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Is it possible to reproduce Duckweed along with Tilapia in an IBC tank? Goal - Lowering ammonia & oxygination with DuckWeed, while avoiding over feeding.

I could not make the duckweed proliferate in my Tilapia tank. They would not give it a chance to thrive if it was placed in their tank. This made me ask myself: What would happen if I added an abundance of duckweed in my Tilapia tank?, Would they feed on it endlessly until their deaths? Would there be enough surface area in my IBC tank for the Duck Weed to thrive along with  110 Tilapia?

I also heard that I may need a larger surface area to enable more Duckweed growth perhaps implying a shallow Tilapia tank or having less Tilapia per gallon? It sounds to me that the only way to have a constant supply of Duckweed for Tilapia may be in conditions of a shaded shallow pond with a low or moderate population of Tilapia.

My aim is to make the Duckweed lower the ammonia and oxygenate the fish, and so far I may have achieved this to a a degree by keeping the Tilapia from reaching the Duckweed yet sharing the same water. Possible benefits are:

  • It may even bring down you electricity costs because you can use smaller pumps to oxygenate and clean the water.
  • It could be a passive way to keep the fish alive if you lose your electric power.

I know Tilapia, given a choice, like to vary their diet; but I just don’t know if they would stop eating the Duckweed after a certain point. My guess is that they would search for something else to feed on after they get their fill on the Duckweed; and they would not overfeed to death. But it’s just a guess I really do not know. Has anyone tried to reproduce Duckweed in a Tilapia tank that could help answer my questions?


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Now there is a good use of that upside down shelf growing idea!!!!

Dennis McClung of came up with the shelf idea. He filled the trays from two shelf units with hydroton (I wouldn't recommend anything heavier), set a 10 gallon aquarium on the bottom shelf and grew an entire salad on a 2'x2' footprint. We did the same for a while. It's a great idea for patio homes and apartments. Dennis also started the shelves for duckweed and we just expanded on his ideas. :)

I remember the original ShelfPonics that Garden Pool showed off and I remember thinking that was not much media for filtration and not a whole lot of room for plant roots and therefor a very limited system.  I've used the general idea for seed starting and seedling displays but the risk of root clogging kept me from doing a whole lot more with the idea.  I like the duckweed shelf idea though, seems a very appropriate use of such shallow containers.

You're right, the shelves don't provide the benefits of a larger, deep bed garden, by any means! But, they will grow a lot of crops (lettuce, cherry tomatoes, radishes, chives, etc.) without root problems unless the plants stay in for a long time. They require cleaning out every 6 - 12 months because of the filtration issues. It's not a system of choice for serious gardeners, but it's a good system for people who want to grow a small garden, have little or no garden space, want to 'test' aquaponics, or for a kid's garden.

For duckweed, I use the top shelf as a pre-filter with standard aquarium filter material in it because the water is part of our main system and it has solids in it. Even so, stuff builds up under the DW, so we vacuum (siphon) it out every month or two. Our best DW tray is a 7" deep hydroponics tray that is filled about 1/2 way with water. It has a smoother bottom and is a little deeper, so I can scoop out DW easier without catching solids, and it's easy to clean. The shelves work fine,too, but the ridges in the bottom and the 1.5" water depth make cleaning and scooping a little more of a challenge.

Good details, thanks Sheri!

Your welcome! If you play with it, let me know what improvements you might come up with & I'll do the same. :)

I have found, as others have pointed out already, that the duckweek either needs to be in seperate tanks, or in a protected flotation system, otherwise the fish eat every last ounce of it!

I just read your duckweed blog and I must say well done. I have a question. I think in a couple of months my fingerlings are going to outgrow my systems ability to filter the water. If I read your blog correctly I can use a duckweed tank/pond to help in filtering the fish water while providing a favorable situation to grow the duckweed? I have an IBC full of water and covered in duckweed that acts as a water return from my GB to my FT. Is this a good system? The duckweed grows but not at the rate I've read about.

TCLynx said:

I've written lots of posts about duckweed.  Unfortunately I never seem to have time to go searching for them to link my repeat answers.  So I finally wrote up a blog post on the subject.

TCLynx on Duckweed

Maybe but it really depends on what factor is actually limiting your duckweed.

is it growing slower because of the amount of available nutrients?  Too much water flow/splashing? Too little aeration? Or Too much or too little light?

Duckweed can grow amazingly fast under ideal conditions but too often people expect the amazingly fast growth under far less than ideal conditions and they are disappointed.

And, duckweed being a weed has that odd quirk.  Do you know what a weed is?  A weed is any plant growing where you DON'T want it.  Therefore when you DO want it growing there (and it therefore is no longer a weed) it seems to not grow like a weed anymore.

Just put 800 1" Tilapia into an IBC covered with duckweed. It started disappearing immediately. Hopefully I salvaged enough to start over. I kept feeding them too so it's not like duckweed was all they had to eat. BTW what do you call a 1" fish... fry or fingerling?

Jeff you won't be calling them much for long, 800 1" tilapia are WAY too many for an IBC tank.  Tilapia should be eating very high protein feed at that size and to provide enough aeration and circulation to keep 800 of them alive in a single IBC tank means conditions won't be good for the duckweed (they like well aerated but relatively still water.)

1" fish I would probably call fingerlings but they are still quite small.

100 fish in an IBC tank usually makes me say (that is way too many fish.)

Tilapia can grow really fast under really good conditions but when over crowded like that, you may wind up with a lot of completely stunted fish.  Somewhere between 1-3 inches I would want to have them placed out in final grow out location and I generally like to have 3-5 gallons of fish tank per fish if I am trying to grow the fish out to between 6-12 oz.

If you have one of the Larger IBCs that you have only cut a hole in the top and have it filled to rather close to the very top, you probably still only have 300 gallons MAX in that IBC.  How many other tanks do you have ready to go to grade and move tilapia to?

Tilapia fingerlings (from about pumpkin seed size up through when they are about ready to start breeding) have an intense protein hunger, if some are a bit larger than others, they will eat each other.

I just moved them from a 55 gallon aquarium to the IBC. Figured there were 400 at most. I have about 25  2 1/2 to 3" fish that I'm going to move to the aquarium for breeding. Right now I have 2 330 IBC tanks with the tops used as GB. There are only 5 full grown Tilapia in one withe the 25 smaller fish that I am going to move. I'll probably move the larger fish when the 800 get bigger and need more room. I have a 3rd tank not set up yet for future growth. After my first winter I'm thinking of moving the operation to my basement for next winter and grow the fingerlings and back outside for the grow out. This is my first year so I have no idea what I'm going to do with all these fish. But it's a lot of fun. If I had tried to produce fish this year I probably would have had thousands. The two litters I got were 298 and 523. The only fish that I think that got eaten was a Pleco I put in the aquarium. It was about 2" and disappeared.


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