Nitrobacter, nitrosoma for aquarium water filtering

A normal attached media biological filter as used in an aquarium is good enough for a small set-up. For a very large one, a reinforced concrete filter as used in ornamental fish ponds will be needed. Obviously what size the filter should be will depend on the total mass of fish being kept. As a general rule of thumb, 1m² of filter media surface will remove 1 gram of NH₃ per day, while 1kg of fish will excrete 0.25g NH₃ per day. Add another 0.02g NH₃ from the fish food, and you'll get 0.27g NH₃ per kg of fish per day.

If you have a friend who has a healthy cycled fish tank, get some of the brown sludge from his filter: it's essentially a dense colony of bacteria. Another way is to put one or two slices of fish into an empty tank and let the pump circulate the water continuously through the filter. After 2 weeks to a month, the tank should have cycled. Use a nitrite/nitrate test kit to check the water NO₂ - NO₃ levels. A properly cycled tank should only show NO₃, with no detectable NO₂ or NH₃ levels.

Your process flow should look like this:

Fish tank → biofilter → plants

Note that once the plants have removed the NO₃ from the water, it is safe to return the water back to the tank. Note also that excessive NO₃ levels will eventually harm your fish. I have set up one such pilot plant and have not needed to replace the water for > 6 months. And yes, the fish is still very healthy.

I'm wondering about some of the "specs" for the simplest possible biofilter I can make and how rapidly it might be able to do the water cleaners. For instance, if I pumped the "dirty" water into a 1 quart (1 liter) container, , filled with aquarium gravel, or beach sand and let it sit for 30 minutes (or two hours?), would the bateria have enough time to operate on that amount of water before being passed by the plant roots in a hydroponic set up ? Which would be better for the bacteria or settle on, sand or gravel, or something made of a plastic, or metal ? Would a "wool", or some other fiber spun material, e.g. glass, or rockwool, be better yet ? (is it better if the water is flowing rather than sitting, and at what "speed" ? If I can get the two separate bateria, nitrosoma and nitrobacter, is it better to have each act on the dirty water separately or together ? (I'll ask my questions one (or two) at a time, to get fullest detail. Reference to some visuals would also be very appreciated.) Thanks.

1. Nitrosomonas oxidizes NH₃ to NO₂, while nitrobacter oxidizes NO₂ to NO₃, so it's better to have nitrosomonas, then nitrobacter in that order. In reality though, they'll probably be found in mixed colonies.
2. Minimum required contact time is 20 minutes as a general rule of thumb. Obviously longer is better.
3. Both nitrosomonas and nitrobacter are aerobic bacteria, so flowing water is better. Alternately, you can have standing water if it's well aerated. Note that they are facultative bacteria, so without sufficient DO, they'll breakdown the NO₃ to obtain oxygen. This by itself isn't a bad thing, except then your water will be NO₃ depleted and thus will not provide a nitrogen supply for your plants.
4. Use a medium with an extremely high specific surface area e.g. activated carbon or crushed coral to get maximum growth space for your bacteria. You can get the details from your supplier.

Email the guys at www.1aquaponics.com.au and they will give you some written plans for aquaponic aquariums. andrew