The Amazing Duckweed Filter.

[Mike_Noren]

An interesting plant I'd like to try again is Lemna trisulca, the Star Duckweed.
It's bigger and doesn't float, but instead form a loose submerged lattice somewhat reminiscent of an aquatic moss. I think it might be good as shelter for fish larvae, but it also grows almost as fast as Common Duckweed and so might also be useful as a nitrate filter.

[exasperatus2002]

I would love to get some for my pond for my goldfish. But I havent found any around me. I use hornwort in my malawi tank as a floating plant.

[Xod]

does anyone know what kind of duckweed is this?

[apistomaster]

Not Duckweed but Salvinia unless it is Limnobium. Hard for me to tell them apart.
Either way, a much better and more welcome plant than Duckweed. These are easy to control, can grow fast and make an excellent floating cover plant. Their root systems provide excellent cover for the small fry of some fish. If it grows well for you it is able to soak up a lot of nitrates.
I used to have a lot of a Salvinia species for several years but some how I allowed it to disappear.
Sometimes a plant only begins to thrive when it is kept in fairly dense quantities and if thinned too much it can be easy to loose the species by not allowing sufficient amounts to allow for any setbacks. I wouldn't mind getting it back again.

[Bas Pels]

I'm quite certain it is Limnobium. This plant has a little sponge under it's leaves, and it does hats water on it's top. I think it is the most beautiful floating plant, but not the easiest one

The picture does, however, show 2 species, the Limnobium is shiny, the other plant, a bit greyish, is Pistia stratoites, not very well developed. Again a very usable floating plant, which does help keeping the water usable.

In my experience Pistia grows much faster then Limnobium does

[Xod]

glad to finally know what it is now. This plant has grown so much that it multiplied 3x in about 2months. eats up green water and the roots look so cool! the fish do like to pick and eat it when it gets too long which is free yard work! I highly recommend this to any one looking for floating plants

[dw1305]

Hi all,
Definitely Limnobium.

Almost a year after my first post and I still love duck weed, L. minor.

I like Lemna as well, L. minor is easily controllable, because it's growth response to nitrogen is almost linear, if you can reduce the total N in your system, you can reduce or eliminate the Lemna minor, the Fat Duskweed (Lemna gibba) thrives in even more eutrophic conditions and is also a lot chunkier, there is also Spirodela polyrrhiza if you want a bigger alternative.

A lot of research has been done into Lemna. Have a look here:
http://www.dcm.nt.gov.au/__data/assets/ ... 43/14e.pdf

cheers Darrel

[corywink]

does anyone know what kind of duckweed is this?

Looks like what's commonly called frogbit. I use them in my tanks. They spread fast and I have to throw out handfuls during weekly water changes, but they are easy to control because of their larger size. They even flower in my tanks but the flower is rather dull lol. Yeah when I kept blue rams they would beat the roots and kept them from growing too long

[thijs]

Lately both my Limnobium and my Lemna started to grow slow. I used to remove loads of these every week. Now I only need to remove them every few weeks. Does this mean my N is decreased, or are there other possible causes (and is my duckweed filter defunct)? Limnobium and Lemna are my only plants.

[MatsP]

It certainly means that SOMETHING they need to grow has reduced. It is much harder to say whether it is nitrate, phosphate, potassium [aka NPK - they are the usual chemicals in "fertilizer"] or some micronutrient.

--
Mats

[dw1305]

Hi all,

Lately both my Limnobium and my Lemna started to grow slow. I used to remove loads of these every week. Now I only need to remove them every few weeks. Does this mean my N is decreased, or are there other possible causes (and is my duckweed filter defunct)? Limnobium and Lemna are my only plants.

As suggested something is limiting plant growth, nitrogen (N) or potassium (K) would be the most likely options. I'd try adding a small amount of KN03 (enough to give 5 ppm N) and you should see a greening of the plants and increased growth if either K or N are deficient. If there is no improvement it is one of the other nutrients (probably P or Mg).

