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HOB plant filters


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#1 mywan

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Posted 20 January 2011 - 08:46 AM

Based on studies from industrial sized constructed wetlands for wastewater treatment it occurred to me a downscaled version might be useful as a HOB aquarium filter. Recent discussions here prompted me to actually run some numbers. To run these numbers I chose Water Hyacinth (Eichhornia crassipes), which has the disadvantage of being an invasive and restricted in some states. The idea is to numerically demonstrate the feasibility though, rather than restrict the concept to a particular plant species or monoculture.

The idea of a HOB plant filter for the aquarium in principle has many advantages.
1: They can be precycled (matured), before being placed on the back of an aquarium.
2: They are not dependent on dissolved CO2 levels in the water, allowing additional aquarium plants without interference.
3: The lighting requirements are somewhat reduced for exposed plants.
4: It provides a habitat for scud colonies or similar food stock.
5: The increased surface area and oxygen in the root system provides for better gas absorption in the water.
6: The root system provides mechanical filtration.
7: The symbiotic nitrosomonas and nitrobacter bacteria in the root system provides standard biofiltration.
8: The plants metabolize nitrates not achieved through standard biofilters.
9: It greatly reduces the need for water changes.
10: It can provide for the phytoremediation of heavy metals.  

The primary concern is whether an effective filter can be produced in a sufficiently small area behind the aquarium. For area requirements I will assume a 12" inch extension on the back of various standardized aquarium sizes the length of the aquarium. On www.oas.org it gives the effluent treatment rate for hyacinth as "approximately 1 m2/m3/day of water to be treated". Converting this to a ft^2, for the overhang behind the aquarium, we get 1 ft^2 cleans 80.5 gallons/day. The effectiveness of treatment, using four different unspecified larger scale models, is given in the above link as:

Source Reduction --- BOD ---- COD - TSS - N --- P
Raw wastewater ----- 97% ---- n/a - 75% - 92% - 60%
Secondary effluent - 83% ---- 61% - 83% - 72% - 31%
Secondary effluent - 35% ---- n/a - n/a - 44% - 74%
Secondary effluent - 60-79% - n/a - 71% - 47% - 11%
Source: U.S. Environmental Protection Agency, Innovative and Alternative Technology Assessment Manual, Washington, D.C., 1976, (Report No. EPA-430/9-78-009). As provided on oas.org link.

Aquarium water is best described as a "secondary effluent". Here BOD is Biochemical Oxygen Demand, COD is Chemical Oxygen Demand, and TSS is Total Suspended Solids, N is Nitrogen, and P is Phosphorus. Reduction effectiveness is variable, and depends a lot on initial concentrations. So my idealized reduction rates, to be calculated, at various averages is only an indicator. Of course aquarium filters only need to keep up with a specific bioload, rather than improve a particularly bad source effluent.

Since the HOB plant filter is always considered the length of the aquarium the gallons of a 12 inch length section of a particular relative to a 12^2 inch plant ray is all that is needed to determine cleaning cycles/day. For a standard 10 gallon the width and height is:

Standard 10 gallon aquarium;
10" x 12" x (12") = 6.23 gallons
That same 12" x 12" hyacinth tray will process 80.5 gallons/day with one cleaning cycle/day.
Thus a hyacinth tray 12" inches x width of 10 gallon aquarium will provide 12.9 cleaning cycles/day.
With a 50% average reduction per cleaning cycle times 12 cycles is a 99.98% relative reduction/day.
With a 10% average reduction per cleaning cycle times 12 cycles is a 71.76% relative reduction/day.

The indication is, based on various sources, is that reduction efficiency goes down as the target effluent decreases. But once the target levels are reached there is no need for reduction. An aquarium filter only needs to maintain enough filtering capacity for the bioload provided. As the width and height of an aquarium increases the cleaning cycles per day is reduced. This would give shallower breeder tanks an advantage. Hence a 55 gallon aquarium, (48") x 13" x 21", comes to:

Standard 55 gallon aquarium;
13" x 21" x (12") = 14.18 gallons
Thus a hyacinth tray 12" inches x width of aquarium will provide 5.67 cleaning cycles/day.
With a 50% average reduction per cleaning cycle times 5 cycles is a 96.9% relative reduction/day.
With a 10% average reduction per cleaning cycle times 5 cycles is a 41% relative reduction/day.

