From July, 2013

Stage 3: The Cycle of Life

We’ve spent the past few weeks cycling our system to build up a biofilter. The biofilter is the key to a successful aquaponics ecosystem – it’s the bacteria that turns the fish poo into fertiliser for the plants. The fish produce waste in the form of ammonium, which is then converted by the bacteria nitrosomonas into nitrites. The nitrites are converted by nitrospira into nitrates, which provides a delicious and nutritious meal for the plants.

The cycling sounded fairly straightfoward:

Step 1: Add ammonia

Step 2: Stuff happens

Step 3: Success!

But it’s proving a bit more tricky than anticipated. First we tried to cycle the system using ammonium chloride, which is a powdered form of ammonia. The advantage of this method is that there are no fish or plants at the mercy of volatile bacteria colonies. However, as we cycled over a few weeks the bacteria colonies never really seemed to settle in, and recently seemed to have left us altogether.

So I decided to go for a more hands-on technique – cycling with the first few intrepid fish. Cycling with fish means you don’t have to introduce any outside chemicals into the system, as the fish produce the ammonia themselves. It means you have to keep a closer eye on the system though, to avoid fish martyrs. When I showed up at the shop today though, the system was looking pretty grim – an algal bloom had struck!

Tanked tank

I reckon it was a bit of a viscous cycle: the algae clogged up the pipes, cutting down water flow and leaving conditions better for more algae to grow, which completely stopped the taps this afternoon. The tank is also getting a lot of light where it is, so we’re going to cover up the window-facing side to cut down on sun and give the fish some privacy.

The fish had only been put in this morning, but there was no way they could stay in there. It certainly wouldn’t start things out on the right foot/fin.


We got them into a temporary abode, changed the water, and cleaned the algae off. The water can sit over night to let the chlorine evaporate (Glasgow’s tap water is actually quite good pH-wise and there isn’t much chlorine in it, but it will still have a bit) before reintroducing the fish to their home. For a more in-depth explanation of the cycling process, check out

ImageHere’s the system, sans fish. That trooper of a tomato plant has been there since the beginning. Looking a bit yellow at the moment without any nitrates, but still throwing out a few flowers. Can’t wait to see it flourishing in a few weeks!