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FAQs on Hornwort/Coontail

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Aquatic Gardens

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by Robert (Bob) Fenner

Ceratophyllum demersum     11/26/14
Happy Holidays Crew, What are thoughts on any negative effects of Hornwort on phytoplankton blooms, if any? I'm having second thoughts on using this plant in my fry tanks. Thanks in advance. Aloha Brandon
<Ceratophyllum, under suitable light, will inhibit the growth of many (but not all) types of algae according to the scientific literature. But as is usually the case with allelopathy, the impact is variable and depends upon the macrophyte (i.e., the plant) being in good health and growing quickly (i.e., receiving lots of light). Ceratophyllum is a common choice for fry tanks, not so much for algae control (it probably doesn't do a huge amount of this under indifferent lighting) but because it provides shelter and the fine leaves trap organic food particles where Protozoans can prosper, and these in turn are excellent food for baby fish. Cheers, Neale.>

Lighting question... nebulous      5/17/14
Hello. I have a 29 gallon glass aquarium. My lighting system is a 30"
Single Fluorescent Aqueon Aquarium Strip-Light
It takes t-5 bulbs.

My question is as follows:
Is a 24", 24 watt, 6,700k
Current T5 High Output TrueLumen 6700k Aquarium Flora Bulb
Too strong for my lighting system?
<Not likely too strong for anything...
Have you read on WWM re whatever you're illuminating here? Do so. BobF>
Re: Lighting question      5/18/14

Thank you.
Light Bulb replacement question      5/20/14

I am planning to add north American hornwort (Coontail) to my aquarium. I hear it can tolerate low light levels.
<In cold water and ponds yes; but in tropical tanks needs better light. Not necessarily strong, but fair, 1 watt per gallon upwards. Think about it this way: the higher the temperature, the faster its metabolism will be; the faster its metabolism, the more food it will need; the more food it needs, the faster photosynthesis will have to run; the faster the rate of photosynthesis needs to be, the stronger the light intensity must be.>
I already have 1 Anubias petite plant in my aquarium, which likes very low light levels.
<Indeed; or more precisely, in bright tanks needs to be a shady spot.>
I have a 29 gallon long tank. It is about 18" high, 3 ft. long. I have a 30" standard fluorescent lighting system. The single bulb currently in my system is a 24" standard fluorescent bulb of about 1" in diameter. Can I replace this bulb with a 24" t-5 high output bulb of 24" ?
<You cannot normally swap T8 and T5 tubes. T5 tubes have specific "caps" that fit on each end on the tube. But many modern hoods can be adapted to fit/use either type of light. Refer to your manufacturer or retailer for specific advice. Cheers, Neale.>
e: Light Bulb replacement question      5/20/14
Thank you Neale.
<Most welcome.>

Re: How often do you feed cherry shrimp? - 12/18/2012
Hope this works.
The one at the top.
<Is Hornwort.>
(That lime green endler female also pictured was so big when I got her...and she'd faded white from stress.  I thought she was another type of fish until her green coloration came back.  The guy assured me the fish hadn't been mixed.  Who would have thought with the male endlers so tiny. 
They're neon size!)
<Real good. Cheers, Neale.>
Re: How often do you feed cherry shrimp? Hornwort...  - 12/18/2012

It's hard to believe that this beautiful plant:
<A short-term planting of Hornwort on the substrate… usually doesn't last long there.>
is really the same plant family as this pond like messy looking plant, though it is:
<Same plant.>
One has good manners and a delicate form, and the other sheds all over the substrate and flops on all of the aquarium furniture.
<Hmm… I think it has something to do with where the Hornwort was collected, and whether it's been kept under intense lighting, hard or soft water, at tropical or coldwater temperatures.>
oh well, the fry need to hide low as well as high.
Thanks Neale!
<Look up the words "ecophenotypic variation". Plants are modular and vary their appearance (and to some degree physiology) depending on where they are and how well they can grow. Cheers, Neale.>
Re: How often do you feed cherry shrimp? - 12/19/2012

