Duckweed

[TCLynx]

Duckweed is a great plant and makes wonderful food for many kinds of fish and other water creatures, however, you need a huge surface area to grow enough duckweed to be the sold feed source for more than a few tilapia.  If you had a few ponds off in the woods behind your place where you could collect huge net fulls of duck wee every other day, you might supply enough duckweed to keep a tank full of tilapia in tucker but...

 

I had a duckweed tank for a while and it was about 30 inches wide by 16 feet long and I could keep the entire surface of that tank covered in duckweed as long as I fed the 12 tilapia in that tank a hand full of pellets each day.  As soon as I went away for a week and wasn't feeding them pellets every day, the entire surface of the tank was cleared of duckweed within that week and I had to go get more to re-start my duckweed culture.  So imagine that a thick cover of duckweed over that surface area doesn't equate to 7 hand fulls (and I have small hands) of 32% protein commercial feed.  For just 12 tilapia.

 

Now if you have the space to set up and fertilize several large shallow pools to grow duckweed to then dry for use as feed for the tialpia, you might manage but it takes a lot of space to grow enough duckweed to be anything more than just a supplement.

[Kobus Jooste]

That sounds like the little root systems of the duckweed.  I do not seem to get it happening with feeding some to tilapia (maybe they chomp the lot) but I do not feed it to the fish every day.  Could be that the koi only browse off the leaves.  While a little fountain pump I have in a water feature with duckweed in it clogs itsself with the roots all the time, my research unit's inline pump has been going for about a year with no service or issue.  Is it possible to modify your system to have the pump in an external sump that operates on an overflow from the fish tank?  That way you could try to have a mesh net strainer between the fish tank and the pump.

[TCLynx]

If you can arrange things so that the surface water can't get to the pump this might help.  As in any tank with duckweed in it should have a SLO drain or venturi drain so that the duckweed stays on the surface but the water is being drawn off the bottom of the tank to go out to the filters and pumps.  Does this make any sense?  I don't remember having any problems with my pump clogging up with duckweed in my old duckweed system and it had a venturi drain or SLO (stands for Solids Lifting Overflow)

 

[Daniel Driscoll]

Im currently planning another project. I "think" I'll be using the SLO, if this is the definition of a SLO, from my 1100 gal tank to my DIY 55gal drum filter. The SLO draws from the bottom of the fish tank, goes through the tank wall at the desired water level, through the 1st drum wall, and then down to the bottom, so the water has to rise up and overflow again into the 2nd bio drum. I'm not sure how I will place a mesh screen since the water releases at the bottom of the 1st solids drum. I had planned on throwing a ball of birdnet in there and then topping it off with some sponges, that might be enough huh? Cleaning would require spraying off both  birdnet and sponges and then vacuuming the settled solids out. I wish I could install an easy drain but my drums will be partially buried.

If the overflow released at the top of the drum a mesh screen would do it nicely.

[TCLynx]

Sounds like it could work.

 

You might be able to stick a drain into the bottom of the drum that you could plumb out and up so you could still suck some of the solids out that way or perhaps even pump some of the contents out from the bottom of the barrel without having to pull out the netting and such.  Perhaps even a sump pump in the bottom of the barrel so you just turn it on for a couple minutes and let it suck the gunk out until the discharge isn't so gunky and turn it off.  Depending on the loading of the system and what small creatures take up residence in the filter, you might not have to be cleaning the netting/sponges that often.  Some aeration above the screen level might be a good idea though.

 

I've just added a netting/sump pump settling pond section to my duck system myself so I can suck out the fine sediment every so often.

 

I'm now thinking about adding duckweed to the sump in my new tower system since I need more plants to take up nutrients and I don't have the budget to buy more towers at the moment.  The tower system is set up kinda like a CHOP 2 system where the pump feeds both the grow space and the fish tank and everything drains back to the sump so there would be a chance for the duckweed to use some ammonia before it all got sent through the filtration. And because it is a tower system and not a flood and drain set up, the water levels in the sump don't fluctuate that widely so I'm less likely to wind up with all the duckweed stuck to the sides they way tends to happen in a regular fluctuating sump.  I might just need to keep the water level in the sump high enough that the pump won't be sucking down duckweed and make sure the water going back into the sump isn't splashing too much for the duckweed.

