# Is duckweed the answer?



## jlm9679 (Jun 26, 2009)

Still on the subject of setting up a new El Natural tank, it strikes me that an abundance of floating plants - duckweek, water lettuce, etc... - may be the soultion to a dead-easy maintenance aquarim setup: given sufficient quantity, to the point of totally covering the water surface of the tank, would they alone provide enough oxigen for a few fish, and would they consume enough nutrients to defeat any algae growth?

Then one could concentrate on rock-scaping the bottom of the tank.

Floating plants enjoy maximum light and co2, require no substratum and generally are quite beneficial to the tank's ecosystem.

I can think of two possible scenarios:

1 - Floating plants alone covering 100% of the water surface, ie no plants of any other sort, with or without substratum.

2 - Dividing the tank in two parts, the first area as in 1 above (only floating plants), the second with the usual set up: substratum and rooted/anchored plants.

I would be interested to know if this setup can work, as an alternative in case things go wrong with the usual planted aquarim.


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## davemonkey (Mar 29, 2008)

Certain floating plants would work (those with big appetites). Water Hyacinth is one floating plant that could do the job . It has been used in some water treatment facilities to clean waste water. Red-root floater would work better than duckweed (I only assume this) because it has a larger root system, and water lettuce and frog-bit as well.

I do think that if you had a cover of floating plants they would take up many nutrients, but you then have to find the balance of how many fish would provide their nutrition without providing too much.

-Dave


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## StevenLeeds (Jul 21, 2007)

This sounds like my old turtle tank. I had a stinkpot in a 20 long. Filter sand for substrate and rock. The top of the tank was completely covered with duckweed, salvinia and frogbit. They grew really really fast.

Filter was a zoomed 501 and the light was (2) 26 watt spiral CFL in a cheap 10 gallon hood.

The ones that didn't do well were red root floaters, and water lettuce. I think the air out here is too dry.


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## dwalstad (Apr 14, 2006)

jlm9679 said:


> Still on the subject of setting up a new El Natural tank, it strikes me that an abundance of floating plants - duckweek, water lettuce, etc... - may be the soultion to a dead-easy maintenance aquarim setup: given sufficient quantity, to the point of totally covering the water surface of the tank, would they alone provide enough oxigen for a few fish, and would they consume enough nutrients to defeat any algae growth?
> 
> 1 - Floating plants alone covering 100% of the water surface, ie no plants of any other sort, with or without substratum.
> 
> 2 - Dividing the tank in two parts, the first area as in 1 above (only floating plants), the second with the usual set up: substratum and rooted/anchored plants.


Floating plants don't provide water with much oxygen. In fact, ponds with a dense floating plant cover have been shown to have very little oxygen (see footnote, p. 148 of my book). Most of the oxygen produced by photosynthesis goes right up into the air-- not the water.

Most people that use the "Aerial Advantage" do so by having a separate planted receptacle with emergent and floating plants. For example, a mini pond (connected to a large unplanted Koi pond) takes in polluted water and purifies it. Water is returned to the main pond via a nice aerating waterfall.

Some aquarium hobbyists use planted refugiums or sump tanks connected to the main tanks to purify their fish tanks.

Your idea of dividing up a single tank uses the same concept. It might work fine, but I'll be curious to see how you do it.


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## wkndracer (Mar 23, 2008)

I'm harvesting the duck weed using it to pull any leaching 'extras' out of the water column. Granted this is my first 'dirt' tank but stem plants seem to be what keeps a new soil sub stable. When / where I had gassing issues was when the stems were having issues (not growing). The duck weed has kept me from having algae issues I think but every time the mass increases to 50% coverage its discarded back to a single corner.


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## jlm9679 (Jun 26, 2009)

dwalstad said:


> Floating plants don't provide water with much oxygen. In fact, ponds with a dense floating plant cover have been shown to have very little oxygen (see footnote, p. 148 of my book). Most of the oxygen produced by photosynthesis goes right up into the air-- not the water.
> 
> Most people that use the "Aerial Advantage" do so by having a separate planted receptacle with emergent and floating plants. For example, a mini pond (connected to a large unplanted Koi pond) takes in polluted water and purifies it. Water is returned to the main pond via a nice aerating waterfall.
> 
> ...


