Backyard Aquaponics
A place to discuss aquaponics

Duckweed is at the end of a 4' x 40' x 10" floating raft bed. It is spreading slowly but has been 30-50% white/dead since adding it. My pH is about 7.5 and nitrites/nitrates/ammonia are all at 0 (fish are still small). I am also getting NO plant growth with the lettuce in the raft. I start them in coco coir filled trays and transplant into raft after 2-3 weeks. My system is about 6 months old. I have a 250 gal IBC fish tank with about 20 koi, I recently added two larger koi due to the 0 nitrate level. I feed pellets with 40% protein 2x/ day. This is inside a hoop house with roll up side ventilation and 40% shade cloth on top. Ive tried adding maxicrop plus iron but notice no difference in plant growth. Do I have to add more fish or just wait until they get a little bigger and get some nitrates in system? Ive seen lettuce grow with 0 fish/ nutrients so Im really at a loss here.

how much light is the duckweed getting ?

>> I have a 250 gal IBC fish tank with about 20 koi
things will probably work once the fish get a little bigger.
Think twice about increasing number of fish because you may end up with too many once they get larger
(which happens quite quickly in warm weather)

under 40% shade cloth

> under shade cloth
in summer that shouldn't be an issue - but temps up to 60-70 will benefit from no shadecloth.
Benefits only really kick in once hot,dry weather starts.

Otherwise probably just the nutrients.
One option is to take some duck weed and put it in a tub (like childrens mini sandpit/wader).
Add a *little bit* of seaweed extract and see how that goes.
(just may have to deal with mozzies - perhaps some small robust fish)

Duckweed doesn't like currents/rough water.
So you may need your duckweed to be slightly offline with a smaller flow.

not sure what species of duckweed - do you have pictures
how to post pics > viewtopic.php?f=4&t=21754
that is the other variable.

try giving the DWC plants a gentle (very low concentration) foliar feed.
what method do you use for the DWC plants (eg. baskets and media, foam grips etc)

I wonder if you try raising the rafts a bit to create an air gap or add some air into the DWC.
But without pics hard to say.

DWC was built about 3-4 months ago, I built the initial system last winter so everything is cycled and I have a SLO pipe from FT to swirl filter followed by a bio filter oxygenated by venturi, than that drains to sump

I added shade cloth about 6 weeks ago when temps inside got above 115, I also added roll up sides and a high velocity fan to help push the heat out around that time. I've been planting about every week since I built the DWC bed when it was in the 40s every day and no matter what the conditions are (hot/cold/shady/sunny) nothing will grow past the second pair of true leaves.

I start seeds on a NFT bed in small cell plug trays with coco coir & some mycorrhizae and cover with vermiculite. I get great germination and in 2 weeks I transplant after they have 1-2 sets of true leaves

DWC has air bubblers every 4 feet with floating rafts that are 2" thick, so there is an air gap between grip plugs and the water, but transplants roots werent strong/long enough to reach the water so I've lost a lot of seedlings.

Now I float transplants for a week or 2 before placing in the rafts so it gives the roots a chance to develop



At what strength should I mix my maxicrop plus iron to try foliar feed?

Your pH is too high to get any benefit out of the Maxicrop plus iron if you are adding it to the system water. You could spray it on as a foliar feed or use an Iron Chelate like EDDHA or DTPA iron (Not EDTA it won't help at this pH).

Sounds like a nice setup - post up some more pics