Our Aquaponics System

Triple grow bed aquaponics system, with pak choi, cabbage and lettuce seedlings, and 17 tilapia fish

Triple grow bed aquaponics system, with pak choi, cabbage and lettuce seedlings, and 17 tilapia fish

Following on from our last post detailing HOW TO BUILD A SIMPLE AQUAPONICS SYSTEM we thought we would share our current set-up, which offers some variations on the simple build. The main difference is the expansion into 3 grow beds, and a large cylindrical tank which is currently home to 17 tilapia. Cylindrical tanks are a great choice as they have fewer ‘dead spots’ than rectangular ones, so the water flows around the full surface of the tank.

Pak choi seedlings, planted in bottomless pots for easy transferal and greater stability. White mineral deposits on pebbles (have recently appeared but do no harm).

Pak choi seedlings, planted in bottomless pots for easy transferal and greater stability. There are white mineral deposits on the pebbles which have recently appeared but do no harm.

We are planning on adding some new beds (possibly in tower shapes, with the water trickling from top to bottom) in the next few weeks, as we have adequate nutrients to support these and this will only increase as the fish get bigger! They are currently between 2 and 3 inches and have grown about an inch in the last 3 weeks.

Hope you enjoy looking at our system images (full layout diagram below – click to enlarge) and that they give you some inspiration for your own set-ups ☺︎

Our System Diagram COLOUR

How To Build A Simple Aquaponics System

Full Diagram

A Basic Guide To Building Your Own Aquaponics System (Click Image To Enlarge)

Aquaponics is a technique enabling the sustainable production of edible fish and plants in a re-circulating system. Fish waste acts as a natural fertiliser, the plants absorb these nutrients, and the water remains clean and stable for fish. The only input is food for the fish.

Water from the fish tank is pumped into the grow beds and solid waste is removed by the addition of filter media at the water exit points. The water then travels through the plant grow beds where plants uptake the nutrients, and the water returns, purified, to the fish tank. The grow beds become a natural biofilter for bacteria to convert fish waste into accessible nutrients for plants.

The Biological Components of Aquaponics: The Nitrification Process (See Top Diagram)

The process of nitrification prevents the water from becoming toxic with harmful forms of nitrogen (ammonia and nitrite), and allows the fish, plants, and bacteria to thrive symbiotically. In a properly balanced system, all the organisms work together to create a healthy growing environment for one another, and form this cycle:

Food is eaten by fish > Fish produce ammonia in waste > Bacteria breaks down ammonia into nitrite > Bacteria breaks down ammonia into nitrate > Nitrate is taken up by plants for growth > Water is left clean for fish

What You Need To Build Your System

Basic Structure

Tank for fish (made of strong inert plastic)
Tubs for Grow Beds (at least 25cm depth)
Modified Table / Frame to support Grow Beds
Inert growing media (we recommended expanded clay pebbles 8 – 20mm in diameter)

Plumbing Components

¾ inch PVC piping
Large PVC pipe for gravel guards (3 – 4 inch diameter)
¾ inch hosepipe
Hose cap
Tank connector
Female tap connector
¾ inch rubber O rings
¾ L bends


Submersible water pump (flow rate depends on size of your tank)
Tank heater (dependant on fish)
Air pump, air stones and air line
Grow lights (if growing without natural light)
Plugs Timers (to regulate pump and lights)


¾ inch hole saw attachment
3 – 5mm drill attachment (for water exit points in hose)

Master water test kit
Solid Waste Filter Media (this is too remove any solid fish waste so it does not clog the system)
Ammonia Source
Water de-chlorinator
Seeds (leaf salad, lettuce, spinach, pak choi, cabbage and herbs are good plants to start out with)


The Build (Click Image To Enlarge)

All aquaponic systems share several common and essential components. These include: a fish tank, a grow bed, plumbing, and electronics, all of which need to be in a structurally sound before any growing begins. There are many ways to build an aquaponic set up depending on the materials you have available. This is one suggestion and can be adapted to suit your needs. (N.B. In this set-up, the tank connector is situated directly over the fish tank, so you may not need the female connector and extra PVC pipe. Use these elements if the grow bed is much higher than the tank, or you have multiple grow beds and are using extra piping to redirect water back to the tank.)

