[Asgard]

there are several species of hornworth
you might have the Ceratophyllum demersum (Rigid Hornwort)

 

[Asgard]

Definitely not one of my favourites. I've had very little luck growing this plant, but I've been told like hygro it is ideal for controlling phosphates in excess of 1 mg/l. Same goes for nitrates. I have Horwort C. demersum which forms rigid stems.

Ceratophyllum and Eleododensa species are fast growing and use a lot of nitrate (competing out green algae), provide Oxygen, and secrete an anti-bacterial substance as well as using a lot of phosphate so also reducing the change of blue algea which is a bacteria. They also help micro-organisms to flourish (helpfull in shrimp tanks). I find the biggest drawback that I have to prune a lot, because they are so fast growing, especially in my small tanks (20G). I find them very easy to grow and have them also outdoors in ponds, they even survive frosty winters.

 

[Asgard]

Ceratophyllum demersum (hornwort) and egeria densa (elodea) are two of my favorites. I would like to learn more about them. Do you have any references on the anti-bacterial substance they secrete?

I have no refereces on the substance itself, but the process is called Allelopathy.
A few other plant species can do it as well, Stratiotes sp., Chara sp. , Myriophyllum sp.
Some reading for hornworth, as for the substance try google for Allelopathy or Allelopathic effect. It's a plant defense against bluegreen algae (cyanobacteria) and green algea.