Hornwort as a Water Softener?
Hello WWM Crew, An uncharacteristically brief questions from me, this time. I have
read in a few places that hornwort will soften water. Is this true? If
so, should I remove it from my cichlid tanks? Thanks, Ben
< This is really an amazing plant that doesn't get enough credit. I saw hornwort all over the bays and inlets in Zambia while diving in Lake Tanganyika a few years ago. It looked like little wire brushes. When I returned I read up on this plant and found out that it actually gets its carbon dioxide from breaking down the bicarbonate in the water. Pretty amazing. During the process CO2 is removed and you get a calcium carbonate that actually increases the pH. Since coming back I have added hornwort to all my African tanks because they can handle the hard water and do a great job absorbing nitrates from the water.-Chuck>

Growing (or not) hornwort
I must be the only person that can’t grow hornwort!!
I read the bit on people trying to eradicate it and had a laugh. Does it
need high levels of nitrate?? Since my vals, hygros, java ferns and
anubias have become established in my tanks, the hornwort is struggling.
It gets lots of light and I fertilize weekly with Hagen Plant pro as
well as use Jobes spikes under the gravel for the vals and hygro. When
the tanks were cycling the hornwort grew so fast I had to toss out scads
of it. Alas no more.
Is it a lack of nitrates??
< Could be a couple of things. Hornwort is found all over the world and adapts to different conditions. I found some in Lake Tanganyika in Africa. First question is how old are your light bulbs. Lights loose intensity over time. Any bulbs over 6-12 months old should be replaced. Second is the other plants are now competing with your hornwort for nutrients and they are probably better adapted to absorb nitrates then the hornwort. Based on what you have stated it sounds like the hornwort likes ammonia created during the cycling stage better than the nitrates in the established tank. Sometimes the variety of hornwort we commonly get in the aquarium trade does not do well in warm water tanks.-Chuck>
Thanks
Julie Riley

Hornwort and salt
Hi from New Zealand
<Hello from sunny Southern California>
We (the Department of Conservation) are contemplating using salt to eliminate Ceratophyllum demersum (hornwort).
<Mmm, this is Bob (Robert) Fenner... a long time pest control applicator and advisor licensee... someone had to qualify for our company's service division... and past member of Aquatic Plant Management Society, et al. organizations... involved in Hydrilla eradication programs here... and an all-round pet-fish sort of guy... who has cultured, sold large amounts of this plant (aka Coontail to folks here in the States). Not easily controlled with salt... we can/should talk over other control mechanisms... including commercial herbicides.>
Hornwort is presently New Zealand's most invasive exotic macrophyte. Although hornwort has been present in the North Island since the 1960s, it has only recently made it to the South Island.
<This stuff "really gets around"... like many other pest macrophytes via fishing gear, waterfowl... even ornamental aquatics mis-use (release to the wild)>
Hornwort is a multi-million dollar pest for North Island hydro-electric power generators, principally because it causes blockages in dam turbines (the scope for disruptions to South Island HEP schemes is potentially even greater).  Hornwort is also capable of displacing the majority of our native macrophyte species and even some of our most invasive introduced macrophytes including Egeria, Elodea, Lagarosiphon.  
<Does so in the U.S. as well>
Fortunately eradication a still a realistic option (in the South Island) because of the limited extent of the present infestation.  A number of control options are being evaluated, the most promising of which is soil sterilization using salt (i.e. sterilizing the streambed substrate).  We have been able to desiccate the majority of the plant the floating-above ground component) using the contact herbicide reglone (a form of diquat).
<Really... this is the product category (teratogens) I was going to describe... can you related the treatment protocol? Are you using a spreader-sticker? Need to know water temperatures, if you're spraying emergent material...>
However, there is still the possibility of buried propagules withstanding a herbicide treatment hence, we need a soil sterilent that is inert (when in contact with organic matter) and which has a residual action such that it would saturate the streambed and eliminate any remaining viable buried fragments.
<Mmm, yes... but a systemic might likely prove more effective...>
Salt appears ideal in this respect particularly as trials have shown free-floating hornwort will perish if immersed in water of sufficiently high salinities.
<Yes... but for how long, how high a standing salinity... what about the residual salt?>
I was alarmed to learn that hornwort is included amongst a list of macrophytes that are suitable for brackish aquaria.
<Yes, exactly... it is>
Do you consider that it is realistic to expect that, if applied at sufficiently high salinities, salt will also successfully eliminate buried propagules (given hornwort's tolerance of brackish water)?
If so at what concentrations (parts per thousand) should salt be applied?
<Obviously, the only treatment regime I would trust is one that was tested out by assay... I would do a few experiments here... Unfortunately I know Ceratophyllum can be almost instantly placed from fresh to water of a spg. of 1.005... likely higher salt concentrations, w/o suffering apparently.>
I really appreciate your help.
Kind regards
Matt Bloxham
Biosecurity Contractor
Department of Conservation
Motueka Area Office
New Zealand 00 64 3 528 1810
<Do try a few test plots... Again, I would utilize the Diquat (but can suggest other products...) with an oil... on emersed portions at standard dosage... during mid-day to afternoons, at temperatures of 55 F. or higher... Much to discuss re the allowance of other economic poisons in NZ, and concerns re run-off, toxicity issues... Am interested (parenthetically) if you've considered triploid carp species as bio-controls?
Bob Fenner>