[Kobus Jooste]

Only thing is those fibers are not at the surface any more.  If the leaves and roots are seperated, the roots end up sinking.....

[Daniel Driscoll]

Yes the sinking roots clog up the hard plastic screen surrounding the pump that lays in the bottom of that koi pond. But a SLO in my new system should grab those along with the other solids. Its amazing to think that the koi could pull the roots off and only eat the leafy part. I thought it just wasnt getting digested and hoping that maybe the tilapia would process it better.

 

I think the sump pump sounds goodfor cleaning out the solids tank. What knida critters will digest leftover plant material in my filter, just little creatures or something like shrimp?

 

I was planning on growing alot of duckweed in my DWC, along with potted and floating pond plants. And if the day comes along to float some raft w/ veggies i'll be ready. I'll probably do some expirementing with some veggies but I've got a feeling the bugs will overwhelm me, especially with all the pond plants alongside. I'm not sure which kind of duckweed I have but im hoping they'll get enough ammonia. I'm gonna stock the DWC with guppies and the likes so they will act as my filter bypass.

[TCLynx]

Hum, I hadn't really thought about the whole, roots hot attached to the floating leaves anymore problem.  I would guess that is more of a problem in situations where the fish tend to choose to eat only the leaves and not in tanks where one is harvesting the duckweed to use elsewhere.  I'm hoping the duckweed might help feed my ducks since I'm not growing tilapia anymore.  I've got that tower system in need of more plant at the moment. 

 

As to the detritivore creatures to eat the stuff collecting in the filter.  Tiny shrimp may do the job and gammarus (?sp) are known to do that job too.  I get pillbugs and millipedes doing it at the surface or water line in gravel beds and tanks.  Worms are of course many people's favorite detritus eaters but they do need a very well aerated situation to survive submerged (but they can if there is plenty of dissolved oxygen.)

[TCLynx]

Here is a comment originally posted by Carey Ma that I'm pasting in here since it is so on topic.

(I thought I posted this before)

Here's my two cents:

I use to collect as much (wild) duckweed as I wanted from the many irrigation ditches/ canals around the village but was a little concerned about any pollutants that might end up in me so I started to grow my own

I grew duckweed in several large long beds (4' x 16' x 5") that flowed directly from the fish tank's and duck pond's solid waste filter. An air pump was attached to the outside connected to three circular air stones and placed in the bottom. A plastic platform with legs and holes drilled into it used to separate the perlite and crushed bricks (like in a wick systems). The filter consisted of air-stones, separator, perlite and crushed bricks with a layer of geotextile in between each layer except for the separator. There I used a mosquito screen. Another piece of geotextile was placed on top followed by a piece of river rock where the water splash. Worms were placed on top of the geotextile to eat up and break down all that fantastic poop.

 

From the duckweed grow-beds, water was siphoned off the bottom of the beds into a connection at the bottom of a bucket. A brick or two was placed in the bucket to deter any plants that might accidentally get in from going across the bucket and directly into the exit hole on the opposite side (idea taken from septic tanks). I simply scoped (netted) any little wanderers off (if any) and added it to the rest of the harvest.

The collected duck weed is enclosed in an old T-shirt with the holes sewed shut and Velcroed, then squeezed and spun dry, after which it is placed in the solar dryer or freezer depending on what I was doing at the time. Either way the dried material was then ground into powder to add to the other ingredients, to make feed.

 

Duck/ Fish pond > solid filter > Duckweed beds > bio reactor > grow beds 1-6 > cistern + oxygen > fish pond > duck pond

[Conrad Chin-Yee]

Today I got 3 buckets full of duckweed. The fish can't eat all of it right now. I put some to grow into all the containers I have and still have lots left. Can I dry it on window screening in the sun and then fee the dried duckweed to them later?

Conrad

 

[TCLynx]

Sure I don't see why not.  Or you could freeze blocks of it to save for later too.