Duckweed Harvest

[GaryD]

Hi,

Today, we conducted our first duckweed harvest since we established our new system which includes a duckweed tank.

1. A thick mat of duckweed on the water surface.
2. Today's harvest.
3. We put the duckweed into small plastic moulds.
4. .....and then put into the freezer.
5. The duckweed tank following the harvest. We simply replace the cold frame and let the duckweed do its thing again.

The frozen duckweed biscuits are taken out as they are required. We simply snap off what we want and float it on the surface of the fish tank. The fish simply help themselves as the duckweed biscuit melts.

No, the large plastic container in the freezer is not Murray's lunch.....it's our winter stock of frozen Black Soldier Fly larvae.

Gary.

[fishfood]

Gary whats the 3 black pipes going to or from the duckweed tank arent you running it with the fish system

[anniefish]

Hi Gary,
Roughly how long does one of the duck weed patties last? I know it would depend on how many fish you have. Mrs D must be understanding, having duckweed and black fly larvae in the freezer :D just watch she doesn't get creative in the kitchen!!
Anniefish

[GaryD]

Hi Annie,

It does depend on how many fish are eating it. I suggest when feeding anything that you begin with small quantities and wait for the fish to clean it up before they get more.

Several species (mostly the omnivores) will eat duckweed but they may take a while to get used to it.

That particular freezer is in my shed. I experienced Navy cooking for six years, so I've eaten worse things than BSF larvae and duckweed.

Gary

[GaryD]

Hi FF,

Two of the pipes are drain lines from the satellite pots and the third one is the nutrient supply line.

Here's why we did it.......



I originally set the system up so that it would operate off of the pump that feeds the grow beds but I decided the pumping cycle didn't quite suit this system.

I've used a separate 20 watt pump to feed the satellite pots. It operates off an electric timer and runs on a 15 minutes on 15 minutes off cycle through the day and a 15/45 cycle during the night. I placed the pump in the duckweed tank and the water drains back into the same tank.



Gary

[GaryD]

Hi,

During recent weeks, I've been conducting regular harvests of duckweed from the 500 litre duckweed tank attached to my system.

I've found that the easiest way to store duckweed is to freeze it. It can be dried....and that would be the logical way to go if using very large quantities.....but freezing is perfect for the backyard fish farmer. It retains its vitamin content and you can store a lot of the stuff in a small space.

We place the freshly harvested duckweed in small plastic containers before freezing it. After freezing, we turn the 'biscuits' of duckweed out of their little moulds and place them in a plastic bag.

To feed the duckweed out, I take a biscuit and tap it with a small hammer to break it into several pieces. The pieces are just thrown into the tank where the fish attack the pieces of duckweed......pushing ithem back and forth across the tank.

Fresh duckweed can get churned up in the water and find its way into the pump. I've discovered that feeding frozen duckweed tends to avoid this problem.

Gary

[wey2go]

Anybody has experience with: http://www.duckweed.com.au/?

[GaryD]

Hi,

Here's a glimpse inside my duckweed tank. The tiny plants have formed a thick mat. Covering the tank with a small cold frame keeps the duckweed nice and clean and keeps the temperature up in the optimum range.

I harvested this lot using a large kitchen sieve. It's currently in the freezer turning into fast fish food.


Gary

[Sunshine]

gary,

What is the "cold frame"?

[GaryD]

Hi,

The cold frame is a little mini-greenhouse arrangement that I put on the duckweed tank.

It comprises an aluminium tube frame clad with heavy duty greenhouse plastic. It keeps the wind-borne debris (dust, leaves and twigs) and cane toads out of the tank while helping to keep it warm.

You can see the cold frame in place on the tank......here (http://urbanaquaponics.blogspot.com/2007/10/creek-street-journal-sunday-28th-oct.html). Click on the photo to enlarge.

Gary

[GaryD]

Hi,

We freeze duckweed for later use by our Jade Perch. In the past, we've tended to use small plastic tubs and trays as moulds....creating small biscuits of duckweed.

We discovered that getting the frozen duckweed out of the moulds was frequently problematic so we've begun to use larger trays with sloping sides......we end up with one large "biscuit" which is easy to get out of the mould.

A couple of light taps with a hammer and the entire slab of duckweed is coverted to managable chunks of frozen fast food for fish.

GaryD

[DuncanC]

Hey Gary,

It looks like frozen chopped spinach :) I bet the fish love it! It's great to see options like these for fish feeding when away. It also looks like it would be a lot easier for a family member or temporary system keepr to just throw a 'chunk' in for the fish that possibly measuring fish food out and mixing in soy beans etc.

