously monitor the ammonia and pH levels and provide a quick visual check to make sure the water is suitable for the fish and plants. We also periodically measure the hardness, nitrates, nitrites, and alkalinity using these handy test strips. A small air pump and air stone ensure that the fish and bacteria will always have plenty of oxygen.