In an aquaponics system, water is pumped from the fish tank and into the grow bed. Bacteria breakdown fish waste into nitrogen, which is taken up by the plants and used to grow. The clean water is then returned into the fish tank. Through this process, an Aquaponics system uses just 10% of the water that traditional agriculture requires.

With regards to the ratio of grow bed to fish tank, here's how you can calculate it. Fish density should be kept at no more than 1 pound of fish per 3 gallons of water. Now, for every 6 gallons of water, you should have about 1 square foot of deep grow bed (about 12 inches deep). This is to ensure an adequate fish waste to plant biomass ratio. Therefore, you will be having about 2 pounds of fish for each square foot of deep grow bed area. However, note that this is a maximum number. If you are just starting out, it is safer to opt for one fish per 5 to 10 gallons of water. As a rule of thumb, use a fish tank to grow bed ratio of 1:1 (by volume).

It is safer to have a higher grow bed: fish tank ratio than the other way round. If you have too little grow bed, there won't be enough bacteria to break down the fish wastes as they accumulate, and soon enough the fish and plants will start dying. You should use a grow bed that is about 12 inches deep and definitely nothing less than 9 inches.

When setting up your system, the water level in the grow bed should be about 1 inch from the top, as the top of the plants should not be wet. In addition, this will ensure that there is no direct sunlight on the water, which would in turn cause an algae bloom. Therefore with a 12 inch deep grow bed, you will be looking at about 10 to 11 inches of which are submersed.

An important aspect of a healthy grow bed is dissolved oxygen, as oxygen is essential for proper bacteria (and fish) growth. Plants also require good oxygen levels on their roots. Ideal dissolved oxygen levels for an aquaponics system are those above 6 parts per million. To ensure healthy dissolved oxygen levels, you should incorporate water stone aeration and some water jetting action; you can incorporate the latter in the way the water returns back to the fish tank from the grow beds.