Las garrapatas y otros vec- vec-tores olvidados

• Siphon standpipe (left)

• Bell siphon tube with airtight cap (centre)

• Shroud pipe (right) Installing the standpipe

Around the standpipe we need the bell siphon tube, which should be approximately 2 times the diameter of the standpipe. The bell tube needs to be sealed at one end (the top) with an airtight cap. The bottom of the bell tube needs to have some holes drilled or cut to allow

water flow. Two 25mm holes opposite each other at the bottom (open) end of the siphon bell tube should suffice. These holes allow water to flow up and into the siphon. In addition, drill one small (8mm) hole 4cm up from the base of the bell tube. This hole sets the minimum water depth in the growbed - as the water drains from the growbed, and the depth decreases sufficiently, air is sucked into this hole and breaks the siphon, causing the growbed to stop draining and to start filling up again.

This bell tube is simply lowered on top of the siphon standpipe, and stays in place by gravity.

A shroud should be placed around the bell tube. This is simply to prevent growing medium and plant roots entering and clogging the siphon and drain pipes. The shroud can be made of a wider diameter pipe (4” drainpipe) with many holes drilled in it to allow unimpeded water flow.

Repeat these steps for the other growbeds; ensure the drain of each one reaches the sump/fish tank.

Growbed supply pipes

The growbed supply pipes deliver water from the fish tank to the growbeds. As they will also carry solid waste, it is important to use wide bore pipes to prevent clogging. Remember that the growbed surface should be 15cm lower than the water surface in the fish tank, so these pipes will also need to accommodate this height difference.

Pipework

T-junctions and ball valves used to regulate the water flow to individual growbeds; 32 mm PVC pipe fittings.

Internal fish tank plumbing for a constant height system. The 50mm wall connector (right) goes through the fish tank wall at the desired surface level, and connects to the growbed supply pipes. The long standpipe under the T-junction draws water up from the bottom of the fish tank.

Detail of the holes at the bottom of the bell tube

Lowering the bell tube onto the standpipe

A final fact to consider is that the outlets to each growbed need to be perfectly level with each other. If one outlet is slightly lower than the rest, then all the water will flow through it, leaving the other growbeds dry. It is a good idea to use a ball valve on each outlet; that way it is possible to regulate the flow to each growbed and compensate for slight differences in height.

Drill a hole in the fish tank wall at the desired water surface level. Put a wall connector through this hole and use a pair of L bends on the outside to bring the pipework lower than the outlet level. The pipe should then run horizontally, with as few bends as possible, for the length of the growbeds. Each growbed is supplied via a T-junction from this pipe.

On the inside of the fish tank, attach a T-junction to the wall connector (not an L bend, or all the water will siphon from the fish tank!) with a pipe extending vertically almost to the bottom of this fish tank. This is so that the water going to the growbeds will be drawn from the bottom of the fish tank, drawing with it any solid waste. It is a good idea to screen this pipe to prevent small fish being sucked up into the plumbing. An easy way to do this is to cap the end, and drill a lot of 8mm holes in the cap and bottom few centimetres of the pipe. Pump

Make sure that the pump is the right capacity for your system – measure the total height difference from the floor of the sump tank (where the pump will sit) to the top of the fish tank (where the water will discharge). This height is the head. Now estimate the total volume of water the system will hold – this is the volume the pump should be able to move every hour. Check that your pump’s flow rate at the given head is sufficient to cycle the whole water volume every hour.

Place the pump into the sump tank and connect it to a pipe leading to the fish tank. It can be useful to put a T-junction and ball valve in this pipe to enable direct water return to the sump tank. In this way, the flow rate to the fish tank can be controlled. Again, use as wide a bore pipe as is possible, and try to avoid sharp direction changes; this helps to minimise resistance, thus increasing the pump’s efficiency and lifespan.

Pump, pipe to fish tank and ball valve for water return to sump tank. Growbed supply pipe detail

6: Fill with growing medium and water

Once the construction is finished you are ready to fill the system with growing medium and water. Whichever growing medium you choose to use, it is important to rinse it well first so as to avoid introducing fine silts to the system. Put the washed medium into the growbeds to a depth of 30cm, making sure that the siphon pipes do not get dislodged (putting a brick on top of the pipes helps). Then fill the system up with fresh water.

7: Switch on the pump

Make sure that the electric connections are located in such a way that they will not get wet, plug in the pump and switch it on.

8: Check everything

With the pump running, check the system for leaks, ensure the siphons function correctly, and adjust flow rate as necessary using the ball valves feeding the growbeds and returning to the sump/fish tank.

It is normal for the water to run a bit cloudy for the first few days – you can never rinse all the dirt from the growing medium.

9: Cycle the system

“Cycling” is the term used for getting an aquaponic system biologically ready to hold fish and plants. Please refer to chapter 2 for details.

Chapter 10:

System

operation