Backyard Aquaponics
A place to discuss aquaponics

Hey guys, I came up with a design for a all-in-one DWC raft system. Before I attempt to build it, I'd like some feedback on what may possibly go wrong with this system and any suggested improvements.

The idea is to have a DWC system partitioned into 3 different zones:

1) Fish Zone
2) Root Zone
3) Bio-Filter Zone

Suppose our tank is 10m in length and 1m in breadth. Since the fish are likely to eat the roots of the plants, the root zone can be protected from the fish using some type of wire gauze that extends laterally across the length and breadth of the DWC tank. On the base of the DWC tank, we have a enclosed Bio-Filter zone which spans the width of the tank. A water pump is used to push the feces of the fish along the bottom of the tank, into the Bio-Filter which then processes the feces.

The water pump will create a natural circulation in the system. On the left end of the DWC tank, there can be an opening for feeding and tending to the the fish.

Any problems with this design? Thanks

How do you get out dead fish?

Thanks for the response! Good question. Maybe the gauze structure can be removable instead of fixed in place? So if a dead fish is under it, we can simply unclip the gauze from the tank and slide it out like a sheet of paper.

You can build the wire material together with the raft to save the roots ( so if anything happens, you get easy access to fish and bottom of tank ), but you cannot get enough filtration with this setup.

Solids removal?

Good point about the wire material with the raft. Filtration has been a concern of mine and I realize that the stocking density of the fish needs to be lower than that of a regular aquaponics system. I need to find out what the required number of fish are to sustain 10 square meters of growing space. By controlling the amount of feed into the system, one can regulate how much fish waste is being generated. With the bio-filter and the bacterial growth on the bottom of the rafts, perhaps a nice balance can be found, as is sometimes found in a well managed hobbyist fish-tank?



The solids might not be as much of an issue since the stocking density of fish is lower than regular aquaponics. I read this article https://www.friendlyaquaponics.com/2015/08/04/1714/ about bio-filters and assume that if I maintain my feeding regiment correctly a balance could be found without needing to be too concerned about large solids removal. I'll be interested to hear your opinion on that article.

You can find the ratios even on this forum, but for the growing greens you need X amount of fish. For X amount of fish, you need Y amount of filtration. This Y will be bigger than your tank bottom.

If you have a growbed above your FT, you can have better results I think.

So I made some calculations to determine the amount of fish in my proposed system.

I based these calculations off of commercial aquaponic growers, so I assume their numbers work.
1m^2 of growing area requires 60g of fish feed a day
10m^2 of growing area requires 600grams of feed a day
Thus the system will need to have 600g*365 = 219kg of feed a year
Tilapia have a feed efficiency ratio of .59
With this much feed, we expect to reach 219*0.59 = 129kg of Tilapia in the system.
Each 1lb of Tilapia needs between 2 and 10 gallons of water
Thus the DWC tank must be larger than 129*2.2*2= 567 gallons = 2146 liters
The DWC tank has dimensions are 10m*1m*0.7m = 7000 liters
So we are good on the parameters of fish mass to m^2 of plant area and we are good on fish mass to volume of water.

The only remaining variable is filtration, which is a confusing since commercial growers such as: https://www.friendlyaquaponics.com/2015/08/04/1714/ say they have enough bacteria on their rafts to consume all the fish poo. They also say they don't use swirl filters and bio filters since if you feed your fish correctly (good food and don't overfeed and don't overstock), airstone bubbles will break apart the oily poo to a small enough size that it isn't a problem for the system.

As you said, the variable Y needs to be addressed and taken care of. Given that commercial growers with similar fish to plant to volume ratios are able to address the filtration issue, why couldn't this system? The proportions are mathematically similar.

Considering the size of this DWC tank, there is more than enough space to create a bio-filter (if we need one) in the tank itself. If we were to create an underwater bio-filter, how could it be done?

I'm just throwing ideas out there, so I will be interested in your feedback

I don't see the depth of these zones. You may be surprised how long and bushy roots in a DWC can get.

Imo you dont want circulation pump seperate from filter, the filter should be at the intake of the pump, then all solids will be drawn throghu the media, and not circulated around the roots etc.

Also, far more ammonia is produced via respiration... its not all in the poo!

That's a good idea. Maybe some large sponge structure encircling the circulation pump and airstone? My instinct says a system of this size is going to need 3 or 4 air-stones in total to support the bio-filter, fish and plants.

It seems that 12 inches is sufficient for the root zone in a DWC system. Since the fish need to swim under this root zone, perhaps another 12 to 20 inches is needed? Overall, I think the entire tank has to be at a minimum height of 24 inches total. It seems that Tilapia should tolerate this depth as they do work as aquarium fish -- most home aquariums are not that deep either. My other concern now is that maybe some Tilapia may get stupidly trapped under the gauze and not know where the feeding/breathing trough is

Your main goal is to find the lowest fish density for the plants. Some say 0.1 - 0.2 lbs fish per sqf of growbed. Sounds low to me, but they say it works... you have to test it. ( I guess it depends on the plants as well, like tomatoes will need more than basil )

12 inches root zone + at least 12 inches for fish + another 12 inches for media ( filter ).

You are looking at a tank that is about 40 inches high, which is still OK, if the system can handle the fish waste.

I was thinking about a similar system before, but with the extra filtration from crayfish. They eat every organic materials that fish don`t. Just not sure how they will effect babies, as fish and crafish tend to eat eachother`s babies, and I want a growing population so I don`t have to buy new fish and crayfish as we eat them

Well, hopefuly you can set up a system like this, and let us know how it works.

If you can, build a 60 inch deep tank, so you can have enough space for everything, and do not forget the aeration for the media too, so place the bubblers right at the bottom. I would really love to see a system like this working.

I think for DWC systems, leafy-greens (lettuce etc) are the best bet . If we try tomatoes, then maybe a flood and drain media bed is better (media beds can also act as bio-filters, which is a big bonus)


Yeah, the tank is going to be so big that perhaps making a long rectangular fish-pond out of cement will be the best bet. If this system fails, it can easily be turned into a koi pond, so it wont be a massive financial risk.


Well, baby Tilapia might be a nuisance since they might get through the gauze and chow on the roots of the plants. Perhaps crayfish are a good thing to have then? If the tank was even deeper, one could partition off the crayfish from the fish with another gauze layer (which allows the baby tilapia to get through so the crayfish can chow on them )? So we could have the crayfish and the biofilter as one zone, then have the fish zone, then the root zone (all partitioned from one another by a gauze net)

That would be great. If a system like this does work, then it really is a low maintenance design (no plumbing, no leaks, aesthetically pleasing, economical in terms of space used). The biggest downfall is the potential expense, but maybe its worth it for the low maintenance aspect of it.

If you have some extra space, than you simply cannot fail. This is why:

Floating rafts and leafy greens are no problem for sure.

Fish density: you start with recommended low, and see what happens. If the system can convert fish waste to nutrients for the plants, and its not enough, you just add more fish.

Crayfish: even if tilapia eats the babies, you have an extra filtration, you just have to move the mother for hatching.

Filtration: if the filtration is not enough you can add an extra growbed with media, so you will have leafy greens in DWC and tomatoes or something else in the media bed. ( extra space, bit plumbing and extra pump needed )


You will most likely fail on filtration.