Fish Tank Aquaponics

Gardens Fertilized with Fish Waste

Gardeners know that fertilizing your plants can be a tedious task and fish tank owners know that cleaning the fish tank can be an even more troublesome task. Fish tanks that double as Gardens appear to have solved that problem. Aquaculture aka aquaponics is a system that combines fish farming or a simple fish tank into a hydroponic garden, the two combined are aquaponics. The fish waste acts as fertilizer for your plants while keeping the tank clean, a true symbiotic solution.

In an aquaponic system excretions from the fish and or other aquatic animals is recirculated into a hydroponic system where it is transformed by Nitrifying Bacteria into useful plant nutrients – nitrates. Nitrates are used by the plants and purified water is then recirculated back to the fish tank.

Any Aquaponic system consists of two primary parts, the AQUA element being the fish tank or pond in which aquatic animals are raised and the hydroPONIC facet being the garden or hydroponic setup in which the plants are raised. Both the aqua and ponic elements are then grouped into their respective subsystems which handle various facets of the combined systems functions.

Aqua System Components

Rearing tank is the fishtank, tanks or pond for raising and feeding the fish

Biofilter: is a location where the Nitrifying bacteria are nurtured. These bacteria convert ammonia into nitrates, which are used as nutrient by the plants. Biofilters are not absolutely necessary in all systems and many function just fine without them so long as all other facets along the chain from fish food used to fish tank populations are kept in synch. Even though the biofilter under some circumstances is not necessary – the bacteria ARE needed.

Setting basin is used for catching assorted waste such as uneaten food and screening out fine particulates.

The Hydroponic System

The Hydroponic System is the section of the Aquaponic setup where plants are reared by absorbing nutrients from the water. It consists of ….

The Sump, which is the lowest point in the system. It is where the water flows to the plants. After flowing to the plants a recirculating system will route the water back to the fish tank while a decoupled system will not. A decoupled system allows for treatment of the plants, either for pests and disease or additional nutrient requirements as needed without risk to the fish. The more sophisticated an Aquaponic system becomes the more biofiltration becomes necessary.

Recirculating and Decoupled aquaponic systems

Aquaponic Grow Beds are where the plants grow. They vary depending on the system being used – Deep Water Culture, Nutrient film technique and so forth. If you are a novice it is not necessary that you learn all these terms right away. The grow beds are populated with a grow media or subtrate in which the plants are supported and through which the water flows over or under.

Live Components of an Aquaponic System

Live components are the fish, plants and nitryfying bacteria. If you are delving into a Vermiponics, worms are also incorporated into the fold.


The most successful plants produced aquaponically are green leafy vegetables and herbs. They generally have lower and less tedious nutrient requirements. Lettuce, spinach, basil, watercress, bok choy, coriander, mint, parsley, lemongrass are all good candidates for an aquaponic scenario.

Fruit bearing plants such as solanaceous crops [tomato, pepper, eggplant] and fruits and berries will not fare well in small aquaponic setups as small fish populations will not produce adequate waste to meet their needs. What nutrients they do provide will be high in nitrogen which is good for lush green growth but in excess is not good for fruit production. They are best grown aquaponiocally using a decoupled setup where additional nutrients can be added without risk to the fish.

Some smaller root crops such as small onions and leeks as well as radishes are also suitable for aquaponics using either a recirculating or decoupled system.


Saltwater fish are not the best for aquaponic gardens. They can be used but “saltwater” aquaponics involves a completely different set of variables. Freshwater fish and assorted aquatic animals are most commonly used.

Commercially, tilapia are frequently used, they themselves are ediible fish and using them produces not only edible produce from the plants but an edible fish harvest as well. Other edible fish commonly used are various species of catfish, blue gills and sunfish, barramundi, various species of perch, trout and bass. Any freshwater fish that can tolerate over crowding is suitable for an aquaponic setup that seeks to produce a fish and vegetable crop.

Koi which are edible but rarely eaten except as gefilte fish are suitable. Although not truely edible by most they do produce a cash crop as they are marketable live. Fish that are not commonly eaten are used as well – I have a small setup populated with guppies – although they are tiny, they reproduce prolifically and will tolerate crowded tanks. Goldfish and tropical fish used either for decorative purposes or being raised for resale will also suffice so long as they are tolerable of a crowded tank.


The bacteria are the most vital aspect of an aquaponic setup. They reduce the water toxicity by converting ammonia into nitrates and nitrites allowing the fish to survive and producing food for the plants.

Fish excrete ammonia not only via their poop but via their respiratory process and as a byproduct of their metabolism. It must be filtered out, as elevated ammonia levels will kill off the fish. Plants will absorb some of the ammonia and it is beneficial in the correct dosage but they metabolize nitrates more readily.

Nitrifying bacteria are sometimes referred to as Positive Bacteria as they have additional functions, all beneficial to the aquaponic system. One of their additional functions is in regulating the influx of harmful bacteria. A site already occupied by one form of bacteria – in this case the nitrifying bacteria will prevent other bacteria from becoming established.

Positive aquaponic bacteria / nitrifying bacteria is sold commercially under various trade names. See: Aquaponic Bacteria