The carp have arrived, and seem to be enjoying their new home. It was slightly surreal coming home to a box of live fish, but after a gentle introduction to our tanks they all swam off happily, showing no ill effects.

We got a couple of kilos of carp food delivered with the fish, but as they’re far more omnivorous than the trout we’re keen to try something a bit more home-grown.

Some of our sumps are doing well at growing duckweed so I thought that would be a good start and added a net-full of duckweed to their tank.

They’re much gentler feeders than the trout, so I haven’t seen them aggressively attacking clumps of weed, but it is steadily disappearing.

At this stage, with tiny digestive systems, they need to be able to “graze” through the day, and I think the duckweed helps with that between their main feedtimes.

As they grow we’ll try to expand their diet further to see if we can eventually produce all their feed in-house – ideally from waste, or areas we’re not using for our food.

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At some point I’ll manage to document the roller-coaster ride that was our first go at Aquaponics. Suffice to say it was a mixed success – we got to eat lots of delicious trout, but lost quite a few on the way too.

After a major redesign to get the fish out
of the polytunnel we are finally ready to go again – the system has been split to allow for different sizes, and different species, so we’re now eagerly awaiting our first Carp delivery ….

In designing an aquaponics system for your garden there are a few basic guidelines that seem to work. They cover things like the amount of fish you can stock, and the relative size of your tank and growbeds. Here are some of the main points:

  • Ideal depth of the gravel in a gravel-filled growbed is 300mm – this allows for the best conditions for plant and bacteria growth.
  • Use a 5-10mm particle size gravel for the best surface area for bacterial growth – smoother gravel makes for easier planting.
  • Maximum advisable stocking level is 6kg of fish per 100 litres.
  • Growbed volume should be twice the volume of the fish tank.

That should be enough to get me started on my basic design!

Aquaponics is the combination of Aquaculture (keeping fish in tanks) and Hydroponics (growing plants without soil). It aims to solve the problems of both of these methods, delivering a system requiring very little water or added fertilisers.

A working aquaponics system needs three things: fish, plants, and beneficial bacteria. Working together, in balance, these power a successful aquaponic system. In a typical setup, ammonia-rich water from the fish tank passes into gravel growbeds colonised by the bacteria; the bacteria convert the ammonia first to nitrites and then to nitrates, which are then the perfect fertiliser for plants to grow in the growbeds; the cleaned water then returns to happy fish in the fish tank.

Why bother? There are lots of reasons:

  • Plants in an established aquaponics system tend to grow up to 3 times faster than in a traditional garden.
  • Very little ongoing water is required – great in a drought.
  • The plants require no extra fertilisers.
  • You get delicious fish to accompany your fresh garden vegetables!
  • You can have an aquaponics system in your own back garden.

In a world where our food is becoming increasingly expensive, and with the effects of Peak Oil due to make food availability even more critical, an Aquaponic system in your back garden could make a real difference to your diet and expenses!