Do you know that you can use the waste products from your fish tank to grow food that you can eat? Well this is obviously a rhetorical question, because you can. This process is called Aquaponics. What is it exactly? It is the combination of aquaculture (raising fish), and hydroponics (growing food without soil). This is a very cool process and you can actually do it in your own backyard, with stuff you can find at your local home store.
How does it work?
Basically, you take the water from a fish tank, remove the solid matter from it, and use that water to provide nutrients to plants that you have floating on foam beds with their roots dangling in the water. The process is very simple, and is self-sustaining apart from some evaporation of your water source.
First you need a fish tank. A simple plastic container that holds drinking water will do. All you need to do is cut it in half, and follow the instructions from your local pet store about raising gold fish or carp. They will advise you of the temperature of the water you need to keep, and the food and environment you need to keep the fish healthy.
Next you need a grow bed for the plants. You can place the plants in a piece of Styrofoam insulation with holes cut through it, or you can purchase a product called "Perlite" which is a volcanic white pebble that absorbs water and provides a growing ground for bacteria.
Simply place the seedlings of the plants into the holes, and allow their roots do dangle through them. You then take the water from the fish tank, and pump it into the grow bed via a reservoir, and allow it to trickle through the roots of the plants where it is then pushed back into the fish tank.
This is a very short summary to give you an idea of how to do this. I am leaving out a lot of the detail.
Why do this?
One reason people do this, is because of the incredible organic plants they can grow. You can grow practically any edible species of plant this way: Lettuce, Jalapeno peppers, tomatoes, etc. They taste great and are not loaded with pesticides.
Another reason to do this is for the fish products. If you create a little larger fish tank, and are a little more aggressive with your system, you can grow fish like: Tilapia, Trout, and even Arctic Char. These are fish that you can eat or even sell.
Finally, and probably the most common reason people do this, is because they can do it. They do it just for fun. If you like to be different, then this may be the project for you to take on. So give it a try.