Gardening at the Top: Floating Aquarium Plants

Author: Steve Waldron

The aquascaping process, for me, is one of adding progressive creative layers. There are layers of inspiration, curiosity, amusement, and intellect that build up long before my hands even get wet.

I might think about a particular aquascape design for years before actually executing it. I like to spend a lot of time researching and daydreaming about my next aquarium project. It’s a nice, therapeutic diversion from daily stresses and worries. Mental creativity keeps me as happy as working with my hands. Once those unseen layers build up and I finally find the time to create a new aquascape, then I start layering the tangibles like soil, stone, wood, plants, fish, invertebrates, water, light, and life.
 
The actual aquascaping process goes very fast for me, and, though it feels like I am in the flow of spontaneity, I have done so much mental preparation that everything comes together rather effortlessly. I feel like the success of my process boils down to how well I have layered the design with forethought, interest, insight, and execution.
 
My aquascapes are on public view in my aquarium shop, and I have to think about how it will impact my customer base by giving my community something to learn from and some fresh excitement. People love novelty, so I have to try out new plants, unusual fish, radical hardscape designs, innovative lighting solutions, etc., to keep folks engaged and coming back for visits.
 
My style is a bit different from what has become the mainstream look for an aquascape, in that I strive to design planted aquariums that function as much as self-sustaining ecosystems as they do aquatic art pieces. I tolerate a bit of mulm in the corner and some black brush algae on the driftwood, and my pipes are never quite as sparkly clean as I’d like them to be. They’re rough around the edges, but my planted aquariums feel wild and free.
 
Despite some aesthetic flaws, my aquariums run quite successfully. The fish and plants are healthy, and my customers always seem impressed. My wild aquascapes don’t need much more attention than a weekly water change, some algae scraping on the glass, and an occasional trim. It all comes down to those layers of forethought that went into the project long before water ever filled the glass box.
 

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Outcompeting Algae

water sprite (1)


Layering biological diversity into the design is an essential element in keeping the look as balanced as possible. I always make sure I have at least one fast-growing plant in every design to outcompete the algae that constantly loom, and I probably use anywhere between six and 20 types of plants in any given aquascape.
 
My tanks are also lush with plant growth, filled with around 60 percent of plant biomass and minimal hardscape. When ] is used, I can count on Rotala, Ludwigia, and other fast-growing stem plants to bust algae before it can even get a toehold.
 
Carbon dioxide (CO2) injection and the accompanied accelerated plant growth are the keys to algae control in most aquascapes. However, I don’t have the financial resources and capacity to add CO2 to all of my several dozen aquariums, so, in those cases, I have to find a different solution for balance and long-term ecosystem sustainability.
 
In these simpler, less technical tanks, I often reach for floating aquarium plants as the great ecosystem stabilizer. Floating plants gather their carbon dioxide from the air and thus are not limited by this essential nutrient and component of photosynthesis.
 
Due to their position at the very top of the water column, floating plants are right under the aquarium light. Even the most basic stock lighting can power quick floating plant growth when the plants are creeping toward the light source.
 
In this way, the floating aquarium plant becomes the engine of fast plant growth that serves to sequester the nitrogen that might otherwise go to fueling algae growth when the other submerged plants in the design are growing sluggishly. In this article, I’ll share a few of my favorite floating plants, some of their prized attributes, and their limitations as well.
 

Water Sprite

tetras under water sprite (1)


Recently I set up a planted aquascape that was not working out quite as well as I had hoped. Light intensity was high, and I needed the appropriate amount of CO2 to fuel rapid plant growth rather than algae.
 
My CO2 regulator was quite old, and I was finding it hard to dial in the proper CO2 concentration with the poorly performing needle valve. In between weekly maintenance, fuzzy algae covered up the hardscape and many of the struggling plants.
 
