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 Post subject: Duckweed - Friend or Foe
PostPosted: Jan 12th, '16, 11:51 
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While I was removing some scoria from my grow beds, I noticed the duckweed that I fed to fish made into the GBs and growing all over. I am not sure the extent of it as I didn't dig into the GBs more than I need to. GBs are on bell siphons.

Then I was reading on Wikipedia this:
The plants can provide nitrate removal, if cropped, and the duckweeds are important in the process of bioremediation because they grow rapidly, absorbing excess mineral nutrients, particularly nitrogen and phosphates. For these reasons they are touted as water purifiers of untapped value

I am worried a little. The veggies that are on top seems to be growing okay though a little slow. I am thinking may be duckweed in the GBs are pulling most of the nutrients along with nitrogen.

What do you think dear forum members? Would this be a problem for veggie production. It is all good for the water chemistry and the fishes though.

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PostPosted: Jan 12th, '16, 12:01 
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Yes they can be a problem for veggie production because they grow so fast. I reduce the amount in my system periodically and put it in the compost heap for my dirt garden so the nutrients aren't wasted and the plants in the AP can get more of the nutrients the fish are putting out.


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PostPosted: Jan 12th, '16, 15:31 
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I suspect duckweed is not ideal in your grow bed as they will be in direct competition.
Also maybe indicates that your growbeds are bit too wet ?

Usually if you are wanting duckweed it is normal to have a shallow water bed (similar to a DWC bed) on the side.
Then just skim it off as needed and if you have too much add it to the compost.
Usually have to do that approach because it does not last too long in with the fish (and tank is shaded)

no doubt about the fact that it goes off when the nitrates are up and there is a bit of sunshine.

on your pumping/GB feed - what method do you have that the weed could get to the GB ?
if direct pumping from FT then presumably the pump should be near the bottom and if a SLO then it should also be extracting water from the bottom.

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PostPosted: Jan 12th, '16, 16:23 
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Personally I like it because I have goldfish and it gives them a little roughage (spelling).
As Darren said it should not be growing in your GB's, your flood level is too high, and possibly it is keeping algae (which is worse) at bay atm.
High nitrates might be ok for certain crops and at certain stages of development but it isn't good all of the time. :)


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PostPosted: Jan 12th, '16, 16:46 
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If you have vegetarian fish they will love and when you get too much if you have poultry they will love it too.You just need to control it.

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PostPosted: Jan 13th, '16, 10:29 
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I wouldnt worry too much about the duckweed, if not harvested it will eventually break down in the grow bed and release the nutrients anyway. If you do harvest any just feed it to the fish.


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PostPosted: Jan 13th, '16, 11:22 
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Thanks for the replies guys
dlf_perth wrote:
on your pumping/GB feed - what method do you have that the weed could get to the GB ?


Yes I pump direct from FT to GB and the pump is at the bottom. Aeration took some of the duckweed down to pump and they went into the GB from there. GB is about 4cm high from the water level and the duck weed is inside. You can't see them unless digging in.

I grow duckweed in a separate bucket and feed to my silver perch fingerlings from time to time.

Looks like there is no need to worry. They will break down in time.

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Fish: Trout / Silver Perch
Hailea 80 air pump
1FT-1RFF-4GBs-1ST
Gurkan The Cheesemaker
Pictures of My AP System
My site


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