<Indeed. Neale.>

Snail success story.....re: Snail mug shots       thanks again!!  Snail control f'     12/11/12
Well Neale....I stumbled upon a snail trick that works, and feel I ought to share this for other folks with similar issues.  This didn't get them all but it thinned them to more manageable proportions.
<Ah, this is often the case, and if you fix the underlying problems with your tank that allowed a snail "plague" to develop, may be all you need to do.>
If you recall I was going to tear down and clean up as snails were even eating the java ferns.  I'd found a substrate I liked at the local small business garden shop to replace my snail infested batch.  Tiny dark river pebble mix, well worth waiting for.  But, it never came in!
Then the local fish store gave me free hornwort as they'd promised the same weekend that the substrate didn't arrive.  But rather than it being the lightweight, attractive floating type that holds together nicely that I'd expected, it was the coarse, scruffy dog, flop to the bottom and crawl on the decorations and shed all over the place type.  I threw it in, as it was meant to be a temporary fix anyway...I needed something, and I couldn't wait on the substrate.
This ended up being a good decision, because the snails were no longer so visible on the glass the day after.  I had to clean and vacuum more frequently, and I would pull the hornwort (aka: snail magnet) out and rinse it and remove tiny snails.
I discovered that coarse hornwort that falls to the bottom apparently is a perfect snail bait, and you can rinse them off resulting in a quickly reduced snail population.  It is worth having to clean the gravel an extra time or two.  And it starts to grow on you, though I'll be glad when I can build up stock in other more elegant plants.  I do have Indian fern now, and my Anubias is slowly sprouting and one of the crypts is somewhat recovering from her meltdown.
I did read that hornwort is a heavy feeder so I'll feed lightly to help the other plants.
<I don't find it does terribly well in tropical tanks without intense lighting, lasting at best 6 months or so, but your own experiences may be different.>
I also saw a cute thing on the virtues of hornwort here:
They suggest swirling a net around to stir up the drop-off and scooping it out.  I vacuumed again anyway,  but using the net after the vacuum when things were stirred up proved the most effective way to remove stray hornwort fur.
Thanks again.  It may not be the best option (don't get snails in the first place and stock new tanks with assassin snails), but it looks like I've been saved some work.  It is the best snail trap I've found yet....it works like beer in a capful in your flowerbed to trap earthbound slugs.  And it's shedding less and seems to be adjusting.
<Thanks for sharing. Cheers, Neale.>
Re Snail control f'     12/11/12
I agree, the hornwort definitely won't last!  It never did with the Betta tanks which have incandescent light near by and super thriving java plants which do like that environment, and I gave up on it a long time ago for Bettas because I hate when it sheds and dirties the water (as Anacharis unfortunately does as well).
<Indeed. The problem with keeping coldwater plants in tropical tanks is that they grow really fast at first, using their stored energy, but eventually need really strong lighting otherwise they "starve" and then start rotting.>
I'm just glad it was free this time and he gave me so much of it too, and it finally gave me a way to remove snails easier than trying to catch them off the glass in paper towel.
Have a nice week.
<So far, so good! Neale.>

Freshwater object ID: Looks like a seedpod\sporophyte. 2/20/2010
<Hi Evan.>
I found this in my freshwater invertebrate planted tank.
It was in a clump of Hornwort. I'm pretty sure this is a Hornwort seedpod.
Any idea how I might grow it?
<It doesn't look like a hornwort sporophyte: See here:
It does look like a seed pod of some sort, but nothing I recognize I'm afraid.>
<Try setting it on the bottom of your tank and see what happens.>

Re: Freshwater object ID   2/20/10
Thank you for your reply. I followed the link you provided, it was for a Bryophyte called hornwort (Bryophytes have neither flowers or seeds). I was referring to Ceratophyllum demersum in my original email. I have not been successful in Googling up a picture of Ceratophyllum demersum seeds/seedpod. I thought perhaps someone at WWM has had hornwort reproduce in their aquarium and could ID my image.
Thanks for your help,
<Is a Ceratophyllum demersum fruit. Forgive my brevity; bit short of time, but wanted to give you a quick answer. Cheers, Neale.>

