Duckweed beds are a problem?

[Louise]

In another thread Vlad wrote this to me:

"You may (or may not) want to reconsider growing duckweed in a tank that is directly connected to your AP system...It might be wise (judging from some of the horror stories) to grow the duckweed separately in another tank. But that is not anything that I have direct experience with, so check with someone who does..."

Please direct me to some useful information on this.

[nimrod bash]

well i dide but thees thing seem to b sucking a lot of iron out of my system

am adding iron only when i c a deficiency and at the time i had that in my system i needed to use

2.5 times more iron S:

only point i c of growing it in your aquaponics system is to grow more fish and less vegetables ...

and depend on the type of fish u grow there might b e better ways to do that ...

[Louise]

Well, my objective is not to grow more fish than vegetables. Partly it is to utilize space. Since I have cut an IBC tank in two parts, one for the fish - the other part is an excellent grow bed. Either I could use it with media in, and veggies, but since it will, in my system, be a little more difficult to reach into, I thought a floating culture would be good, since I can easily wisk it over to my side.

The other reason would be to feed my fish, hens and ducks with this excellent protein-rich plant, that has growth rates that exceed most other plants!

Adding iron doesn't seem such a horror story to me, what are the other problems with it?

[nimrod bash]

well u will need to grow more fish

nothing come's from nothing ...

consider it as another grow bed only as far as i can tell from my experience it use more nutrient's

abut 2 time's as DWC of the same size full of green's ...

and it probably will landslide win a competition over nutrient's vs veges 

what happened to me is: NO3 dropped to 0 over time and it barely affect the duckweed and starved

my vegetables

witch my guess is duckweed can use nutrients at lower concentrations the vegetables

therefore potentially it can be really bad for the vegetables...

[Louise]

Aha, I see! Well, it makes sense - if the duckweed produces enormous amounts of biomass, rich in protein - it will need input! Seems like I should have a barrel on the side and add duck weed and duck poo to it, and see what happens! Maybe some aerator too?

Since my accessibility problem could also be solved with rafts of lettuce, that I can pull towards me, I might better use the top of the IBC as a normal deep water bed.

I didn't really catch the sentence on landslide.... Sorry, not native English speaker.

nimrod bash said:

and it probably will landslide win a competition over nutrient's vs veges 

[Vlad Jovanovic]

All nutrient issues aside (for now)...the stories I was referring to were folks who had all raft systems were the duckweed tends to 'escape' from where you wanted it to be, and grows everywhere, and clogged things up... wreaking general mischief...

Now, I'm sure that you, like many have probably read that duckweed has a protein content of somewhere between 35% and 43%. Sounds great, right? But those numbers need to be looked at in their proper context (realistically). Those protein numbers pertain to a DRY WEIGHT basis, and since 'fresh' duckweed is about 99% water...your only looking at 35 to 43% of that ONE PERCENT! Not so great anymore. You're gonna have to grow A LOT of duckweed to even make a dent in your finned friends dietary needs (and hence your plants needs to grow even somewhat well). Then you need to take into account that if you do want to dry and store the duckweed, you cant just set it out in the sun (or whatever) to air dry. Well, you can, but a significant amount of that 35% of 1% nutrient value will then degrade resulting in even poorer nutritional content...You need to have a way to vacuum freeze dry the duckweed if you wish to lock in a good part of it's protein content. 

Also, if you're paying good money to feed your fish quality fish feed, so that you can grow duckweed...to feed your fish...that seems like a pretty silly and EXPENSIVE strategy. It seems the thing to do is grow the duckweed using a free source of nitrogen. Since duckweed seems pretty adept at utilizing N in the form of NH4 (ammonia) to grow...humonia seems to fit the bill nicely. Humonia has an NPK value of about 11-1-2 with some other minerals in there...and it's absolutely free...abundant, and totally sustainable...

Again, I've not nor do I wish to grow duckweed...the above info comes from people who do/did. Look to folks like Mr. Carey Ma and others for pointers on making your own quality fish food. Carey knows A LOT about a great many things...and has much realistic experience in 'all things sustainable'...meaning, without all the hippy bullshit or half truths.

..."by a landslide..." means by a large percentage or amount...  i.e "...he won the election by a landslide..."

[nimrod bash]

"pretty adept at utilizing N in the form of NH4 (ammonia) to grow"

that's explain a lot of my experience with it in my system

i also had a spike of NO2 wen i removed it from my system

so i guss it's basically uncycle my system ...

vlad i must say i enjoy your post's (:

[aubrey sloan]

I thank you Vlad,my next thought was to hit the local ponds looking for the duckweed. Didn't want to wade in muck anyway.

                                                                     

[Paul Smith]

Hi all,

Duckweed is just THAT, a WEED!!  I have seen shows on Animal Planet, where people go after alligators and snapping turtles in ponds in the Southern U.S. were duckweed is growing several inches thick on the surface.  Here is Western Washington, where anything will grow if you put it in the ground; I live in fear that this WEED will get loose in the environment!! We don't need it here.

I purchased some, what I thought of at the time, cheap gold fish from Petco, 29 cents each.  I brought them home and released them in my fish pond in the back yard.  A few weeks later, here growing in my pond, is duckweed.  I returned to Petco and complained, the only response was, "Well everyone has duckweed."  The idiot at the store had no Idea that this can cause a tremendous environmental issue.  I am looking for  someone in State Government to make comment.

To get rid of the duckweed in my pond, I will have to completely remove the whole system right down to the sand in the ground and completely rebuild it from scratch.  I don't think I can even remove the water, kill all of my fish, and sterilize the liner to get rid of this noxious pest.  One microscopic piece of this plant can reinfect the whole thing.  Folks, when you mention anything about this weed, I shudder.

His and Your Very Grateful servant, Paul

[Jon Parr]

Interesting angle, Paul. I certainly agree that duckweed is invasive, but that should not be confused with non-native. In my area of central Cali (and possibly your's too?), duckweed is a native plant and it supports the environment and the native species that eat it. The notion that your duckweed came from the pet store may certainly be true, but it is also eaten and spread by, you guessed it, ducks (and dogs, people, every bird that touches water, etc). If your pond has access to nature, then DW is bound to end up there sooner or later, as is nature's way. 

The good news is that duckweed can be fed in surplus to your fish, and does not foul the water. It's a great means of storing nutrients and energy, and for blocking algae. If you have nutrient, light, and water in the same spot, you will have either duckweed, or algae, so take your pick.