  1. Situate the fish tank underneath the grow bed(s). The easiest way to do this is by modifying a table, constructing a frame or using breeze blocks or bricks for supports.
  2. Once you have decided where the grow beds will be in relation to the fish tank it is time to fit the plumbing. Using a ¾ inch hole saw, drill a hole in the centre of the bottom of the grow bed.
  3. Position an O Ring on either side of hole and place the tank connector through the grow bed. Adding some marine safe sealant at the join can help in achieving a watertight seal.
  4. To create the stand pipe, cut a piece of PVC pipe, so the length is 2 – 3 inches below the top of the grow bed, and drill a drainage hole near one end, making sure it is not blocked by the base of the tank connector when inserted.
  5. Screw the female connector to the thread of the tank connector underneath the grow bed and arrange pipes using relevant connectors so the water will drop directly into the fish tank. (N.B. Repeat steps 2 – 5 if using more than one grow bed.)
  6. Cut the wider PVC pipe taller than the grow bed to act as a gravel guard, and drill three rows of evenly spaced holes around the bottom of the guard to allow water but not grow media in. Place guard over stand pipe and use sealant to secure.
  7. Fit the hose to the water pump and place it in the fish tank. Cut the hose to size so it reaches the grow bed, if constructing a system with more than one grow bed, the hose must be long enough to pass through all of the beds.
  8. Before fixing the hose to the grow bed check the system for any leaks. Partially fill the bottom tank and switch the water pump on. As water fills the grow bed it should drain back into the tank through the standpipe. Once the pump is switched off, water should drain slowly away through the small drainage hole in the stand pipe. If there are leaks drain the system and seal with marine safe sealant. Allow it to dry and check the system again.
  9. Fix the hose to the grow bed by drilling another two ¾” holes in a way that allows the hose to run along one side of the grow bed just beneath the top. Drill 3 – 5 evenly spaced 3mm holes in the hose to allow the water to enter the grow bed, and secure hose in place. Fit and seal a hose cap to the open end of the hose. Check the system plumbing again.
  10. Once the mechanics are working and everything is properly sealed, thoroughly rinse your grow media to wash away any excess sediment. Fill grow beds to just underneath your hose with grow media. Put some solid waste filter media underneath the water exit holes in the hose to filter out any solid fish waste, so that it does not enter the grow bed. (This can be rinsed with water every few weeks when waste starts to build up.)
  11. Connect the air stone, air line and air pump. Drop the air stone into the tank, keeping the air pump above the water level. The air pump can be attached to the frame.
  12. Fill the tank with de-chlorinated water. It may be easier to fill the tank through the grow beds if access to the tank is awkward or limited. Switch on the air pump and heater.
  13. The system is now ready for fishless cycling and water testing.
  14. Run the water pump continuously through the cycling period, it can then be regulated using a plug timer as required depending on your plants. Having the pump on for 15 minutes every hour is usually sufficient and gives enough time for the water to drain completely from the grow bed allowing oxygen to the plants roots. When the roots develop, the stand pipe can be cut down so the bed does not flood as high.

Notes On Water

Water is the life-blood of an aquaponic system and is important to get right. It is fine to use tap water although it is treated with chlorine and chloramines among other chemicals to make it safe to drink. These chemicals are toxic to fish and the water needs to be dechlorinated either by storing the water and allowing the chlorine to evaporate naturally (24 hours) or adding a water dechlorinator (immediate).

Hope these instructions are useful! We are currently producing a quick-guide publication on Aquaponics, so any feedback is very helpful. Happy Building!

Tilapia Care in Aquaponics


Tilapia were our fish of choice for our larger aquaponic system. Not only do they taste good they are pretty easy to look after and are a hardy fish that can withstand a drop in ideal water parameters. Before keeping them however, there are some important basics to get to know.

Temperature: Tilapia require heated water, especially here in the UK! 28°C is the ideal temperature and this can be achieved with an ordinary aquarium heater that is the right size for your tank. A few degrees either way probably won’t make much difference but they definitely cannot stand extended periods of colder water.

Oxygen: Water dropping from the grow bed into the fish tank will agitate the water surface and allow for an exchange of gases, oxygenating the water. It is a good idea to add an extra air stone incase your system is on a timer and the water goes still for long period of time. If you spot any fish gasping at the surface definitely try adding another air stone. Tilapia also use oxygen to metabolise their food making the need for an air pump even more important.

Feeding: It’s always best to get a good quality feed especially made for tilapia. It’s also possible to feed them directly from your system, or incorporate growing something like duckweed that be fed straight to the fish. Tilapia can be mostly vegetarian although in their earlier development they need a lot more protein. Feeding smaller amounts spread throughout the day will be easier on the system and more regular for the fish. We are using an automatic feeder for when we aren’t around to make sure they get their feed. We are feeding 3 to 4 times per day and only what they can eat in a few minutes, if there is food being left by the fish cut back on the food per feeding. Amount of food to be given will change as the tilapia grow, it’s important not to underfeed them!

Stocking Density: Without going into specifics of gram per cubic foot, a general answer is one adult tilapia per 10 litres. We have taken this rule as the absolute maximum and have stocked under this amount.

Water Parameters: While I mentioned tilapia being a hardy fish this is no excuse to keep slack water parameters! It just means if there is a slip up or a pump stops working there is some leeway to fixing to problem. Ammonia and nitrite should be at 0 ppm to keep the fish in optimum health. Nitrate should be kept under control with regular testing to make sure the plants are doing their job and taking this from the water.

Sourcing: Our tilapia have come from Fish Farm UK based in Bow. They deliver to other places in the UK and we highly recommend them. Most sizes are available at a reasonable rate and they care about their fish! A quick online search will provide other suppliers.