Hornwort eradication options
Hi Bob,
Thanks for such a prompt reply, couldn't believe it when I got back from lunch to find your message.
<We aim to please... and must need reply ASAP or get hopelessly buried>
We used a spray contractor to apply the reglone.  He used an Aquagel formulation which was administered in 600mm wide strips (with 1m spacings) across the stream.
<At about 1 gallon per...? Surface area.>
At the time hornwort was at maximum biomass. Smaller infestations amongst willows were spot sprayed. Temperatures were in excess of 15 degrees Celsius (i.e above the recommended minimum operating temp forreglone) and spraying commenced in the morning to avoid problems with
thermoclines.
<Mmm, I am not so much inclined to be influenced by the last... more important that the weed be active metabolically... late morning to mid afternoon on sunny days>
The worst affected stream section has significantly reduced flow with large areas of standing water (i.e. plenty of herbicide contact time) and was not at all turbid. It has been nine months since the Aquagel was administered and there is still no sign of hornwort regrowth.
<Good>
We are just coming into summer and in New Zealand, hornwort typically reaches maximum biomass in Autumn.
<Yes, same here... late summer into mid-autumn>
The contractor believes that the reglone will eliminate the hornwort completely but we have reservations because of the issue of buried fragments which the reglone is unlikely to touch.  Unfortunately there are no systemic aquatic herbicides presently registered for use in New Zealand.
<Ahhh... a shame. Shortsighted... more pollution, trouble from their lack of availability, use.>
We have certainly thought about using triploid grass carp, but decided against for the following reasons:
This control option would involve significant habitat manipulation. For example, shallow areas of Moutere Stream would need to be deepened.
<Really? Have seen the big three species used in very shallow waters... even have some footage of a Ctenopharyngodon "going terrestrial"! to get at shoreline growth.>
If this control method were to prove unsuccessful, deepening stream sections may increase the suitability of these areas for further hornwort infestation (by slowing flow and increasing the rate of mud deposition).
<Possibly>
* Use of grass carp would rule out the option of simultaneously treating Moutere Stream's hornwort and pest fish populations (using the same methods).  Grass carp could only be introduced into Moutere Stream after attempts to eradicate pest fish had been concluded.  Any pest fish eradication attempt would ideally involve significantly dropping the water level (in addition to applying a piscicide) which would benefit other hornwort eradication options but not the grass carp control option.
* We understand that Grass carp are inefficient digesters of food; half of the weed eaten may pass through the gut undigested.  Hence, there are doubts over whether grass carp are able to digest/process hornwort sufficiently to neutralize any viable propagules. The widespread dissemination downstream of partially digested vegetative matter/propagules is undesirable in a running water system such as Moutere Stream.
<Would only establish a predator-prey equilibrium/dynamic>
* The introduction of yet another exotic fish species to this stream: runs counter to the Department's objective of minimizing impacts from introduced freshwater fish species in the Nelson region as the stream already contains a significant biomass of tench and Gambusia.
We intended dewatering the affected stream section using a weir and pumping to land so that the salt could be applied directly to exposed streambed, as we figured this would help maintain salt in its most concentrated form. We will certainly look at testing the salt by assay.
<Only way to assess practicality, effectiveness.>
Meanwhile, if you can think of any other way of eliminating the hornwort outright (including the buried component), we would certainly love to hear back from you (it is unfortunate that systemic herbicides are not an option for us).
<Well... is the area involved absolutely huge? Have you done any testing re how deep the propagules are/might be? Another possibility (has been used for Hydrilla verticillata infestations in areas in excess of 50 hectares...) is to de-water, Vapam with cover (optional), scrape and remove sediment... to waste, fill areas... even to the sea... Expensive, drastic... but another possibility. Bob Fenner>
Thanks again for your help Bob.
Kind regards, Matt Bloxham

Looking for Hornwort/Coontail/Ceratophyllum demersum...
I would like to know if you can buy the Coontail/hornwort at a store. If not, is there any way to grow this plant? please send a reply.
<Ceratophyllums grow very well in most any type of hard, alkaline water with sufficient light. This is a popular genus of aquatic plant in many places around the world. Bob Fenner>