What is the “Duckweed Index” all about?

[Jorge O'Reilly]

Dunno if it's been mentioned, but here's a side-by-side comparison between duckweed, Frogbit, RRFs and some Spirodela polyrhiza. Sort of an intermediate between the two, if you don't want to deal with the MASSIVE root systems I have on my Frogbits.

 

[dw1305]

Hi all,

some Spirodela polyrhiza

It <"does get a mention">, I've tried it a couple of times, but it needs harder, more nutrient rich water than I have to offer. If you can provide that? It should work fine.

cheers Darrel

 

[PARAGUAY]

Salvinia does really well in my aquariums and l can sort of work out how much TNC Complete to dose after a while. Now far less than l initially used, just add at water change , all plants seem to be doing well

 

[hypnogogia]

MASSIVE root systems I have on my Frogbits.

Doesn't the root system get larger when there is a lack of nutrients for them?

 

[dw1305]

Hi all,

Doesn't the root system get larger when there is a lack of nutrients for them?

We think it probably does (via <"resource partition">). My plants tend to have relatively small leaf rosette, but long and bountiful roots, which I think is a response to fairly lean rations.

It is really the ratio of rosette to root that is important, <"if you have a very large plant it will have large roots">. These are @castle 's plants where the roots had reached the substrate <"Looks like my Limnobium laevigatum has flowered?">

cheers Darrel

 

[simon_the_plant_nerd]

Here’s two bits of RRF, both grown under the same light in the same tap water (soft) but the red one has been limited of nutrients. It has taken a long time for the plant to get that deep red colour and you’d probably see nutrient deficiency problems elsewhere before it became a useful indicator.

It is pretty though.

 

[Jorge O'Reilly]

Hi all,

We think it probably does (via <"resource partition">). My plants tend to have relatively small leaf rosette, but long and bountiful roots, which I think is a response to fairly lean rations.

It is really the ratio of rosette to root that is important, <"if you have a very large plant it will have large roots">. These are @castle 's plants wher ethe roots had reached the substrate <"Looks like my Limnobium laevigatum has flowered?">

cheers Darrel

Castle's are absolute monsters. Mine are marginally fuller than yours, Darrel. When the roots reach the substrate it is a PITA too, when you pull them out they muck everything up...

I really like the polyrhizas. They get flak since they look likee lemnas, but they're larger and don't act as a bloody bioweapon so.

 

[dw1305]

Hi all,

I really like the polyrhizas.

That is one advantage of the <"Duckweed Index">, you just need a floating plant that grows happily in your tank <"Giant duckweed - Spirodella polyrhyza"> & <"Id on floating plant">.

The actual plant isn't that important, just that it has floating leaves and grows happily under your usual tank conditions.

cheers Darrel

 

[dw1305]

Hi all,

Here’s two bits of RRF, both grown under the same light in the same tap water (soft) but the red one has been limited of nutrients.

Fantastic. <"I really need"> to have another go with RRF (<"Phyllanthus fluitans">). I got <"fed up of rescuing it">, but they may just suggest that it wasn't very happy with <"the growing conditions">.

cheers Darrel

 

[tam]

I think you'd have to be careful with the RRF as light plays into the colour. I've had it growing packed densly (so much it didn't move) in a tank with the light about 1" above the surface and there was a very noticable line across the plant growth showing the extent of the light - red under the light and green around the edges. I've also taken them out of the tank, and floated them in tank water on the window sill and you get the deep red colouration. It a very cool plant but I think the light reaction adds an extra variable that wouldn't be helpful for the dcukweed index.

When it's happy it will grow over the top of itself and almost convert to emersed type branches where only the base sets of leaves touch the water and root with the offshoots growing up so it's packed an inch or more thick and out of the water supported by other plants below. On the other hand, if it's not happy it disintergrates readily.