Thanks for the tip about the insufficient oxygenation from floating plants, it's just what I needed to know to make a decision about their viability.

I'm coming round to the conclusion that a duckweed-only tank isn't practicable (not enough oxigenation both in the substrate and in the water column being the main reason), but considering that it usually is a very helpful addition to an El Natural setup it seems that a divided aquarium into separate duckweed and planted areas is probably the best option from the ease of maintenance and health of the ecological biosystem point of view. The division could be a simple bit of plastic or glass attached to the tank walls, perhaps a couple of cm deep (1/3 of an inch), splitting the surface in two areas, say, 50-50 - would this be about right?

I know that usually floating plants are left to drift on the surface, which may be detrimental to whichever plant they happen to sit over. Hence the advantage of keeping them to a specific part of the tank. Or maybe not...

Now, the question of the substrate would need some attention since about half of it would not have the oxigenation provided by plants - ie it would have no planted biomass at all, and little light. The solution would be to put substratum fertilizer ONLY in the half that is going to accommodate the plants, and only gravel (or sand, or nothing, for that matter) in the other half. The result would be half a tank with planted foliage under decent light, and the other half in the shade, under the duckweed and with no plants growing from the soil, thus providing the benefits of oxygenation and protection against algae (hopefully ray.

Just one more question: is sunlight really essential in an El Natural system? We have little of it over here (London) in winter, and it is said to encourage algae. Would this sort of setup work mostly with artificial light? I was hoping to place the new tank in a corner sheltered from direct sunlight, but receiving plenty of reflected natural light - when there is some!


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## jlm9679 (Jun 26, 2009)

wkndracer said:


> The duck weed has kept me from having algae issues I think but every time the mass increases to 50% coverage its discarded back to a single corner.


I would have thought that getting rid of a lot of duckweed at once may upset the balance in the tank. Didn't you notice any adverse effects after those clean-ups? After all you get a lot extra light all of a sudden, not to mention a decrease in nutritrient absorption by the plant mass...


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## bartoli (May 8, 2006)

jlm9679 said:


> it seems that a divided aquarium into separate duckweed and planted areas is probably the best option


If your tank has enough head room, you may want to try Water Hyacinth as suggested by davemonkey. Water Hyacinth is easier to manage than duck weed and sucks up much more nutrients than other floating plants. In most of my tanks, I have at least one Water Hyacinth. Java fern does not seem to be bothered by having a Water Hyacinth right on top of it. Of course, if there are two or three Water Hyacinth on top, the light blockage would be too much.


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## Alex123 (Jul 3, 2008)

First duckweed is not the answer. Duckweed alone can not keep the aquarium clean of pollutants. You have to keep in mind the amount of nutrients a plant absorbs is directly proportional the bio mass produced. Duckweeds are flimsy and small. Even a tank totally covered by Duckweeds will not a whole lot of bio mass. Now Water Hyacinth grow pretty large and grow fast thus more bio mass thus more cleaning power. 

Separating the tank and logistic of the substrate seems a little cumbersome and actually not good look for an aquarium. You are better off having 50% Duckweed coverage and reduce it to 25% and cycle through that process. This will allow most of the light to penetrate and since it floats around, there will be even distribution of light in the tank. With that said, if you have plants in your tank, removing a large portion of the duckweed is not going to throw off the aquarium too much. I have a lots of plants and when I let my duckweed in my tank reach 100% coverage(I'm lazy) I have cut it to 10% and had no issues.


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## wkndracer (Mar 23, 2008)

The only thing if at all I've seen after culling the floaters is a small increase in stem sprouts if anything at all. Phosphate levels are the only problem I've had thus far and a water change is easy to do. My soil is still green. (couple months old)


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## EMc/ (Feb 20, 2006)

Duckweed is also used in some water treatment facilities to clean waste water.
LINK

Here's another scenario. Floating plants throughout the tank. I successfully have kept tanks w/ only floating plants like najas grass, hornwort, & duckweed. You can add java moss, java fern, & anubias down low to add more interest. None of these need a substrate & all are easy to grow. The only thing you'll need to do is keep the floating plants thinned, as they grow prolifically.

I don't find these tanks as interesting to look at (as tanks w/ plants that have rooted plants, too), but easy they are.


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