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OK...I sadly admit that I"m about to give up unless someone here can show me the way to get this stuff to grow!.  I've had two black bins, each about 6 - 8" deep with water (I let it fluctuate quite a bit) that I put duckweed in in late June and it hasn't done a damn thing.  It is relatively shaded, gets no extra oxygen, and has had several doses of fish water, alternated with dechlorinated hose water.  I"m starting to grow some lovely algae but no duckweed....can't believe I can't grow a weed!  Any thoughts?

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Hey Sylvia! I haven't started on duck weed yet but I have the room, and want to. Mine will be indoors, and I'll check with some friends that have been successful. My wife is totally amazed at what I've accomplished so far, and now I can cut loose some funds for more equipment, plus I get to attend the seminar in Denver next month WOOHOO! 100% success here!!! I'm stoked.
Hey Dano, so psyched I'll get to meet you in Denver! Don't wait too long to sign up, if you haven't already. I heard from the Botanic Gardens that it is filling up fast. The room only holds 35 and I'm sure it is going to sell out in the next couple weeks.
Duckweed seems to grow best where you don't want it. I've found it seems to grow best in water that has some ammonia in it. If you are giving it filtered water that really only has some nitrates, it may not thrive.

Challenge is how to provide water with ammonia to a bin you don't want filling with the solids.

I've not figured out a way to grow ample amounts of duckweed to actually provide more than an occasional treat to the tilapia. I had a 16 foot long by 28 inch wide tank running for most of a year to grow duck weed and if I put half a dozen tilapia in it and didn't feed them any pellets for a week, a thick layer of duckweed would be gone by the end of the week. If I fed pellets, the layer of duckweed would remain.

We had to go to the pond in the woods where we got the duckweed several times to replenish. You need a really large surface area of not full sun water that doesn't get too hot in order to grow much duck weed and the duckweed definitely grows better with some ammonia input since it is one of those water plants that can use the ammonia directly without the need for conversion to nitrates first.
So could the solution really be as easy as suggesting my hubby have a pee party? He hasn't been able to do that since the last AP system we cycled...he would be thrilled!
If you are ok with growing duckweed peeponically to feed the fish? Make sure it is a really small pee if it's a small bin or it might start to smell.

Sylvia Bernstein said:
So could the solution really be as easy as suggesting my hubby have a pee party? He hasn't been able to do that since the last AP system we cycled...he would be thrilled!
For a little ammonia and a little fun...sure...;-)
No. Not as much fun as a pee party, but I'll give it a shot. thanks Ernie. By the way, your pot-in-the-tank idea worked great. Everyone settled down. Amazing.
I've killed Duckweed Sylvia by adding too much nitrogen fertilizer to the water. It seems to grow well if there is no visible surface disturbance of the water and the water is stagnant or slightly brackish. I have seen it die in full sunlight with too much heat. Grows fine is dappled light. Maybe your black bins get too hot?

"Growth conditions The natural habitat of duckweed is floating freely on the surface of fresh or brackish water sheltered from wind and wave action by surrounding vegetation. The most favorable circumstance is water with decaying organic material to provide duckweed with a steady supply of growth nutrients and trace elements. A dense cover of duckweed shuts out light and inhibits competing submerged aquatic plants, including algae."
More info : http://www.p2pays.org/ref/09/08875.htm
I have also heard of the opposite problem. Duckweed growing like crazy. I am thinking may be a temperature issue. In these conditions, it seems like it may be creating low oxygen in the water because of the decomposition process at the bottom of the tank(s).
Sylvia- there are many species and varieties of duckweed, each with it's own set of requirements. most duckweed however likes moderate (dappled) to full light and relatively stagnant water. your nut. req. will depend on the duckweed- and actually, the duckweed that thrives in different systems will be a little different (usually). I recommend trying as many different varieties as possible before giveing up. I had to try several varieties and it took a couple months before my duckweed really took off. Now i can't get rid of it fast enough and have to remove 3-4 pounds every 4 or 5 days to dry and feed to my worms. if you'd like a sample of my duckweed let me know- you're close! I can also get you some wild strains with low N req.s.
We have also seen that duckweed grows best when the water is still.

Frank Gapinski said:
I've killed Duckweed Sylvia by adding too much nitrogen fertilizer to the water. It seems to grow well if there is no visible surface disturbance of the water and the water is stagnant or slightly brackish. I have seen it die in full sunlight with too much heat. Grows fine is dappled light. Maybe your black bins get too hot?

"Growth conditions The natural habitat of duckweed is floating freely on the surface of fresh or brackish water sheltered from wind and wave action by surrounding vegetation. The most favorable circumstance is water with decaying organic material to provide duckweed with a steady supply of growth nutrients and trace elements. A dense cover of duckweed shuts out light and inhibits competing submerged aquatic plants, including algae."
More info : http://www.p2pays.org/ref/09/08875.htm
I've got 'giant duckweed'..(.kind of like saying ...'jumbo shrimp'.) It is easier, to keep it where you want it, it's bigger size doesn't go through screens so easy.
I have a 3/4 inch line going to the bottom of the pool. It has a slip cap on it, which has two 1/8 inch holes drilled in it. Very little flow. Now that it's so hot....I've been putting shade cloth over it.
I give half of it , every day, to the fish.....The tilapia love it..even my goldfish eat it. I haven't actually seen the cats eat it...(?)

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