Cheers,

Duncan.

[GaryD]

Hi Duncan,

Frozen, chopped spinach or silver beet would also be a good greenfeed for omnivores.

Gary

[kenc45]

In the May Issue of the Practical Aquaponics Newsletter says that duckweed dies off at temps above 30 deg. Is this water temp, or air temp? Basically, I'm asking if I'd be able to grow it- as air temp up here is over 30 most days.

[GaryD]

Hi Ken,

I wrote that article and it refers to water temperatures.

There are many species of duckweed.....some of which are native to warm places. There's a nice little species called Wolffia that comes from around Cairns and that should be perfect for your purposes.

When you go to Darwin, do the rounds of the aquarium places and you're bound to find some local duckweed.

Gary

[gtpratt]

I am wondering if we have duck weed in our pond?

We bought a small bit of Azolla? from the local garden centre and it quickly grew to become a mat of large thick green stuff on the top of the pond. In winter it went red and is now starting to go green again?

Does this sound like the duck weed you guys refer to or is it something else?

Should I be harvesting this and attempting to keep the plants small.

I note the chooks dont seem to go wild trying to eat it.

I also have a problem of some kind of noxious weed in the pond I will be removing this and attempting to let the azolla take it over.

Any advice gratefully received.

Gra.

[GaryD]

Hi Graham,

Azolla and duckweed are two quite different plants.

The duckweed we have is tiny.....probably about 2mm in diameter.

Gary

[gtpratt]

Hi Graham,

Azolla and duckweed are two quite different plants.

The duckweed we have is tiny.....probably about 2mm in diameter.

Gary
Clearly I do not have duck weed.... Where can I get some? anybody wanna send me a cotton ball with water and a little duck weed on in a plastic bag?

Naturally I will ensure that the grow pond for the duck weed does not have external access for birds etc.

Kindest regards.

Gra.

[GaryD]

Hi,

A duckweed tank is an integral feature of our new 4 tank set up.

We used a 585 litre grow bed for the tank. It is connected to a 950 litre fish tank containing about fifty 75mm-100mm Jade perch fingerlings.

Bio-filtration is provided by a 235 litre grow bed filled with clay pebbles. Duckweed also assists with the maintenance of water quality in that, not only does it remove nitrates from the water, it will (unlike other plants) use ammonia in its un-ionised form.

A simple weir arrangement ensures that the water level in the duckweed tank remains constant and a bypass line on the pipework from the fish tank to the bio-filter ensures a slow, steady flow of nutrient rich water into the duckweed tank.

I've mounted a mini-greenhouse cover on the tank and this creates the hot and humid conditions favoured by the species of duckweed that we grow.

Photo 1 - the duckweed tank
Photo 2 - the weir arrangement that maintains the tank level. If we used the usual standpiple set up to maintain water level the duckweed would be sucked into the tank. The weir keeps the duckweed in the tank while allowing the water to return to the fish tank.
Photo 3 - fast food for fish.

Gary

[Dufflight]

The stuff I borrowed out of the local lagoon does not look like that. Will take a close up photo later and post the pic. Fish still eat it.

[GaryD]

Hi Duff,

The stuff you got from the local lagoon (not a practice I recommend) could be Azolla or even water hyacinth. Fish will eat both.

Then again, it might just be another form of duckweed. Photos will assist in its identification.

Gary

[Dufflight]

Got some pictures. The left seems to have a few different types or stages. And the left I like to call butt weed. Because it is growing in an outdoor ash tray. The left only had a few leaves a month ago.

[GaryD]

Hi Duff,

The one on the left is Azolla (fish eat that too) and the one on the right is duckweed.

Gary

[Dufflight]

Cool. They both came out of the same source. The duckweed must be the smaller bit in the left one. Might have to to a little separating to keep a better stock. Don't know what comes in cigs theses days but its like miracle grow. I wonder what tobacco is high in besides tar.:D Thanks for the ID.

[GaryD]

Hi,



Don't know what comes in cigs theses days.....

I think I read somewhere that about 4000 chemicals can be found in a cigarette......several of which are very deadly. Also you may find that the nutrients are coming from the smoker.

If you take a few of the duckweed plants out of the butt bucket (perhaps 20) and put them in a small tank of their own, their numbers will increase dramatically in a short time. If you put the tank in a similar location to that of the butt bucket (but without the smoker), you'll be right.

If you can replicate the conditions that I have in my duckweed tank, you'll find that it grows like a ....well a weed.

Gary