Backyard Aquaponics
A place to discuss aquaponics

I was recently approached by a passer-by who saw my complicated aquaponics system and is keen to set up a system for an orphanage in Kenya. I'm thinking that my system is overly complex (with 2 grow-beds, 4 fish tanks, a water pump, timer switch, air pump, soon to have NFT tubing, a separate water pump with particulate filter, and battery backup).

I've been thinking about an all-in-one raft system, where the fish swim around under the foam, and there is a "passive" biofilter in the tank (similar in principle to an under-gravel filter in an aquarium, although maybe oriented differently). The foam would providing thermal insulation and reduce evaporation, and there would be just a single aeration device, be it a water pump, air pump, paddle-wheel or air compressor. It would be ideal if the aeration system was sufficiently low-powered to allow the whole thing to run off a small wind turbine (or solar PV panel) and 12V battery.

The key principle is to maximise simplicity.

Any thoughts? I'm thinking that one issue may be plant roots being nibbled by fish, but this could perhaps be overcome by installing plastic mesh guards under the foam.

If this is an old idea, can someone please direct me to the appropriate thread? :-)

It may seem at first glance that a raft system would be simpler but as far as maintinance goes, I don't think you can get any simpler than flood and drain gravel beds.

The raft systems I've seen so far have the fish tank and raft tanks separated, so a water transfer is still necessary and hence there is no gain in terms of simplicity; however, the system I am proposing (though I'm sure it is not an original idea) has a single body of water and possibly just a paddle-wheel to generate circulation and aeration.

Is there some factor I'm missing somewhere? Perhaps there is an obvious reason why the single-water-body system wouldn't work...

could you just float the raft in your sump tank? it would just float up and dwnn with the water level, making sure it has lots of O2 and doesn't drop down low enough to tangle roots in the pump and what not!

Sure, this could be a good way to increase the productivity of an existing system (per surface area) and insulate / reduce evaporation, but I'm thinking of an entire stand-alone system designed specifically to have the bare minimum of moving parts. Hence the biofilter inside the fish tank, the plants floating above the fish, and a single aeration / circulation device.

The concept is similar to to Aeldric's system:
viewtopic.php?t=668

Well yeah... it is a kind of "old idea" Jimmy.... in fact it was the fore-runner to aquaponics...

New Alchemy Institute... 1976.... scroll to page 6...

http://nature.my.cape.com/greencenter/pdf/solaraqua.pdf

Or the complete read... http://www.fastonline.org/CD3WD_40/JF/J ... _farms.pdf

Also good reading...

"The Saga of the Solar-Algae Ponds" - Zweig 1977
“ Irrigation of Garden Vegetables with Fertile Fish Pond Water”. by Wm. McLarney
“ Walton Two: A Compleat Guide to Backyard Fish Farming” by Wm. McLarney & John Todd.

http://nature.my.cape.com/greencenter/list-aqua.htm

Thanks for those links! I've downloaded and will read when I'm not on work time...

Why read in YOUR time??? Very un-Australian attitude you have there:)

Hi Jimmy. IMO, the fish will most probably eat the roots of the plants. If you put some screen underneath, fine, but the fish will not be able to reach the water surface if they have to in case of low DO. Secondly, the foam cover will not allow for the transfer of oxygen from the air into the water. In my experience, water surface area and movement are key factors in maintaining good DO levels. Check my post in Members' Systems. It's a simple raft system driven by airlifts and gravity. No water pumps. Cheers.

Some things to keep in mind (sorry I have not read the articles and other things in the links posted so I may be missing some things) anyway, You might be able to grow some plants in a floating raft on a fish tank but the plants and fish are only two thirds of the Aquaponics triangle. Ya gotta remember the bacteria.

Somehow I think simply sticking a sponge in the bottom of the fish tank without any pumping does not an undergravel filter make. You need to move the water through your "filter" (most under gravel filters are not totally passive, there is usually a pump or powerhead sucking water from below the gravel) and it needs enough dissolved oxygen to support not only the plants, the fish, and the bacteria but also any other decomposing waste caught in the filter. These things all use dissolved oxygen. Now while you might be able to support a few gold fish and a few lettuce plants in such a "simple" system, I expect as soon as you try to increase things to the point of being able to regularly eat from it, there will be problems.

