The Amazing Duckweed Filter.

[AlaskanCorydoras]

If you are anything like me, you're a bit fanatic about the quality of your water. Having had a PH crash 6 months ago, I've been very vigilant to keep it from happening again. (In retrospect, I suspect that my PH crash was caused by me disturbing a large anarobic bacteria colony, releasing nastiness into the water.)

One of the tools that I've found surprisingly useful is an innocuous little plant, duckweed. Duckweed is one of the smallest flowering plants, is surprisingly high in protein, and grows EXTREMELY quickly. The doubling time on my tanks is between 3-5 days. It floats on the top of your water, and sucks up ammonia and nitrate, as well as other toxins in the water. Duckweed is nice in that it will outcompete many unsightly algaes, and thus having some on the surface of your tank can be extremely beneficial. Further, many fish species enjoy nibbling on duckweed, and benefit from the added shade and plant matter in the tank.

The trickiest part about growing duckweed is keeping it out of your filter. The trick that I use in my tanks is to use a "floating feeder" at the downflow of my powerfilter. This keeps the powerfilter from pulling the duckweed down, and it won't sink otherwise. You can also use simple airline tubing and suction cups, if you wish a cheaper (or more customizeable) barrier.

Then you just leave it alone. It sits, it reproduces and filters toxins out of the water. When you have enough, you throw most of it out, ridding yourself of much of the potentially hazardous fish wastes. If you run the larger surface area tanks, it is possible to essentially eliminate Nitrate with this method.

But don't take my word for it. . . read more here: http://www.mobot.org/jwcross/duckweed/duckweed.htm

[L number Banana]

Some people hate it but I loooovvee duckweed You can keep an emergency supply in a little glass on the window sill for those new tank green water blooms. I also use it to clear my pond in the spring when the first algae bloom appears. Poof! gone, and you can use a shop vac to suck it all back up if you don't like it in your pond. Just use the flat nozzle against the surface.

And as someone stated in another post,

Megalechis thoracata

eat it!

[Mike_Noren]

There's apparently some 70 species of duckweed, but the only ones I've tried are Lemna trisulca and Lemna minor.
Lemna minor is among the worst weeds I've ever had in aquaria, comparable only to Caulerpa in marine aquaria. It's almost impossible to eradicate and form thick mats over the surface of the tank, hindering light and gas exchange, and out-competing all submerged and many floating aquarium plants for nutrients.
I don't think I'd intentionally use L. minor in any planted aquarium, there are other fast-growing floating plants, such as Salvinia, Pistia or Ceratopteris, which are easy to control and as a bonus provide some shelter to young fish.

However, L. minor does grow insanely fast, so if you have a problem keeping nitrates down then it'll certainly help with that.

[sidguppy]

I wish I could get a plague here......same with MTS

unfortunately I have fish thaty eat both MTS and duckweed with loads....

last I was so desperate to feed em that I threw a handful of MTS in the main tank; those were destroyed and eaten within 24 hours.

duckweed and filamentous algae I got rampaging in one of my smaller tanks.
everytime I have a surplus I dump a load in my main tank and for the next few days my fish in there lay green turds

the downside of all the fun is that any other plant gets eaten as well. even javaferns or anubias. it's all just grazing.

[AlaskanCorydoras]

Funny you mention the MTS. That is actually my second tip.

Malaysian Trumpet Snails are good at reducing the "Bad bubbles" to quote L Number Banana. They help stir up the substrate, and avoid the anaerobic bacteria that produce the tank-killing hydrogen sulphide.

If MTS aren't really your thing, you can get burrowing aquarium fish. Kuhli loaches and Horseface Loaches both burrow in the substrate, and can help aerate it. Now I don't have any horsefaces (They can get kinda big. 8") but I do have some Kuhlies. I rarely see them they enjoy burrowing so much. (And they max out a 4" and are terribly skinny in the first place.)

If you have thick substrate, the MTS or burrowing fishes are quite useful.

[bronzefry]

I used to view duckweed as a scourge. But, when I noticed the water quality in a few of the tanks improving, I was not so anxious to get rid of it(not that I could ). I've had Otocinclus spp. and Corydoras spp. grazing at the top of the tank, eating whatever collects on the duckweed. I now put it in fry tanks, especially with Ancistrus sp. I've noticed they actually eat it. The one drawback I had with it was an overgrowth and one of the tanks overheating. This happened last summer, even when I had the heater unplugged.
Amanda

[shamrock]

http://www.guppies.com/forums/showthrea ... 18686.html

not sure whether all stated is actually true, but sounds good! is there any possibility of trapping the duckweed? could use some for of a membranous compartment so it is stuck somewhere without spreading? but i guess that would be impssible?

[2wheelsx2]

Unless you like the look and like having it stuck everywhere, don't do it. I hate it. I got it from someone who sold me some shrimps and I have not been able to eradicate it in my planted tanks. What a nuisance. Get some other plants like water sprite instead. Better nitrate sinks and easy to get rid of or sell off.

[corywink]

I use frogbit instead, it's much larger than duckweed so you can control it no problem and it doesn't get stuck in your fitler or tank decorations.

