6.6 Cycling the System

Cycling refers to the process of establishing the biological filter. This can take between six to eight weeks (Figure 17). Nitrifying bacteria are found naturally in the environment, so the process begins by adding a source of ammonia.

This can be accomplished through adding fish, fish food, or water from a well-established system, or a combination of these. One of the most common mistakes when using fish to cycle a system is adding too many fish initially. This causes ammonia levels to spike, often resulting in fish death. Starting with 20% of the total fish capacity is a good rule of thumb. This allows the appropriate, system-specific biological organisms to colonize. If using a fish-less cycling strategy, household ammonia can be used. It is important to source surfactant-free ammonia, as it lacks detergents commonly added to these products that are unsuitable for the system.

Source: Janelle Hager, Leigh Ann Bright, Josh Dusci, James Tidwell. 2021. Kentucky State University. Aquaponics Production Manual: A Practical Handbook for Growers.