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Tuesday, July 28, 2009

Aquaponics in Fishponds on Floating Rafts

After hearing about Aquaponics, many people have the throught of growing plants on floating rafts in their existing fishpond. Sounds like a great idea - fish poo, plants take up nutrients and grow. Sounds simple, but does it work?

Cris Gaston at the BYAP forums (nickname is crisgaston) recently did an experiement in the Philippines - over there there are many fish enclosures and the thought was to find out the cheapest way to be able to get a second crop for the fish farmers. If it was possible with minimal expense to grow plants in the fishponds, then this would create another income for the fish farmers and at the same time create a cleaner environment for the fish.

For the experiment, lettuce would be grown in floating ratfs directly in the fishponds. At the same time, lettuce in floating rafts would be grown in a traditional RAS raft system (RAS - Recirculating Aquaculture System). This would allow a comparision between the two.

Here is a picture of what the lettuce looked like after 35 days. Very stunted growth and only a 50% survival rate.
Lets compare this with a picture that shows the RAS floating raft lettuce after 35 days. In the bottom left corner are are lettuce that were directly in the fishpond and the rest is from the RAS system. As you can clearly see, there is no comparision between the two.
Why these results? What went wrong with the floating raft in the fishpond?

To answer this, lets look under the floating raft at the roots.
The roots show the causes of the problem. The roots show signs of root rot and are covered in a dark muck that coats them. If you were to take a hose and wash the roots down, you will see that there are white roots there (which is what you should be seeing). Instead, the roots are dirty.

Why are the roots dirty?

In a fishpond (or fishtank, any body of water you have fish in) you will get solids (fish poo) floating around in the water. These solids have accumulated on the roots of the lettuce. This accumulation of solids leads to a number of problems for the plant -

It virtually creates a "barrier" between the root and the water. This prevents the plant from uptaking oxygen and minerals from the water. This will lead to root rot a cause nutrient deficiences in the plant and hence stunted growth - this is very obvious in the above photo.

There are some aquatic plants that grow happily in an environment where the water contains solids - but you will not be able to grow vegetables this way due to the solids build up on the roots.

How do you remove the solids from the water?

There are a number of ways to remove solids from water. Before we look at that, lets look at a simplified version of a DWC (Deep Water Culture) Aquaponics system
  • Fish tank -> Solids removal -> Biofilter -> Raft
Compare this to the expierment from above:
  • Raft sits in the fishtank
There are 3 new steps introduced

Solids removal

There are many ways to achive this - in most backyard Aquaponic systems gravel, expanded clay or a dedicated solids removal device (like a swirl filter) is used. There is a catch to solids removal - you don't want to remove the solids - as they need to go through a process of mineralisation. Mineralisation unlocks the minerals in the solids into the water to make the minerals available to the plants. Gravel does this by catching the solids and giving it time to slow breakdown and mineralise into the water.


The biofilter provides a space for good bacteria to grow that converts the fish waste (ammonia) into nitrates (nitrogen) that the plants can then easily uptake and use to grow. In most backyard system, a gravel growbed is used to grow the plants - this growbed provides 2 functions - both solids removal AND biofiltration. In a raft system, the underside of the raft also acts as a biofilter!


The raft sits in a water channel which is separate to the fishpond. So the water was flowed through the solids filter and biofilter before getting to where the plants sit in the raft. This ensures that no solids will build up on the roots and that the plants have plenty of access to the nitrates and minerals they need for healthy growth.

In a raft system, the underside of the raft will also act as a biofilter. The University of the Virgin Islands (UVI) uses a ratio of 60 to 100 g of fish feed/m2 of plant growing area per day. As you can see, the more you feed your fish, the larger the plant growing area (ie raft) has to be to handle the biofiltration. If you don't have enough planting area then you may need a separate biofilter to handle the load from the fish.

If you do not have enough biofiltration, then your fish will suffer with a toxic build up of ammonia.

Images: Thanks to Cris Gaston for doing this experiment and allowing me to use the images. You can read more on the discussion of the results of this experiment here.

Saturday, July 11, 2009

Aquaponics Fish Tank - Building the base

Today I spent the day creating a base for my 1200L fibreglass fishtank. The fishtank is one of Murray Hallams designs from Aquaponics Made Easy. The base needed measures 1.2m x 1m in size and will fit nicely around the back of my garage. I have space there for 2 of the fish tanks so one day I am sure I will get another one! The base is really important to get right and level and in this case I will be making the base out of blocks and sitting on top of the blocks will be 70mm thick sleepers.

First thing I did was clear the existing pebbles that are in the ground and excavate about 10mm. The blocks themselves will be sitting on a base of crusher dust. Crusher dust is excellent because it is cheap, easy to get anywhere and compacts down. So you can easily spread it, them wack it down with something heavy like a piece of wood to compact it, and then place the block on top.