[apistomaster]

If you have managed to avoid introducing any duckweed so far do not introduce it now!
If you ever wanted to try a fresh water refugium component to a wet/dry filter the plant I recommemd is Najas guadelupensis. It grows extremely fast and with enough lighting it can fill all the available space. It grows very well natantly and any excess is easily removed. The rapid growth it is capable of makes it a very useful plant to use up excess nitrates. This is the best suited plant for for a fresh water refugium I know of. The concept is intellectually appealing but in order for it to work well you need to use large ponds. Water restrictions and price increases made these natural water remediation pools almost standard for the commercial breeders of tropical fish in Singapore. But these are much or complex ecosystems which use many bog plants, the energy to drive them is free sun light and they have aenaerobic zones where denirifying bacteria use nitrates as part of their food source and unlike our familiar nitrification biological filtering system upon which rely and are most familiar with, denitrifying bacteria are able to complete the cycle by consuming nitrates and just as photosynthesizing organisms use sun light and sugars in their metabolism and release O2 as waste, the anaerobic denitrifiers use nitrates and another chemical energy source to convert nitrates into N2 gas which leaves the water and enters the atmosphere. This the missing part of the complete nitrogen cycle in fresh water aquariums.
This process doesn't work well enough in small fresh water closed aquatic systems to be used to much effect. It can and is used in reef tank filter systems but it requires expensive technology and good understanding of the process. Many reef keepers are accustomed to buying and using much more expensive technology than is commonly used in hobbyist level fresh water systems.


Ceratophyllum demersum is my next choice. It is Tropical Hornwort.

Water Sprite and Brazilian Pennywort are both excellent plants but their growth habits do not allow for as efficient use in a refugium stage in the filter. Use them in the display tank.

You should consider a planted tank stage in a filter system more of an experiment and not have high expectations. Only water changes truly make significant reductions of nitrates very useful and practical. These plants are better used in the main tank and used as both decorative yet functional additions.

[shamrock]

but is there no way of confining the duckweed? or do you think they'll just be able to escape out and overload the tank anyway?

thanks

[MatsP]

I would suggest that duckweed is a "bad" thing in a tank. Yes, it grows quickly and takes up a lot of nitrate, but there are, as suggested, plenty of other plants that are easier to control and do a similarly good job in soaking up nutrients in the water. I have frogbit in some of my tanks, and it works well.

--
Mats

[Mike_Noren]

It's tiny and clingy and sticks to everything you put in the aquarium, it's not very buoyant so water current can submerge it under floating obstacles, and it's a flowering plant which sets tiny sinking seeds - in short, while I suppose it's theoretically possible to contain, it's in practice difficult.

[andywoolloo]

I like the duckweed but it is hard to contain. I use airling tubing in a circle attached with a , on eof those, safe valve things? check valve? so it floats in a circle and i put the duck weed in there, but most of my tanks have too much flow/action so it gets all over.

I just put it in my goldfish tank now, they chow on it. And in my betta tanks, there tank has less flow obviously and it grows nicely and shady or them and then I take it out every so often and feed the goldfish with it

I also love the MTS s , as all my tanks have sand.

[shamrock]

what do you do to keep your MTS in check? don't you find they "take over" the tank and cause trouble? i hear they even get into filtration...

[apistomaster]

what do you do to keep your MTS in check? don't you find they "take over" the tank and cause trouble? i hear they even get into filtration...

I have to periodically remove the impeller from my two Eheim Classic #2217 because very small MTS become caught up in the impeller enough to slow it down and sometimes even lock it up. They are OK in their place but it is difficult to control their numbers. Even constant trapping them on food under a dish doesn't really make much of a dent in their populations. I stopped trying but I still would like to try using Assassin Snails to see if I can get back some control over their populations. I have one tank where they do not thrive but they do hang on. It is a 20 Long which is set up for Parotocinclus cf. epplyei and Black Darter Tetras, Poeciliocharax weitzmani. The tank is kept at a pH of 4.0 to 4.5 and I use straight RO water. In use, the actual TDS rises some to about 15 ppm. The low pH and lack of minerals makes it a little harder for snails to obtain and retain enough calcium for shell growth. Many have white areas as if the acidic water is etching their shells. Pond snails also manage to survive but their shells are paper thin compared to those raised in more normal water chemistry.

Gold Fish and maybe Koi are among the few fish which will eat Duckweed. It really is a pest plant with few redeeming values. I am constantly at war with it but it is extremely difficult to eliminate and is very easily spread to other tanks.
I wish it did not exist.

[2wheelsx2]

Silver Dollars will also eat duckweed, but the problem is, like goldfish, that they will eat all your other plants you want to keep too. I had 4 silver dollars in my 125 and as juvies they keep it totally clear, but got too crazy for the tank and I gave them away, so now the duckweed is starting to come back (every single little piece can bring it back with a vengeance).

[apistomaster]

Silver Dollars are so frenetically paced fish and grow so large that there are only certain kinds of set ups where they fit in. Certainly not any planted tank nor with the wild Discus I keep.

[L number Banana]

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

In my main tank, the flow is too slow to suck in any but the output sort of lands on the tiny plants and sends them down a couple inches where they float back up looking like little green jellyfish. They don't get stuck anywhere else so maybe it's ony a good plant for low-flow tanks. When the surface gets covered, I scoop out a couple nets full and add them to my outdoor pond for the gold fish. The coverage they provide in my tank allows my glass catfish to feel safe and allows enough light to penetrate to keep my substrate plants happy.
If it makes you uneasy after reading others experience, you could try things from the lily family, they will send up leaves that float on the top and give you flowers once in a while too!

Some of the pond people use 'filters' of plain grocery store watercress to clean the waste. For a fish tank nitrate vacuum, simply grow it in a basket hooked to the side of your tank and take it out when you've found the reason for the high nitrate levels.

[shamrock]

hey

looks like it works great for you you have a good system going it looks like

good luck! i may give it a go, but in isolation

[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