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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

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

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.....

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....

thijs wrote: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.

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.

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

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 (), several species of eat it too and some other things like Semiprochilodus and Metynnis. Surprisingly, 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

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.

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.