This shows that such filters are, at least in principle, feasible. Obviously test need to be done with actual aquariums involving more than just monoculture plant species. In principles the controllability of variables is superior to larger outdoor systems, offering the potential for greater efficiencies. Experimenting with plant mixtures is also warranted. Mixing irises and other bog plants that doesn't significantly interfere with the hyacinth growing space or enhance effectiveness could add significant utility and beauty. Some other things that could be done is fertilizer ports added such that the fertilizer goes directly to the bottom roots, preventing it access to the main aquarium. This would increase overall efficiency, as efficiency tends to go up as nutrients are increased. Three sided models would also greatly increase the total filtration capacity.

The phytoremediation of heavy metals and rates is documented by many sources. Water hyacinth is not particularly unique in this respect, but here are some basic references showing this effect with hyacinth.

Cadmium, lead, copper, zinc, and nickel remediation experiments (pdf); http://www.apms.org/...ol42/v42p60.pdf
Mercury remediation; http://www.informawo...96~frm=abslink"
Zinc and Chromium remediation (pdf); http://www.bscw.ihe....001/Gakwavu.pdf

It may even be possible to dump contaminated water (sewage) in the aquarium and given enough cycling time be well suited for fish. I think this is a worthwhile filtering approach to pursue. What do you think of growing a swamp around your aquarium instead of in it, or in addition to internal plants?

Edited by mywan, 20 January 2011 - 08:48 AM.


#2 Erica Lyons

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Posted 20 January 2011 - 11:37 AM

View Postmywan, on 20 January 2011 - 08:46 AM, said:

What do you think of growing a swamp around your aquarium instead of in it, or in addition to internal plants?
It's an excellent idea, and actually, plant filtration is how the first fish tanks were run before electric filters were invented.  People would get a big ceramic basin, fill it with plants, and stick a couple fish in.  It was the only way, at the time, to keep fish as pets indoors.  

I really hope you go through and build this because I think it would be beautiful.  
Here is a picture of a neat paludarium:  http://showcase.aquatic-gardeners.org/2008.cgi?&op=showcase&category=3&vol=-1&id=154  If you ran a trickle of water down the back wall, it would be cleaner by the time it reached the bottom.

Edited by EricaWieser, 20 January 2011 - 11:38 AM.


#3 exasperatus2002

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Posted 20 January 2011 - 12:56 PM

View PostEricaWieser, on 20 January 2011 - 11:37 AM, said:

It's an excellent idea, and actually, plant filtration is how the first fish tanks were run before electric filters were invented.  People would get a big ceramic basin, fill it with plants, and stick a couple fish in.  It was the only way, at the time, to keep fish as pets indoors.  

I really hope you go through and build this because I think it would be beautiful.  
Here is a picture of a neat paludarium:  http://showcase.aquatic-gardeners.org/2008.cgi?&op=showcase&category=3&vol=-1&id=154  If you ran a trickle of water down the back wall, it would be cleaner by the time it reached the bottom.

an alternate pond filtration method is similar to what your proposing. Its a bog filter. You have the pump enter water at the base of a vessel usually filter with gravel with bog plants growing in it and the water is filtered on the way up to the surface of the vessel where it returns to the pond. Your making a freshwater refugium. Saltwater tanks use cauplera (a macroalgae) to do what your trying to do. Deffinately a good idea.

#4 gerald

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Posted 20 January 2011 - 01:03 PM

I would grow Cryptocoryne, swordplants, Anubias, and/or others that I could trade in for supplies at my local fish store!