I made my measurements out from the garage wall as I wanted the tank to run parallel to the wall and quite close to it. So I made the measurements and hammered some steaks into place then attached a string line. You can see that the steaks are placed past the corners. This means that where the string lines intersect gives you your corner.

After placing the first block, you can then get a height for the top of the stringline. This allows you to easily set the height for all of the future blocks. You can see in one of the pictures a level that you attach to the string line that allows you to get the stringline level. Make sure that you make the stringline really tight!

I was constantly checking the levels! I found a mallet useful to make minor adjustments and my foot to make sightly larger ones - like if I had to make one end lower I would wack it with my foot.

Once I got a block level, I would then check it against another block by making the level go across both blocks. Sometimes I had to make a few minor adjustments, but most of the time I could get the heights correct thanks to the stringline.

If your blocks are level then placing the sleepers on the blocks, the sleepers should be level as well. So if you place a sleeper on and then the level shows an issue, then there may be an issue with the sleeper. It may be bowed or different thicknesses at each end.

These sleepers are 70mm thick hardwood. They come in 2.4m lengths, so cutting one in half would give me the 1.2m length I need. The first one I cut had one end which was less then 70mm thick. I didn't notice this until I placed the sleeper which went width ways. When I did that, it was then I noticed the difference in height between the two sleepers. This is something to be wary of with hardwood sleepers as they are only rough cut and may have issues like this.

After I was happy that all of the blocks were fine and the sleepers were all good, I then raked the pebbles up against the blocks so that they covered the crusher dust and gave a little support to keeping the blocks in place. After the tank is filled, there will be over a ton of weight pushing down, so those blocks wont be moving anywhere!

So that's it for the fishtank base. I hope this has been useful and if you have any questions, ask away.

Tuesday, July 7, 2009

The BioPod - Black Soldier Fly Larvae Harvester

This article will take you for an in depth look at the BioPod and talk more about the Black Soldier Fly - which I will call BSF for short. We are not so interested in the fly itself but in the grub - as that can be used for feeding your fish in an Aquaponics system.

The BioPods purpose is to produce the grubs which are a result of the 6th stage of pupation. This final stage is before it morphs into a fly.

The BSF larvae I'll sometimes refer to as grubs. They are often called phoenix worms or soldier grubs and are often sold live in pet food stores.

The adult BSF look less like flies and more like wasps. The BSF does not have any mouth parts, hence it won't be a problem around food and won't transmit disease.

In a typical worm farm or compost there are a variety of meats and foods that you would never put in there. But not for the BioPod - you can throw it all in, even animal manure, they love it and will consume it quickly.

The BioPod creates an ideal environment for the grubs and best of all they will harvest themselves conviently into a bucket when they have reached their final stage of pupation.

This gives you a system that very efficiently recycles wastes and in the process creates an excellent food source for a variety of animals.

Uses for the grubs

There are many many uses for the grubs. One of those is for feeding fish. In Aquaculture and Aquaponics, the grub is increasingly being used as a food source in order to reduce the use of fish pellets. It is also quite nutritional, being very high in protein. Other uses include feeding birds, repitles, chickens and a range of other animals.

Path of the grub through the BioPod

Here is a quick fly-thru of BioPod. After the larvae has gone through its 6th stage of pupation and no longer has a mouth, it will make its way up the 35 degree ramp.

Once it reaches the top, it will nosedive down the hole and end up in the collection bucket - ready for you to harvest it!

Storing the grubs for later use

During the warmer months you will get a much larger production and hence need to feed them more. If you have more then you need on any given day, then simply freeze them for the colder months when production isn't as prolific. By freezing them, you can have a plentiful supply all year round.

The liquid tea

Here is the filter located in the centre bottom inside the BioPod. The liquid flows out of the hole, through the filter and into the container underneath. The liquid can actually be used as a fly repellent for other flies except BSF which it will attract. This is the container which is removable by twisting it off. You can also use the liquid as a plant fertilizer.

In the removable cap that sits on the top of the BioPod is a gap that allows the BSF easy access into the BioPod. The BSF secreet a fly repellent for all other species of flys, so you shouldn't have to worry about filthy flys getting into your BioPod when you have BSF in there.

The BSF adult wont eat anything, as it doesnt have a mouth. Its only purpose as an adult is to mate and lay its eggs. The eggs hatch about 5-8 days later. The lifespan of the adult is very short, only about a week.

The BSF 5-star hotel

Your now looking under the cap.

The adult likes to lay its eggs either above or next to a food source. Under the cap you will see a white disc shapped object. This disc is the ideal place where adults will lay their eggs. The eggs will take about 4 days to hatch. When they hatch, they will fall into the food and start munching away.

Commercial BSF production and further info

If you want to produce grubs on a large scale, then there are commercial versions available. Today we have had a look at the residential version. The official website for the BioPod can be found at At the site you will also find a forum where you can get all of your BSF and BioPod questions answered.

Images - The Black Soldier Fly image is from Muhammad Mahdi Karim and the picture of the grubs is from