A DOLLOP ABOUT DUCKWEED

Really smart people may not have this problem, but a planted aquarium, it seems, always winds up with a duckweed infestation...

Original post moved to the blog on http://www.myaquariumclub.com/duckweed-control-50.html

That is pretty interesting! From what I have read about hornwort it makes perfect sense. I read they will use up ALL the nutrients in the tank. I guess the normally overbearing duckweed has to work extra hard to take what it can get while the hornwort is around.

The hornwort must have had something to do with the chemistry of the two aquariums I set up last month. They still don't have measurable amounts of ammonia.

John - you rule

This is my guess for the explanation - I think that there is a race among all flora on aquarium over minerals, CO2 and light.

Unlike many rooted plants, duckweed floats and thus have a major light advantage over them.
The disadvantage of floating is that you only get minerals from the water, unlike rooted plants which gather minerals from the gravel too.

If the aquarium is heavily planted, there are hardly enough minerals left on the water, and non rooted flora starve.

Hornwort specifically is probably extremely effective since it grows fast, consuming large amounts of minerals to support it's growth and it can grow long enough to float, so it can get large amounts of light.

What do you think?

That's a good point. I know that plants absorb minerals from the soil, but i read somewhere that land based plants use those minerals to help them absorb nourishment from the air. Similar things probably happen in aquariums, all of which helps explain how live plants keep the planet clean.