Could your HOB plant trays also be a CO2 source for the submersed plants inside the tank, if you use soil and slow flow rate?
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#5 mywan

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Posted 20 January 2011 - 03:22 PM

Thanks exasperatus2002, I was coming at it from the direction of wastewater treatment technologies and searching the "bog filter" term supplied me with a new set of data to work with. It's primarily concerned with pond or water garden filtration, but that's primarily just a matter of scale. A quick review shows a suggestion that the bog should be 10% to 20% of the pond area. I am greatly exceeding this in the worst case scenario with a 12" HOB bog filter. However, an aquarium tends to operate with a higher bioload than ponds do, so it's probably well warranted.

Gerald, I'll have to think about the CO2 "source" issue more. I know that the total surface area of the water is greatly increased, decreasing the need for aeration. I also know that the plants are only dependent on atmospheric and soil CO2, leaving the water dissolved CO2 available for aquarium plants. I also know many bog plants produce oxygen at their root, to promote a symbiotic relation with nitrifying bacteria. Hence further reducing the need for aeration. This same process is probably photodependent even in the root (?). Presently I was researching the water softening and PH reducing effects, but I will definitely look into that question more deeply. Thanks for the "trade" suggestion, that should come in handy in this hobby.

View PostEricaWieser, on 20 January 2011 - 11:37 AM, said:

I really hope you go through and build this because I think it would be beautiful.  
Here is a picture of a neat paludarium:  http://showcase.aquatic-gardeners.org/2008.cgi?&op=showcase&category=3&vol=-1&id=154  If you ran a trickle of water down the back wall, it would be cleaner by the time it reached the bottom.
That first picture of the planted wall looks a lot like what I had in mind for the back wall of the paludarium I am planing. Nice! I also have a bog planned at the base of my waterfall, underneath which is a sloped lower light region of the aquarium for certain fish to feel hidden and safe.

The HOB bog filters I want to experiment with are designed for standardized aquariums though. I think that would be more useful to a greater number of people, and possibly help overcome many of the issues many new aquarist face. I've already started a few drawings to outline a design made from frp board, but still need choose soil depth, water depth, etc., which I need to research a bit more. I presently have a 5, 10, 20, and 55 gallon aquarium to work with. I think I'll go with a HOB bog filter on all 4 of them.

I'll document it as carefully as possible. I may even try cycling some really bad swamp water through it and see how effectively the water gets cleaned, and how long it takes. Perhaps I should use some cheap plastic tubs for that experiment. Who wouldn't want a filter you could dump sewage in, wait for it to cycle, and add fish?

#6 mywan

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Posted 20 January 2011 - 03:34 PM

View Postgerald, on 20 January 2011 - 01:03 PM, said:

I would grow Cryptocoryne, swordplants, Anubias, and/or others that I could trade in for supplies at my local fish store!

Could your HOB plant trays also be a CO2 source for the submersed plants inside the tank, if you use soil and slow flow rate?
Apparently the answer is yes, as a result of the biological processes of the nitrifying bacteria. These bacteria fulfill their energy needs by oxidizing ammonia and nitrites, using the oxygen the plants provide for them at the roots, producing CO2 in the process. This CO2 is primarily inorganic carbon dioxide fixed in the soil, to the benefit of the plant that supplied their oxygen. So it's still an open question how much of it will get dissolved in the irrigation water. Looks good though.

#7 Erica Lyons

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Posted 20 January 2011 - 05:41 PM

View Postmywan, on 20 January 2011 - 03:34 PM, said:

So it's still an open question how much of it will get dissolved in the irrigation water. Looks good though.
My bet would be 2 ppm or so.  Water in equilibrium with the atmosphere is 2 ppm CO2.  
To get more, you really have to inject CO2 into the water with a tank or a fermentation reactor.

