A well designed aquaponics setup with a balanced fish:plant ratio that uses high quality fish food actually shouldn’t need a biofilter. The circular relationship between the fish, the bacteria and the plants provides all the filtering you should need. You do need to ensure that the water circulates evenly, and that there’s plenty of surface area for bacteria to colonize and transform fish waste to plant food. Grow media is usually the ideal place for bacterial colonies, especially if you’re using a substrate like expanded clay pellets or LECA. The microscopic nooks and crannies in these materials present enormous surface areas for bacteria to settle on so they can happily process all the water that passes by. In a typical pond or aquarium, the media used isn’t selected for its high surface area, and a biofilter is required to give the bacteria a place to live and work.
Aside from providing a home for bacteria, bio filters and other aids, like mechanical filters, settling tanks, and so on, are generally included in aquaponics systems to solve problems that don’t need to be there in the first place, but are commonly used in horticultural or aquaculture systems. In a typical aquaponics setup, you’re unlikely to have multitudes of leaves, branches or grass clippings falling into your tanks and overwhelming the natural cycles. Ideally, you’ve got a properly balanced fish to plant ratio and you’re not using any chemicals such as algaecides that could potentially damage your bacterial colonies. You shouldn’t have sediment or undigested solids circulating through the system that might clog up your equipment, so none of these add-ons should be needed. Make sure that you’re feeding a high quality fish food, and only as much as the fish actually need. Uneaten or undigested particles of food may be invisible to the naked eye, but they can quickly throw an aquaponics system out of balance and lead to poor water quality, poor plant growth and stressed fish. The best response to this situation is not to start loading on extra filters, but to improve the quality of your fish food.
