Greenbackyard

We have now refreshed the water in the system and getting ready for the fish. Even though we haven’t yet received the bacteria to inoculate the system, I think we should get some fingerlings to start producing some ammonia.

The tricky part so far has been trying to figure out the ratio of fish to liters of water and we’ve read multiple suggestions, posted on the Backyard Aquaponics forum, etc. We came to the conclusion that we should start with a small quantity (in order to minimise the chances of things going wrong) of Silver Perch fingerlings, maybe around 11. How did we get to that? Well, from what we’ve read there are two ways to size your fish stock. The first one depends on the mass of the fish, i.e. how many kilograms per liters you can sustain and the other one, how many liters of water you need to support a certain amount of fish. The first method says (according to what we’ve read) that you can have around 3 kg of fish per 100 liters of water, since the Silver Perch will grow to be around 0.8 kg and we have 500 liter of water, then that turns out to be around 18 fish.

According to the second method, you need to have 4.5 liters of water per 13 mm of fish and since we have 500 liter (we used roughly 450 to make the calculations easier, after all it’s a weekend), that means we could have 1,300 mm of fish, at 40 mm per fingerling, that’s around 30 fingerlings.

All these are all calculations for a well balanced system, with a lot more grow beds to water ratio … so we decided to go on the low side. We can always add more as we go.

The risk of killing the fish is too high to make the most basic mistakes. We want to be a bit more careful. We will now add 10 or 11 of these fingerlings and monitor the system to see how we go. I am looking forward to see the system in a more natural state, not with the nutrients coming from SEASOL.

So while we’re waiting for our bacteria to arrive, there are a few other things that we’re keen to sort out with our home aquaponics system! We’ve got a 400 - 500 litre tank of food grade plastic full of water, and three gravel bedsof about 60L each stacked on milkcrates right next to the tank. The water is running smoothly from the tank into the gravel beds, and draining away quite nicely. In the beds we have some small seedlings growing - they aren’t in full sunlight though and could probably do with a few more good Bondi rays.   We have no fish in the tank - we do have Seasol, a liquid seaweed concentrate in the water though, to help our fledgling plants along.

The gravel beds are about 30cm deep and their total volume is around 180L Here is a picture of our small aquaponics system. We actaully have three grow beds now. (Don’t know what aquaponics is? Head over here for a quick explanation.)

What we need to do is figure out the ratio of water to gravel beds - Bruno suspects that we are going to need more grow beds for this amount of water. And the amount of water that we need will also tell us how many fish we can have, (which will in turn effect how many plants we should aim to grow to keep the system thriving.) The plan is to buy some perch fingerlings because we’ve heard that they are pretty hardy little things, and ofcourse we have to figure out how big the fish are going to get. In this excellent forum post from backyard aquaponics forum derekh talks about a 2:1 grow bed to tank volume ratio is roughly the ideal. So as we have 3 grow beds with a volume of 180L approximately and a tank of volume 450L (or so), it would seem we need more grow beds! I’m going to head over the forums and see what they think.

This is a photo of the leaves on our cumquat tree here in Sydney. It has thrived in a large stone pot for many years, but now the leaves are going this mottled yellow colour - green in the veins, bright yellow all around the leaves. Last year we got a bumper crop of cumquats - I made a delicious jam from them, and I’d like to think I could do so again this year. So taking care of this great little tree is important to me. I put in some citrus fertilizer earlier this season (Spring in Australia) so thats a good start. I’ve heard that these symptoms could mean a lack of magnesium, or a lack of zinc, so I’m going to head over to two of my favourite forums and ask them for some advice.

What is the first thing we need to do to get our newly installed aquaponics systems working beautifully? Well you might think that once you have all the essentials in – such as the tank itself, the beds, and the plants in place, its time for something fun – the fish! But, looks may be deceiving, and as much as we are itching to get some fishies, we can’t rush into this right away. The whole system will have to be finely tuned – the plants will need to be able to adequately clean the water for the fish, and use the fish detritus as food. To do this they will need to call on the help of some bacteria, which will grow deep in the gravel, to break down the fish poo. Right now, we need to let that bacteria grow, so the system has a ‘break-in’ period of a few weeks, where we just let the water cycle through the beds.

Currently the water is a deeply unappetizing colour – brown. This is from the Seasol we have put in it – it’s a seaweed concentrate that should give our plants enough nutrients to survive in the absence of the ‘real’ food that will eventually be supplied by the fish. The whole system doesn’t smell bad, it only looks a bit iffy. And the plants do seem to be responding to the Seasol – albeit they are only seedlings right now.