Name: Lemna sp.
Has to be the easiest plant I've ever grown. I started off with one tiny piece that hitch-hiked with a new tank member...pretty soon covered my entire tank surface. I got rid of it because it produces a very strong musty odor, and was shading my main plants way too much.
I have duckweed in both tanks and outside in the pond. The baby angels love to eat this stuff so it is a good veggie for the growing kids. I have noticed that the outside Duckweed has much longer roots @ 5 cm, compared to the tank stuff that has about 0.5 cm roots. Not sure why though. It grows like mad, no CO2 needed so it can get out of hand easily. I have taken out buckets of the stuff even with it being eaten all the time. Still love it though.
I originally had just a few small duckweeds. They soon spiralled out of control, and there were hundreds of them, with dozens of plantlets popping up daily. I now don't have any duckweed in any of my tanks. All I have is a wad of it in a bowl I've yet to throw out. Even without lights, the plants have survived several months without losing colour in them, along with some Java moss. I wouldn't suggest this prolific, immortal plant, as it clogs filters, and it should only be taken if you're willing to deal with scooping up cupfulls of it and unplugging your filter daily.
Duckweed is a good plant if you don't have a top over your tank blocking the beauty of their lush leaves. They are very pretty when you can see the roots grow and hang down. Any small fish that stay close to the surface will love to swim through the roots. Do not get this plant if you have big fish because whenever that fish eats it will devour the duckweed. Otherwise it's a fun plant to have.
When I first acquired this plant, I thought it was cool. No, it grows too quickly. After two weeks, it covered the top of my 200 L planted tank. Steer clear.
Duckweed is an uncontrolable species of plant that I recommend be avoided. What starts off as a little punnet of floating weed that the pet shop guru sells you won't stay this way for very long. Within 2 or 3 weeks it will have entirely taken over your tank or pond. Overall this is a very high maintenance plant, useful for not much at all.
All of the above comments about duckweed are perfectly true. Having said that, however, I have this to add. Do you need to control nitrogen levels? Do you have fry that need a place to hide? Do you need a you proof plant? Need a way to control algae? Then duckweed is the aquatic plant for you! Every handful you scoop out is that much more nitrogen removed from your tank. Scoop it out, compost it, and move on. As long as you leave a few plants in the tank, it'll reproduce. You can think of duckweed as the plant equivalent of guppies...just add water!
I have to agree with Matt Grahams' last comments on this lovely little plant. It apparently used to be a rule of thumb, in days gone by, amongst aquatic gardeners that if you grew Lemna sp. in your tank, then this was an indication that your water quality was good. But the situation here is reversed really - it is having Lemna sp. growing in your aquarium that makes your water quality 'good' for fish! If you can put up with having to remove some Lemna sp. (eg. leave 30% to 40% cover) from the surface of the water from time to time, so that plants below the water surface can get some light, then you are good to go. Yes, it can be a bit messy if you have to get your arms in the tank and "adjust the scenery" or whatever, and you pull your arm out covered in this sticky little weed, but what the hey - that's you removing some already!
I have had duckweed before, and I really think it is a nice looking plant, but it can be a big pain. It will cover the tank surface fast, blocking out light and getting into your filter. Up side is fish LOVE to eat it. Koi and goldfish seem to love it the most, the oscars like it too. My biggest problem with it was that after having my hands and arms in the tank the duckweed would make me itch badly.
I once used this in my guppy tank because I was fed up with seeing all my guppy fry cannibalised. This has been the best fry friendly plant I've ever used, even riccia and Java moss/ferns were put to shame by this little plant. The only problem you have once you've got it is getting rid of it. After I finished with the guppy tank I removed what I thought was all of the duckweed, as well as leaving the heater on a shelf for 2 months with dead, dried up duckweed on. When I put the heater in a brand new tank I ended up with it growing again. It's now been 5 months and I still find a few new leaves appear every few weeks.
I have had this plant for about 4-5 years since when I worked at a pet shop and recognized what it was in a batch of new plants, one of the plants that is very good at hitchhiking. This plant grows by getting 4 leaves then splitting into two plants. I found this out when I put a single 3 leaf piece of duckweed into a bucket under a porch, and every day it grew an extra leaf, so the first day it had 4, and the second day it split into two, and by the third day the first plant had 4 leaves again and the new plant had 3 leaves. It may be illegal where you live to let it get into the waterways or to even let any get into your sink. A fun plant, but it does grow too fast for most people to handle.
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