After ten years of playing around with various aquaponics set ups, I finally came to the conclusion that the best option for both economic viability and best management practices for both fish and plants was to separate the two systems. As I have mentioned in other places, a part of this choice has to do with a desire to farm fish at a more intensive level. I really love raising fish, but I also want to raise enough fish to both eat and sell them. For me it doesn’t make sense to have them as simply a plant fertilizing machine.

A part of me wrestled for years with a desire to keep this interconnected symbiotic relationship of plants and fish. But natural systems have a massively lower stocking density than even the least stocked aquaponics system.

So in order to better manage both sides of my system, I use a highly efficient solids filter, and regularly empty it into what has been termed either a nutrifier (a system to turn the fish waste into nutritious plant food) or digestor (a system to digest the nasty waste in order to make it palatable for plant life). Personally, I like the term nutrifier. It just somehow sounds nicer.

The nutrifying system is based on common waste and septic disposal systems. The best combination I have found is a 3 tank system in which the fish waste runs into a “stew” tank where it basically sits in an anerobic state and breaks down. As additional material is regularly added, the waste eventually overflows into a second aerobic tank. This tank is constantly agitated with oxygen, turning the water over and creating a different bio-environment. This tank feeds into a third sump tank which houses a pump and directs water into all the grow beds. Water circulates through the various grow beds and finally dumps back into the second nutrifier tank, where it is recharged with nutrient and then makes it’s way back around the plants in a continuous feeding cycle.

Some aquaponics designers only use a single aerated tank, rather than both an anerobic and aerobic. This is essentially the purpose of what is being called a mineralization tank in some recent design terminology. But if you have a lot of waste from a significant number of fish, then the three tank nutrifying system is the most effective, once set up requires very little maintenance, and allows a host of management possibilities.