So is there truely no electricity to be had at this site? There are some small pumps that could probably be run from a battery being topped up by solar or wind of course adding the solar and wind and battery really increases the complexity of the whole set up. One would need to make sure to get a battery that can deep cycle without being worthless in only a few cycles. (simple car battery would not do for regular operation like this, drain a car battery down way low a few times and I may not be able to re-charge very well anymore.) A good high amp hour deep cycle battery (marine batteries are often a good place to look) often needs a special charge controller that is a little different from a regular car battery charger. They usually need quite a bit of power for a good re-charge so one would need to make sure the solar panels were adequate to the job.

There are some hidden complexities to the floating raft. First you need the raft material and you need to protect it from the sun. Then you need to put holes in it and have net pots for the plants. Then you need something to put in the net pots to hold the plants. And often you need to start the seeds separately from the system and then transplant them. And if it is gonna be in the fish tank, you need something to protect the roots from the fish. If the plants are gonna be larger plants, you then need some sort of external support to keep them from tipping over. Then you need some way to lift the whole raft out of the system to harvest and transplant in the new seedlings. Oh, and how do you feed/see/or harvest your fish if they are hidden under a big raft over the fish tank?

Sorry, I just don't see raft systems as simpler. About the only thing this idea has going for it is the possible ability to take place in one container. Like perhaps if the orphanage already has a pond or dam that is stocked with fish and stable already. If they were to add a floating raft with root protection to it, add a air bubbler, and up the feed for the fish a bit, then this idea might work but I doubt it would actually grow very many plants.

Personally, it would probably be simpler to give them a copy of the barrel ponics manual if they want an aquaponics system as an educational tool. Then if there is access to computers/internet interested children can research improving their knowledge of aquaponics and design their own system that would be appropriate to the people/materials/tech on-site. If this is a system meant to feed the children, then definitely go with something that is tried and true like an actual commercial system or flood and drain gravel beds.

Totally agree TCL...

This is excellent advice, thanks.

I certainly wouldn't recommend an orphanage adopt a newfangled method that has no proven success! However, the articles posted appear to suggest the idea has merit.

It was more that it triggered this thought experiment on my part - just how simple could you make a system? It would be an interesting challenge, that's all. Or perhaps more to the point - how low could you get the power usage? Aeldric's system apparently runs off a $130 solar panel and battery, so perhaps there's no need for reinventing the wheel.

Here's a way I was picturing filtration and aeration occurring simultaneously:


The pump need only be small as it only has to produce a small fountain. This would of course necessitate an area of open water not covered with rafts, so that the fountain water actually lands in the tank and creates a splash.

An alternative would be to have a similar vertically-oriented filter (such as the one shown, like a perforated barrel full of gravel) plonked somewhere in the tank and rely on water flowing through it, then provide the flow + aeration using a paddle wheel.

Hmmm... I think I need to go away and read about what's been done before!!

I don't know that we ever really got any updates about how Aeldric's system did in the long run though

There are materials that make really good bio-filter and can support bio-filtration for a huge amount of fish in a much smaller space than gravel needs. However, these bio-filters are only bio-filters and there would need to be a separate solids handling system that would likely need regular cleaning if stocking is high enough to feed an orphanage. So far, I don't know of any systems that can support huge numbers of fish and plants using only a 4 watt solar panel and 12 volt battery for power. I'm sure you could keep something perhaps the size of a barrel ponics system running on minimal power like that but one of those systems only supports about 12 adult fish, perhaps more if attached to a duckweed pond as I have done and added a supplemental air pump.

Maybe the trick would actually be low stocking densities, and accept that the system would have a larger land footprint. One can't win on all fronts, but perhaps that's the price you have to pay for a simpler and lower power-consumption system?

I'll give it some more thought. This article by Ron Zweig is good:
http://www.nature.my.cape.com/greencenter/pdf/zweig.pdf

Seems to have some of the "science" in there, including calculation of a nitrogen budget for the system - i.e. how much nitrogen goes in with the fish food, how much comes out when you harvest the lettuces, etc., and therefore how much biomass of fish do you need to produce a certain mass of plants per week. Interesting stuff!

Zweig's ponds seemed to have 3 aquarium air bubblers in each - so these would only be on the order of several watts of power consumption each, so maybe 10 watts per pond. Each pond then has around 5kg of fish in it.

Hmmm... 10W for 5kg = 100W for 50kg. Perhaps the power saving is not actually that big compared with, say, my system (80W for 20-30kg)? The point is more that it is really just a smaller system.

Right-o. Back to the drawing board...