#8 mikez

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Posted 20 January 2011 - 05:43 PM

I've done it a couple of times over the years.
My contribution is of limited value for two reasons; one I don't use test kits so I have nothing for the number obsessed scientific types, second, for the life of me, I can't remember the name of the first plant [a common terrestrial houseplant] and I never knew the name of the second [an emergant semi-aquatic which I collected wild].
The first is a wicked common houseplant, often seen in offices. Spider plant maybe? It sends out shoots that typically are allowed to hang down below a hanging planter. Cuttings are often started in cups of water which gave me the idea. I stuck cuttings in a cheap HOB overflow type Aquaclear imitator. The roots invaded the course thin filter sleeve and rooted firmly, growing the tiny fine roots that fail to grow in a plain cup of water. I'm sure they greatly benifited from the mulm that accumulated first on the sleeve and later on the thick root mat that covered it. The foilage grew like crazy and I trimmed in often and gave cuttings to anyone I could. I like to think somewhere a spider plant is growing in someone's house that started in my tank. A catastrophic longterm power failure during winter killed the inhabitants of the tank and I broke it down.

The second plant ironically I collected from a wastewater plant effluent channel. I worked at the plant at the time and the effluent was very clean [I ran the lab and did the testing]. In fact, the effluent was said to represent 80% of the volume of the headwaters of a medium sized river. Sadly, due to downstream treatment plants not so efficient, our effluent was cleaner than the main stem river a few miles downstream. :sad2:  
Anyway, in my lame unscientific way, I always called the plant water cress but I don't really know what it was. :blush: I originally collected it becuase it was so thickly infested with scuds. I found it did well under my lights and looked really cool when it ermerged through the surface and kept growing. Eventually it spilled out and down the side of the tank and made a very thick green blanket which finally overgrew everything and looked like a big bush.

Not too useful, I admit, but my point is, emerged plants are easy to grow and can't help but remove nutrients. Obviously something somebody less scatterbrained ought to persue and document and share here. :biggrin:
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#9 mywan

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Posted 20 January 2011 - 09:00 PM

Interesting Mike. The Spider plant (Chlorophytum comosum), or Airplane plant, is actually a member of the lily family. They generally have a white strip down the middle of long thin leaves, though some variation occur. When their root get bound they produce spider like baby plants at the ends of their leaves. This is actually a mode of reproduction, and the 'spiders' even have their own root system. You can read about them in more detail here:
http://www.arhomeand...plane_plant.htm

I'm more interested in what the second plant might have been. The best that can probably be done though is if you'll tell me where it was collected. I'll do my own homework from there. I have run across a plant that is somewhat similar to watercress, and I'm having a real hard time identifying it. My best identification was wrecked here on this forum.

I'm finding the native choices rather limited in the literature. Most, like cattails, is too large for my purposes. I'll go with some of Gerald's plant suggestions, but would also like to work with some native plants. I definitely want this filter to carry a scud colony, or some similar food species.

#10 mikez

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Posted 21 January 2011 - 08:28 AM

View Postmywan, on 20 January 2011 - 09:00 PM, said:



I'm more interested in what the second plant might have been. The best that can probably be done though is if you'll tell me where it was collected. I'll do my own homework from there. I have run across a plant that is somewhat similar to watercress, and I'm having a real hard time identifying it. My best identification was wrecked here on this forum.



The plant was collected in the effluent channel of a treatment plant in Ma. I have also found it growing in murky nutrient rich streams and seeps that may be influenced by leaky septic systems. In nature it does not grow upward when it's at the surface, instead the small round leaves float and cover the surface similar to duckweed. It grows in long strands which when I trained them up and out of the tank, continued to produce foilage. The stems put out roots but they are fine and not robust.
The stuff can grow very thick even in moderate current. At the treatment plant they used to send a laborer in waders into the channel to thin it out. Light green in color. I called it water cress because the channel reminded me of photos of weed chocked chalk streams in England. I believe they called that plant cress.
I had some cool pics of that tank, some of my first ever digital photos. Unfortunately I uploaded them to one of the first ever free photo sharing web sites and lost them when it failed [no backups].

PS I just googled watercress and although it is clearly not the same, the resemblence in how and where it grows is very strong. The leaves are simpler, thinner and round.

Edited by mikez, 21 January 2011 - 08:31 AM.

Mike Zaborowski
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#11 gerald

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Posted 21 January 2011 - 12:39 PM

Could the plant in Mike's wastewater discharge channel have been a Cardamine or Hydrocotyle species?