 

[Ady34]

I think you'd have to be careful with the RRF as light plays into the colour. I've had it growing packed densly (so much it didn't move) in a tank with the light about 1" above the surface and there was a very noticable line across the plant growth showing the extent of the light - red under the light and green around the edges. I've also taken them out of the tank, and floated them in tank water on the window sill and you get the deep red colouration. It a very cool plant but I think the light reaction adds an extra variable that wouldn't be helpful for the dcukweed index.

When it's happy it will grow over the top of itself and almost convert to emersed type branches where only the base sets of leaves touch the water and root with the offshoots growing up so it's packed an inch or more thick and out of the water supported by other plants below. On the other hand, if it's not happy it disintergrates readily.

This is interesting, I don’t know how significantly this will be a factor, however perhaps those plants under the light are not red directly due to the intense spectrum, but perhaps due to the lighting intensity driving the rate of growth? A very close to the surface light offers little surface spread, those under the light maybe simply trying to grow faster which turns their fertilisation from plenty (like those of the green outer shaded plants) to limited (red under direct strong light) simply due to the dictated rate of growth …the windowsill plants again maybe don’t get the same level of constant fertilisation as the tank so eventually turn red…..just a thought 🤷🏼‍♂️

 

[simon_the_plant_nerd]

I think you'd have to be careful with the RRF as light plays into the colour.

I don’t know how significantly this will be a factor

Here’s some RRF I left in a bucket. The lighting is poor. The nutrients even more so. You can see the older growth still has a little green tint to it but the newer growth is more red. It’s the same across the bucket. It looks almost brown in this photo because the lighting is so terrible. 😄

 

[PeerUnk]

Hi all, reading along in this forum quite some time. This is an interesting thread. Duckweed is not my thing. Tried Limnobium more than 20 years ago, but never survived. Back than I believed NO3 and PO4 was root of all algae bloom I had in my tank. Until in 2008 the approach of Estimative Index came into my life. That was a major shift in thinking about nutrients, and my plants loved that. Nowadays I use Salvinia to check whether Fe and trace are needed in a small more neglected tank. Does new leaves gets yellow (and overall growth is poorer)? If so, then dose FE-traces-mix more often.

But checking how green the leaves are as indicator never arose as an idea, maybe ample macro dosing in tap water never gave issues nutrients wise.

But still, Limnobium still is one of the plants I like to try sometimes, and seems a good indicator somethings off. I just got the amazon frogbit in, as well as Phyllanthus fluitans to give that a go as well.

Okay, so let me try to recap.
Lymnobium as a floater gets it's carbon from the air, and can be used as good indicator plant for the water column nutrients.
If it doesn't maintain a ' darker' greenish look (like some healthy photo's in this thread), nutrient dosing like N, K, P and/or Mg dosing may do the trick.
When new growth is pale and yellowish, a non mobile nutrient dosing can help. Such as S, Ca, Fe, Mn and other traces like Ni, Cu, Zn and B.
For fixing things, it's up to the aquarist to determine whether going for full scale dosing (for instance Estimative Index dry dosing of using an all in one fertilizer), or start checking them individually. It takes time for a plant to recover, so maintaining higher nutrient levels seems logical.

@dw1305 Darrel, Am I way off in this recap?

 

[dw1305]

Hi all,

Lymnobium as a floater gets it's carbon from the air, and can be used as good indicator plant for the water column nutrients.

Yes, that is it, a floating plant has access to <"atmospheric gases"> and will never be carbon limited. It is also nearest the light, so again lack of light shouldn't ever be an issue. The third thing is that they are <"plants adapted to very bright light">, so leaf scorch shouldn't be an issue either.

If it doesn't maintain a ' darker' greenish look (like some healthy photo's in this thread), nutrient dosing like N, K, P and/or Mg dosing may do the trick.

My original Duckweed was Lemna minor, but it has the disadvantage of not enjoying soft water or growing at very low nutrient levels. The advantage of Limnobium (Hydrocharis) laevigatum is that it will grow across the whole range of nutrient and hardness levels.

