Re: indicator plants and nitrates

MMMORRIS at smith_smith.edu
>	I read your comments about indicator plants like duckweed, and adding 
>nitrates in the aquatic plant newsgroup last week.  You mentioned something 
>that intrigued me and I was wondering if you'd have the time to elaborate or
>point me in the right direction article/book wise.  What do you mean that you
>prefer to use indicator plants such as duckweed as opposed to test kits?  

Basically, I am lazy and cheap. I do not have the patience to run
colormetric tests and I enjoy using my 'green thumb' to guide my aquatic

>Do you mean that duckweek will prohibit excess nitrates and thus if it begins 
>to flourish you know its to high, so stop feeding, change water, etc, or do 

>you mean adding duckweed and the added eventual detrius will add nitrate to 
>a fully planted nitrate starved system?  I'm most interested in the idea 
>of indicator plants in aquaria/water quality.

I also have limited spare time at the moment, so my answer will be somewhat
Some of my heavily planted tanks have very few fish and also get little
food, so the availability of nitrogen (in terms of ammonia and/or
nitrates)is usually in short supply. The same may be true for phosphates,
but between N and P, the N is usually the one that is limiting.  When my
duck weed stop growing and turn pale, this is my indication that some
nutrient is limiting. It could be anything, but with the lightly loaded tank
together with regular water changes, occasional trace element additions and
use of soil) this tells me that N is limited.
From experience with duckweed, addition of small amounts of NaNO3 will perk
things up. When the duckweed starts to reproduce too strongly, it means that
I have nutrients in excess. Because I am lazy, I add N and other nutrients
sparingly because I want to control growth - so I do not have to spend my
weekends trimming (and weeding )all my tanks.   For this reason, my favorite
tanks are some of my low tech tanks.  
Indicator plants are discussed in some of the contemporary aquarium books.
As I recall, they usually mention certain plants as indicators for low iron.
Maybe someone else can find the references and elaborate further.

Duckweed can become a nuisance when nutrients are in excess. Then they must
be regularly harvested. This is a good strategy to reduce algae, but was not
what I had in mind.

Neil Frank, TAG editor          Aquatic Gardeners Association
Raleigh, NC