Ludwigia palustris would be a good native candidate for the HOB trays.  Grows like nuts and re-sprouts vigorously after major pruning.  Native over much of the US, and fish shops might want your clippings, especially if you have enough light to get good red color.

Edited by gerald, 21 January 2011 - 12:46 PM.

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#12 mywan

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Posted 21 January 2011 - 02:18 PM

I did a lot of searching and I'm not sure what to make of the description. The first issue is leaf size. Looking at watercress pictures the scale is not so obvious, and too many families exist within the constraints. Basically what I get from the description (directly visible parts) is a single round leaf on top of a stem. The remainder of the description is helpful once it starts getting narrowed down to something specific. How big are these leaves (say in relation to a fingers width), and how smooth are their edges?

Perhaps, as Gerald suggested. Hydrocotyle umbellata.

Yes, I will add Ludwigia palustris to my list. I decided, instead of FRP board, to build a bunch of simple wooden trays using cheap 5" wide lumber you can get for privacy fencing. Then line it with cheap poly with the substrate to hold it in place. The poly would probably only last a season, but I can build many of them for next to nothing and swap out for different sets of plants. I need a large water trough to hold the ones not being used on an aquarium.

#13 nativeplanter

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Posted 21 January 2011 - 02:30 PM

Mike,
Trapa natans might be what you are describing if the leaves have toothy edges.  The surface leaves form a floating, spread out rosette that can get, oh, 6-8 wide or so in a good spot.  I've seen it in Massachusetts in a number of places.  Exotic.  Pretty, though.

#14 schambers

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Posted 21 January 2011 - 03:12 PM

I'm eager to hear your results!  I have a couple of set ups at home that might be of interest.  

One is my 100 gallon native stream tank.  I have a large quantity of hygrophilia growing emersed from it, there are a lot of roots in the water with almost all of the leaves out of the water.  It is covered with purple flowers in winter, which is a very welcome sight right now!  It needs pruning, but I hate to do it in winter and lose the blossoms.

The other tank is a 65 gallon.  It has a good quantity of pothos roots growing in it.   I have a grass pickerel in the tank, so I covered it with black egg crate weighed down with rocks.  I took some cuttings from the pothos and stuck the ends through the egg crate.  They are growing quite well and cover the back half of the top of the tank, providing shade to make the pickerel feel more secure.  I got the idea to use pothos from our local zoo's aquarium when I noticed they had a lot of it growing over and around their display tanks.

Both tanks have fluorescent lights above the plants.  Unfortunately, I don't have any test kits.  I almost never test my water, when I feel the need, I take the water to my LFS.
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#15 mywan

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Posted 21 January 2011 - 04:02 PM

Cool!!!

Source (PDF Link):
K. R. Reddy and J. C. Tucker. 1985. "Growth and Nutrient Uptake of Pennywort (Hydrocotyle umbellata L.) as Influenced by the Nitrogen Concentration of the Water", J. Aquat. Plant Mange, 23: 35-40

Quote

ABSTRACT
The effect of varying levels of nitrogen (N) additions on the growth and nutrient removal of pennywort (Hydrocotyle umbellata L.) was evaluated using microcosm aquaculture systems. Biomass yields of pennywort increased from 11.7 to 15.7 g (dw) when-2 day-1 when plant available N in the growth media was increased from 303 to 1513 mg N m-2 day-1 (4 to 20 mg N l-1). Further increase to 40 mg l-1 did not increase the yields. Nitrogen release from underlying sediments supported a biomass yield of 5.4 g (dw) m-2 day-1. Nitrogen concentration of the plant tissue was also increased with each increment level of N in the culture medium up to 20 mg N l-1 (1513 mg N m-2 day-1). This represents a maximum N uptake rate of 41 mg N g-1 (dw) of plant tissue. Nitrogen uptake by the plants cultured in the systems with underlying sediments was 20 mg N g-1 (dw) of plant tissue. Phosphorus uptake was in the range of 9.2 to 10.2 mg P g-1 (dw) of plant tissue at all levels of N additions. Underlying sediments supported a P uptake rate of 4.3 mg P g-1 (dw) of plant tissue. The potential N and P removal rates by the pennywort system during winter months were found to be 321 to 645 mg N m-2 day-1 and 103 to 106 mg P M-2 day-1, respectively. Results of this study indicate that pennywort can be successfully grown during cooler months and can be used as a substitute for water hyacinth in a water hyacinth-based wastewater treatment system.
(Red ink added)
Looks like chasing after Mike's mystery plant actually lead somewhere  :D/ .

