I'm making a tiny aquaponic system in my cellar - it's my first attempt at anything like this so I could do with some advice!
I'll be attempting to grow Head Lettuce (keeping it simple first) in a Lava Rock grow bed medium, with a yet to be defined number of goldfish (not attempting to raise fish for food this time) in approximately 20 liters of water in a tank below the grow bed. The water will be cycled via a pump, using the ebb and flow method.
I want to get the fish in and happy, then introduce plants. I've still got to decide on the best way to do this from a beginners point of view.
The fish tank is an A3 plastic storage box, filled with around 20 liters of water. There is a 5W 600l/h pump on a timer in the corner of the tank, directly below the grow bed. The pump lifts around 1 liter every 10 seconds. It takes around 2 minutes for the grow bed to be filled to the level I want, and a further 2 minutes for it to drain. This will happen 4 times an hour, which should move nearly 50 litres of water through the grow bed every hour - I read you should completely cycle the water at least once an hour, anything more is a bonus.
The grow box is an A4 plastic storage box, filled with approximately 19cm (7.5") of Lava Rock as the medium. The grow box will fill to around 14cm (5.5"), leaving a dry top layer - I've read somewhere this helps prevent mould. I spent about an hour rinsing the Lava Rock out - a trial run left me with cloudy red water in the fish tank.
I didn't think about how much weight the grow box, medium and water would be combined - I think I will get a hold of a plank of wood to sit it on, instead of balancing it on the bigger box below. The A3 box sags a little when the water reaches its peak in the grow bed. It feels stable enough, but I don't want to take the chance of some kind of structural implosion
I employed a high tech drainage system: drilled a load of holes in one side of the grow bed box, right at the bottom. I never really thought this one through - got a bit drill happy. The end result was a system that seemed to drain water faster than the pump could put it in, so I had to cover some of the holes with tape. This grow box has taken a bit of a battering in the 'prototyping' process, so I'll probably end up getting a new one before I introduce the plants.
All that's left now is a bit more research on how many fish I'll need, and how to introduce the plants. There are some pictures of the setup on my blog - if you can see anything that's going to cause this to fail, please let me know in the comments - any feedback would be hugely appreciated
Sorry to burst your bubble but small aquaponic systems are inherently unstable. You have to watch the water chemistry every day or you'll kill all your fish. You can have a very low fish stocking density, but they you won't grow much plants. Most aquapons agree that you need 200 galllons, minimum.
You probably want a way to flood the bed all the way to the top and then drain it. You could use a bell siphon. Your system is a bit like My Aqua Farm, so you might could learn something from their designs.