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.