Abstract Questions from a Freshwater Aquarist   7/31/09
I just have a couple of questions that I couldn't seem to place under the same category (hence the name). Okay, my first question is can ph kill fish?
<Yes. Rapid changes alters blood pH, and this turn affects the ability of the blood to carry oxygen and carbon dioxide around the body. The wrong pH will severely stress, eventually kill, those fish adapted to particular pH levels. A Rift Valley cichlid for example will not do well at pH 6, and will become much more prone to opportunistic infections than otherwise.>
I recently bought 5 goldfish for my aquarium, I set the bags in the water for 15 minutes, then netted the fish and put them in my aquarium. Three hours later (literally) they all died. I checked my water chemistry soon
after, and the only offending thing I could see was a ph below the charts (anywhere from 5-5.4, judging by the color) Nitrate: 40 Nitrite: 0 Ammonia: 45-ish Hardness: Moderate Temperature: about 76 at time of death.
<Goldfish will tolerate pH values across a broad range, at least for a while, but they do best at basic pH levels between 7 and 8. If your pH really was as low as 5, then [a] biological filtration wouldn't be working,
and [b] that low pH could easily have shocked or killed the Goldfish outright.>
My second question: are store-bought fancy guppies of poor (I mean very poor) quality?
<Can be. Essentially the question is the same as this: which are hardier and more long lived, pedigree dogs or mongrels? The answer is of course mongrels, which, on average, consistently outlive their pedigree cousins.
Guppy breeders select in favour of certain traits, such as tails of a certain length, or particular patterns on the body. But they don't select in favour of hardiness or longevity By contrast, evolution selects in favour of "fitness", the ability to survive and breed. There's actually good experimental evidence that supports this. Fancy Guppies cannot be acclimated to living in seawater, whereas wild Guppies and "feeder" Guppies
both can. In other words, when breeders create Fancy Guppies, they seem to throw away some of the genes that made Guppies hardy in the first place. Now, there are differences in quality of Guppies just as there are differences in the quality of pedigree dogs. The Guppies you buy from a pet store were bred to a price, not a quality, and often fish farms use antibiotics to "support" their fish so that they can stock lots of them in breeding ponds without being too worried about healthcare. By contrast, breeders at fish clubs will be taking more care, selecting the best fish, and looking after each group of fish carefully, as a labour of love. None of this gets away from the fact that Fancy Strains are often very inbred, with father-daughter, mother-son crosses being very common, so even under the best of circumstances, Fancy Guppies are genetically "weak". But there is a difference between good quality fish and mass produced fish.>
I've heard that the guppy is supposed to be the easiest and most enjoyable fish in the hobby, and yet I've also had experience (and read on other sites) that suggests otherwise, mostly due to inbreeding and the breeders only selling low-quality fish to pet stores.
<Pretty much. Wild Guppies are astonishingly adaptable, and that's why they became popular in the first place. Fancy Guppies, like fancy varieties of most aquarium fish, are much less adaptable.>
My third question is if I breed natural (feeder) guppies with Fancy guppies, will (some of) the fry be fancy and hardy?
<No; they'll all be "feeder" Guppies, or at least, mongrel Guppies with a mish-mash of colours. To my eyes, such Guppies are lovely, resembling the wild-type fish, which are wonderfully variable. The old name for Guppies, Millionsfish, referred to the fact that there were so many of them, and every one was different.>
My last question is that I've heard (on this site and others) that Hornwort is an amazing and under-appreciated plant. That it eats up Nitrates and Ammonia, looks good, reduces water hardness, sucks up CO2, puts in O2, increases water ph, and is easy to keep. How many (if any) of those things are true?
<Like high-fibre breakfast cereals, while it certain does some good, it isn't a magic bullet that will cure all life's ills! Hornwort, or equivalent floating plants such as Floating/Indian Fern or Amazon Frogbit, are great additions to tanks with livebearers. Your Guppies will nibble at them directly, and also peck away at algae growing on the roots. Yes, they absorb some nitrate (and even ammonia) at a rate depending on light
intensity (i.e., growth rate) and yes, floating plants provide excellent hiding places for newborn fry. I strongly recommend them, but I would expect them to replace your standard protocols for water quality and water
chemistry management.>
I'm looking for a beneficial plant to re-place my withering ones (might help those plants if I turned off/down my air-stones), and then stumbled across the Hornwort.
<Hornwort does need strong lighting at tropical temperatures. It's less demanding in coldwater tanks and ponds. In tropical tanks, sometimes wastes away if the lighting is poor to moderate. Indian Fern and Amazon Frogbit are, in my experience, a bit more forgiving.>
Hope I wasn't any trouble!
<Cheers, Neale.>

Plant Basics - 10/21/2006 Hi, <Hello.> I just bought some hornwort for my 29 gal aquarium. I have about 1 tbsp per 5 gallons for my Mollies and Patties.   <I assume that you mean 1 Tbsp of "salt" per 5 gallons.> How do I take care of the plant? I mean do I need to fertilize or anything else?   <Likely not.  This plant, if left floating, is typically very easy to care for, but can "fall apart" without enough light, especially if you try to get it to root.> Is this considered a brackish water aquarium?   <Mm, probably not, but many plants will not like that much salt.  Hornwort should do okay, though.> I shut off my air pump because I read it will hinder plant growth, is this true?   <Well, yes, in a way.  Aeration can allow more CO2 out of the water than you might desire, since plants consume CO2.  But for just some hornwort, you'll be fine to leave your aerator running.> I was hoping I could get some answers; every where I look I can't seem to get the answers I'm looking for.   <Try "Encyclopedia of Aquarium Plants" by Peter Hiscock.  This is a GREAT book for someone who really wants to get into plants and is just starting out with them.> I like the look of the real plants and the idea of having a aquarium that is as natural as possible.   <Yup, you'll love that book.> Hope you can help!  Thanks,  -B.C. <All the best to you,  -Sabrina>

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>

Aquatic Gardens

Ponds, Streams, Waterfalls & Fountains:
Volume 1. Design & Construction
Volume 2. Maintenance, Stocking, Examples

V. 1 Print and eBook on Amazon
V. 2 Print and eBook on Amazon 

by Robert (Bob) Fenner
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