Duckweed index

Big Fish article, Experiment, highlight
Lemna sp. in 12 wells with different conditions.


The duckweed index has been invented and popularized by  the user dw1305 at . He actually used Limnobium sp. which in the hobby is more commonly known as “amazon frogbit”. He describes the process as:

“… when the Limnobium looks like the plant in the bottom left hand corner of the image I feed with KNO3 (to give 2ppm K). If this doesn’t produce a rapid greening, I then add macro / micro elements. Subsequently I change the water to achieve my preferred conductivity and then only feed again when the “duckweed” index indicates I need to. ” You can read mor at the ukaps forum page. The index seems simple to use, when visible yellowing is observed first address the most likely limiting nutrient for floating plants : nitrogen. If this does not work add some other macro  nutrients and end up with micros.  He rightly argues that this system should mainly be used in low light systems, because the latency is pretty large and more sensitive plants will suffer more. While the idea is interesting, I was unable to find very good examples of different deficiencies or tests to see if the duckweed index works.

However, his idea made me curious. How would common duckweed (Lemna sp.) behave under different nutrient conditions. Lemna sp. is an excellent model organism for aquarists. It is an aquatic plant that takes all the nutrients from the water column and has access to atmospheric CO2. Therefore, there is little chance of CO2 limitation  and no need for substrates. It also has a relative small size and a very fast growth rate.  Perfect.


On this page I would like to provide better documentation and examples of how deficiencies in Lemna sp. look  and behave. This is done in attempt to test if we can actually have a better informed and improved “duckweed index”.


More about the methods will be presented soon as the experiment is ongoing.

5 thoughts on “Duckweed index

  1. Hi,
    Darrel here, I’m the UKAPS member mentioned in the original post.

    I’m interested in any results from this. I’m not in a position at the moment to carry out this growth trial, but it is something that I should have done when I had the chance.

    I didn’t really invent the “duckweed index”, Diana Walstad in “the Ecology of the Planted Aquarium” and Horst & Kipper (in “The Optimum Aquarium”) had really got there a long time before.

    Assuming you are going to use Lemna minor? I would adjust the pH of the DI water with NaHCO3, it won’t supply any nutrients, but it should ensure all the treatments stay alkaline.

    You can buy Sachs solutions that are nutrient deficient, or you can make your own (details here: ).

  2. I do believe all the concepts you have offered in your post. They are really convincing and will certainly work. Nonetheless, the posts are very quick for newbies. May you please lengthen them a bit from subsequent time? Thank you for the post.

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