I like to keep low nutrient levels in my soft water planted tanks and I use a conductivity meter and the colour/growth of Limnobium and Lemna as indices of this. If I have small, slow growing, pale green floating plants and a conductivity of about 100 microS, I know water conditions are pretty good.

cheers Darrel

[Bas Pels]

Other nutrients can also play a role.

I once heard somewhere in Australia the soil os deficient in copper. no crop would grow there. Adding 1 gram of coppersulphate per hactare (that is 10.000 square meters) could solve this

plantgrowth is quite complicated, sometimes, and changing water is so easy

[sidguppy]

one of my smaller tanks has enormous growth in duckweed

I tried introducing it again in my big tank, hoping that this time it would establish itself and eat up the nitrates.
I dumped in a huge load, compesed of mainly duckweed, some Hydrilla and some Pistia. all invasive species

my Madagascarian cichlids cleaned up every single bit of green within 48 hours and I duped in at least 2 pounds of live veggie matter.....

[thijs]

Thanx,
As a plant ecologist I should know. But history learned me to value practical expertise. Especially Darrels remarks are useful. Especially the Lemna are very yellowish, maybe I should do a conductivity test.

Too bad an aquarium good for the fishes results in such ugly yellowish plants....

[Mike_Noren]

Especially the Lemna are very yellowish

I'd say likely iron deficiency. Lemna are enormous "iron hogs" and will quickly deplete all available iron. You could try a fertilizer rich in iron, e.g. Tropica Mastergrow.

[2wheelsx2]

It's cheaper just to buy bulk chelated iron (DPTA) and add that. Tropica Plant Nutrition (that's what Master Grow is called now) is $$, at least on this side of the pond.

[dw1305]

Hi all,
Has the addition of KNO3 greened the plants up? if it hasn't

It's cheaper just to buy bulk chelated iron (DPTA) and add that

sounds a good idea and I'd probably suggest that as well. You need to oxidise the iron chelate solution, I usually just do it with an air/pump stone, and either don't store the stock solution, or store it in the dark. The reason for this is that the chelate is degraded by light releasing the Fe2+ ions, making them both available to the plant (good) and to form other compounds (not so good). I think DPTA is more stable than EDTA, but I'd need to check.

I might also add a small amount of Epsom salts (MgSO4.7H2O) as magnesium is the central atom of the chlorophyll molecule and Mg induced chlorosis is very similar to Iron chlorosis.

cheers Darrel

[Jools]

If you run a fishroom and regularly trade with other similar folks, or buy from auctions, you'll end up with duckweed. On balance I think it's more of a pest than an aide, but I certainly wouldn't wish it into extinction and it can be useful for me. My vain discus like it and it is very easy to harvest from their placid tank and feed to my barbs. Many barbs will eat it, as will mollies, hoplos (

Megalechis

), several species of

Synodontis

eat it too and some other things like Semiprochilodus and Metynnis. Surprisingly,

Ancistrus

don't eat it. It's really only the cats (so far) that I've found that eat it and do not eat less invasive ("proper aquarium") plants. By far the most effective eradication tool for me is water current.

So, duck weed is a great name. It floats like a duck and is a weed.

Actually, my big barb tank gets this as a regular food twice a week now and there is not a blade of it left after 24 hours.

For me, it's a tool. I have added it to tanks that I am feeding heavily and I want some shade, I just net as much as I can every now and again and feed it to the barbs or compost it. Trick is to make it work for you, as you will go insane trying to eradicate it.

Jools

[mummymonkey]

Put me firmly in the "hate" camp. It seems to appear from nowhere and it coats your arm if you put it in the water. Yeuch! It's like Marmite I suppose.

[Hellspawn]

My Guppys love it. The juvies are hiding underneath the leaves and between the tiny roots. I got the duckweed plague from a local pet store when I bought some aquarium plants. Promblem I have when scooping it out with the fishnet is guppys trapped in the net. So I need to be carefull if I don't want accidental scooping casualties in my fish population. I just throw the duckweed in the trash.