When new growth is pale and yellowish, a non mobile nutrient dosing can help. Such as S, Ca, Fe, Mn and other traces like Ni, Cu, Zn and B.

Yes, that is exactly it. The most likely non-mobile <"micronutrient deficiency"> is iron (Fe), but any of the 14 essential mineral nutrients can be deficient.

For fixing things, it's up to the aquarist to determine whether going for full scale dosing (for instance Estimative Index dry dosing of using an all in one fertilizer), or start checking them individually.

I usually recommend an "All in One" for the mobile nutrients, purely because there are a lot of them, and deficiencies of many of them show similar symptoms. In terms of nutrient addition you can regulate plant growth by varying their amount, but not all plants will grow under a <"lean dosing regime">.

It takes time for a plant to recover, so maintaining higher nutrient levels seems logical.

If it is a mobile nutrient that is deficient then the plant should green up pretty quickly once it becomes plant available. I'm not after optimal plant growth, I actually want slow and sustainable growth. The advantage of Amazon Frogbit is that it can <"respond rapidly"> to any <"sudden increase in nutrient levels">, although that response is actually quicker in Lemna minor.

cheers Darrel

 

[Connswater]

All good stuff. Duckweed has always been a pain for me, except as a child in the 1960s, it was then the only plant that grew in my little plastic tank with one feeble small fluorescent tube. Did a great job for water quality and saving fry, but had to be scooped out twice a week, and gets everywhere, sometimes even then into my childish sugary tea! I no longer put sugar in my tea or have duckweed. I find Frogbit really useful, responds fast to nutrient deficiencies, and is manageable, Salvinia is present in my tanks, and will brown if Iron or other nutrients are lacking but is still a bit like duckweed and can prove bothersome. For larger tanks, especially if a bit on the deeper side, Indian fern works fantastically, with great dangling roots and interesting aerial growth, looks great even when planted submerged. I find it a bit slower to respond to deficiencies but it is very manageable and does the job over a few weeks of alerting me to any issues, and, is simply the best plant for fry salvation, my black mollies are a self perpetuating community thanks to it.

 

[dw1305]

Hi all,

Did a great job for water quality and saving fry, but had to be scooped out twice a week

In some ways, for people with harder water, Lemna minor or L. minuta, are still the <"best nutrient indicators (and reducers)">.

The Duckweed Index is called the "Duckweed Index" <"because originally it used Lemna minor">.

I stopped ,"using Duckweed">, because:

• People have an (irrational) hatred of it.
• I found that it doesn't do well in soft water,
• or under low nutrient conditions,

But give it hard water and plenty of nutrients? It grows like wild fire.

<"Removing Duckweed (Lemna minuta) - any natural solutions?">.

I find Frogbit really useful, responds fast to nutrient deficiencies, and is manageable

Those are some of the main advantages, it still grows fast enough to be useful - <"Hi everybody,">, but is much more tolerant of lean dosing and soft water etc.

Salvinia is present in my tanks, and will brown if Iron or other nutrients are lacking but is still a bit like duckweed and can prove bothersome.

<"Salvinia auriculata group"> would be equally suitable for the "Duckweed Index" if it had a <"leaf green"> frond, because of the hairs it is more difficult to judge <"greeness">.

For larger tanks, especially if a bit on the deeper side, Indian fern works fantastically, with great dangling roots and interesting aerial growth, looks great even when planted submerged

Indian Fern (Ceratopteris spp.) are other plants that <"a lot of us grow">, I use it as an emergent and <"sub-surface floater">.

simply the best plant for fry salvation, my black mollies are a self perpetuating community thanks to it.

Floating plants are really good for fry survival, I think a lot of use have found <"stray surviving fry in our tanks"> in a way that doesn't happen for people who don't have surface plants.

cheers Darrel