Now I need to see what information I can find on the capacity for phytoremediation of heavy metals with pennywort.

Edited by mywan, 21 January 2011 - 04:12 PM.


#16 mywan

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Posted 21 January 2011 - 04:36 PM

Cool again!

Source URL:
Majeti Narasimha Vara Prasad and Helena Maria de Oliveira Freitas. "Metal hyperaccumulation in plants - Biodiversity prospecting for phytoremediation technology", Electronic Journal of Biotechnology, Vol.6 No.3, December 15, 2003

Quote

Several aquatic species have the ability to remove heavy metals from water, viz., water hyacinth (Eichhornia crassipes (Mart.) Solms); pennywort (Hydrocotyle umbellata L.) and duckweed (Lemna minor L.).


#17 nativeplanter

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Posted 21 January 2011 - 04:37 PM

Hydrocotyle stems really don't grow upright like it sounds like Mike's plant can.  They creep along the ground.  If it are growing as a floating mat, they creep along the water and the leaves stick up out of the water like little umbrellas.  The leaves don't float on the surface.  It's a really cool genus, though, and H. umbellata is of my favorites - I've even grown it as a house plant in a soggy pot!.

#18 mywan

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Posted 21 January 2011 - 05:29 PM

View Postnativeplanter, on 21 January 2011 - 04:37 PM, said:

Hydrocotyle stems really don't grow upright like it sounds like Mike's plant can.  They creep along the ground.  If it are growing as a floating mat, they creep along the water and the leaves stick up out of the water like little umbrellas.  The leaves don't float on the surface.  It's a really cool genus, though, and H. umbellata is of my favorites - I've even grown it as a house plant in a soggy pot!.
I didn't figure it was likely to be Mike's plant, but the search still provided some very useful resources. I will definitely be working with some pennywort. I'm going through the metal hyperaccumulation paper now for more potential species. Especially interested in rhizofiltration in plants.

#19 nativeplanter

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Posted 21 January 2011 - 05:41 PM

Out of curiosity, why are you so interested in metals sequestration?  I would think that under normal circumstances it shouldn't matter too much.  (Perhaps if you were trying to remove copper-based medications.)

I hope you do build this - I'd love to see how it comes out.

#20 mikez

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Posted 21 January 2011 - 06:28 PM

wow, this is getting frustrating. I've spent a bunch of time on google, searching every which way including all your suggestions.
No luck!

The various pennyworts seem close but so far none match.

More details;
The stems DO NOT grow up and out. They stretch out across the surface. I got mine to grow emersed by taking the long stringy stems and draping them over the side of the tank where they hung down limp but continued to grow.
And stringy is what the stems are. Very thin and fragile. Although the roots are whimpy and prefer soft mushy substrate, if you grab a clump and pluck it, you're likely to break off the stems rather than pull up roots.
The leaves are small, pinky nail to thumbnail size. I don't recall any teeth but I'm not positive. As best as I remember, the leaves lay flat like duckweed. No umbrellas.
This is not a pond plant. I've found it in streams, which the effluent channel essentially was, or seeps. I have collected it in several locations primarily for the inverts that infest it. Sometimes though it grows in stinky muck and the inverts tend toward rattail maggots.

almost any other time I'd just go grab some and post pics. Unfortunately, we have an obnoxious amount of snow covering everything and sub-zero temps coming next. If we don't figure it out soon, I'll have to just find some.
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