Starting Your Seedlings In Clay Pebbles

Photo 01-09-2014 10 03 20 am

There wasn’t much about the success rate of starting off seedlings in clay pebbles in any of the aquaponics resources I researched, but I thought I would give it a go as transplanting a clay pebble pot straight into an aquaponics grow bed is much less disruptive to the plants than washing soil off the roots and redistributing them in different media.

Whilst I was waiting for my aquaponics system to properly cycle I started off some spinach, pak choi and basil, in the same clay media as my grow bed. I also grew some seeds in soil to monitor the difference. Obviously as the soil has more nutrients after about 10 days the soil plants started to grow much faster, however once in the system the plants in the pebbles were eventually much stronger than the soil plants. I think having all the roots washed and rearranged in pebbles did not leave the plants in a happy mood and in-fact some of the wilted and perished! This did not happen with any of my pebble seedlings.

Photo 05-09-2014 03 15 03 pm

VERDICT: Start off your seedlings in the same growing media as your system. Plant them in a pot with holes in the bottom so you can pop them straight in your grow bed. Grow them for about two weeks (or until the roots poke out the pot) before putting them in the main bed, and if possible water them with the same water that is in your system BUT only if it is fully cycled.

TIP: A heated seed tray helps development and of course lots of light is beneficial. 

Fishless Cycling For Aquaponics

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Getting started with your aquaponics system is pretty straightforward once you have the know-how. We will be doing a step-by-step guide to setting up a small system soon, but first I thought it would be useful to talk about the science behind getting your system ready for fish and plants.

There are two options for cycling your system, with fish or without. Getting your system ready so that the right bacteria have established to convert the fish waste into plant food is essential before you start any growing, and to make the water safe for the fish. We think fishless cycling is much more straight forward as your are not panicking about levels of ammonia and nitrite shooting up and potentially poisoning the fish in the initial stages. The cycling process usually takes about 3 weeks.

What you are trying to establish is a natural cycle whereby all harmful substances are eradicated:


Without fish, you need a way of simulating their waste products in the system. Household ammonia is perfect for this, as fish waste is ammonia-based. You can get it from most hardware stores or cleaning supply places (I got mine from Robert Dyas). Using this method you can control the amount of ammonia in your system precisely, which is also an advantage over cycling with fish. (Some people use their urine but this is more difficult to control and potentially not that pure).

Things you need for cycling:

  1. Pure household ammonia
  2. Small pipettes for measuring amount of ammonia you dispense
  3. Test kit so you can measure levels of ammonia, nitrite and nitrate in the water, plus the PH levels. This API kit has everything you will need. 

IMPORTANT: Before you start cycling, test your water. Some tap water already has high levels of Nitrate and is not really suitable for Aquaponic systems (in this case you could collect rain water if you live somewhere with unpolluted rain, or as a last resort you might have to start off with water bought from the supermarket – you can buy 5L canisters for relatively cheap). Always let tap water rest for 24 hours so the chlorine added to UK tap water has evaporated. You can also buy Tap Water Safe products from your local pet shop to make your tap water safe. 

Once you have got your ammonia and your test kit just follow these instructions to get going:

  1. Add ammonia to the tank a few ml at a time until you reach a reading of 3-4 ppm.
  2. Record the amount of ammonia that this took (probably around 3-6ml depending on your tank size), and then add that amount every other day until the nitrite appears at about 0.5 ppm.
  3. Once nitrites appear, half the dose of ammonia or just hold off for a while if you are worried about overdosing the tank, the nitrites will probably increase for a while, do not worry about this, it is normal (mine spiked at 4ppm).
  4. Once nitrates appear at around 10 ppm, and the nitrites have dropped to zero, you can introduce your fish. Mine nitrates went a lot higher than this initally, but up to around 40 ppm is still safe for fish and this number should drop once you plants start to take up nutrients.

WARNING: Be careful with the amount of ammonia you are adding. If you are setting up a small home system DO NOT overdose the system! If this happens you will have to wash everything out and start again which is very frustrating!

This is a graph of what happened in my system, with the PH, Ammonia and Nitrites. As you can see if took a while to settle down and was quite up and down in the beginning:

Screen Shot 2015-02-01 at 19.21.45

NOTE: Your PH should stabilise over time, mine was very up and down but eventually stabilised at about 6.8. This is a good level for both fish and plants.

TIP: It is a good idea to start your seedlings off in the media you are planning to use so you can put them straight in the system once the fish are in. So start the seedlings about a week after you start cycling if you can, a heated seed bed and lots of light helps them to stay healthy. 

Below is a graph of my system also showing what happened to the Nitrates just for interest. My tap water started with around 40 ppm so this is probably not representative of what would happen in most peoples systems but thought I would include it for interest. As you can see the Nitrate increased, and then the point at which it starts to decrease is after I installed some plants.

Screen Shot 2015-02-01 at 19.36.50Happy Cycling!