Aquaponics Garden Part 5 – The tiny critters that make it all work

I’ve been saying that the aquaponics garden works because the plants use fish waste water as fertilizer and while that’s true, it is, like many things, a gross simplification. Fish poo and pee and also excrete ammonia directly through their gills. Not only is ammonia toxic to fish, but plants cannot actually use these things either. Luckily there are bacteria everywhere that will convert the ammonia to nitrates which plants do use. These bacteria may be everywhere, but it takes time before a sufficiently robust colony of them is established in an aquaponics system (or aquarium) so that a full stocking level of fish can be safely kept. The process of establishing this colony is called cycling.

Cycling can be done with fish in the tank or without, but I have chosen to cycle with a small number of fish. Madeleine has a healthy, fully cycled aquarium and she gave me some well used filter floss from her filter to jump start the cycling process. This stuff is loaded with the nitrifying bacteria that will colonize the grow media with its huge surface area and ultimately every surface in my system. I buried them in the grow media just under the water inlets of the grow beds. Nitrifying bacteria are pretty slow growing in bacterial terms, doubling in about 15 hours more or less, depending on temperature. The four small goldfish will hopefully provide enough ammonia to keep the bacteria fed while they are growing.

I’m doing daily water tests to determine whether the system is cycled yet or not. It can take up to six weeks to cycle from scratch. So far, I have not detected any nitrites or nitrates, and only barely detectable levels of ammonia. Since there will be a period of time before nitrates appear, I have added liquid seaweed to the system to provide nutrients to the plants, and a small amount of ammonia for the nitrifying bacteria. I’ve been heating the water in the tank to 23C, for the benefit of the bacteria, though the fish and plants are fine with it, too. Goldfish are able to tolerate a wide range of temperatures, a real advantage in terms of fish suitability for an aquaponic system, but for now they get to enjoy the warm bacteria-growing water.

Getting the system cycled is my immediate goal as it is the key to happy fish and plants. As an aquaponics gardener I am basically a bacteria farmer. If I can keep the bacteria happy, everything else should fall in place.


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