Despite the constant threat of algae, I decided not to give up on the design, as it had some interesting elements I wanted to see play out to their full effect. I had painstakingly tied Hygrophila pinnatifida to moss-covered manzanita limbs and also tied Riccia to tiny stones sprinkled around the foreground. I wanted to see the Riccia grow, puff out into bright-green pillows and pearl away with oxygen bubbles.
 
Resources were tight, so a new regulator was not in the cards. I needed help in fighting the algae war. In desperation, I reached for that old aquarist’s friend, water sprite (Ceratopteris spp.).
Water sprite or Indian water fern are true aquatic ferns found in many tropical regions that have the capacity to grow rooted in the substrate as well as floating on the surface. I find water sprite succeed best as floating aquarium plants and look amazing with their leafy fronds gracefully arching above the water. Fish love to cavort among the complex structure of water sprite’s many fronds and rambling root structure.
 
Though I had only intended to use water sprite in this particular challenging aquascape as a short-term solution to bring the aquarium into balance, the lacy, bright-green emergent foliage started to grow on me and grabbed the attention of my clients. Soon the water sprite became the dominant design element of the aquascape, and the raccoon tetras (Hyphessobrycon procyon) that populated the tank were seen spawning frequently in the tangled root structure of the ferny mass.
 
Under very intense lighting, the water sprite turned into quite the show specimen, as dense and large as a football. Until I decided to tweak the planting palette of this particular aquarium and replant, that big football was the star of the show at my shop for a few months.
 

Salvinia


One limiting factor for horticultural success with floating plants is water movement. Though I would rate floating plants as among the easiest aquarium plants to grow, their Achilles’ heel seems to be too much water movement. Floating plants seem to enjoy those swampy backwaters where water movement is naturally kept to a minimum and their colonies can create a dense surface mat above the slow water.
 
Too much flow and many of your floaters will erode away into nothing. However, I have discovered that the floating ferns of the genus Salvinia are better at handling a little extra flow than many of the other floating plants out there.
 
One of my favorite Salvinia species is S. cucullata, which grows in thick mats with relatively short, dark roots. The cup-shaped form of the individual leaves is quite beautiful and fascinatingly hydrophobic in the way each individual leaf sheds water with its downward-curving hairs. I highly recommend it when surface water movement cannot be fully restricted.
 
It does bear mentioning that Salvinia can grow very rapidly. While S. cucullata is a “safe” species, others can become invasive in natural ecosystems. This is why the entire genus is restricted in some regions.
 

Water Lettuce & Red Root Floater

red root floater  azolla 1


On the other end of the spectrum, water lettuce and red root floater cannot tolerate even the slightest bit of excess water movement. I have observed water lettuce growing wild in blackwater lakes in the Amazon, where the contrast of the bright-green floating leaves against the deeply stained tannin water made quite an impression on me.
 
Water movement in this habitat was minimal, and shoals of tetras, cory cats, and juvenile cichlids swam in the blackwater beneath the roots of the water lettuce. I love to see its long roots dangle like feathers in the upper reaches of the water column—the gentler the water current, the longer the roots. I cannot imagine life without water lettuce! It is an ideal plant for sequestering excess nutrients and providing habitat for shy fish.
 
Red root floater (Phyllanthus fluitans) is another South American beauty, renowned for its bright-red foliage and short, dangling pink roots. Under good lighting conditions, red root floater will also form tiny white flowers that are extremely charming. For those desiring the deepest reds from their red root floaters, try restricting the nitrogen concentration in the tank.
 

Tiger Frogbit

tiger frogbit (1)


Tiger frogbit is a relatively rare floater in the aquarium scene and is believed to be a variant of the common South American frogbit (Limnobium laevigatum). Again, minimal water movement is critical for the plant’s best development.
 
The intensity of red striping also seems dependent on nitrogen concentration—less nitrogen equals more stripes. Tiger frogbit and red root floater are my go-to plants when I want to add a little interest or color to a small desktop pond-type aquascape. Just a sprinkling of a few leaves of one of these two species adds up to a lot of interest and completes the design.
 

Purple-Fringed Crystalwort


A rather obscure floating plant, and an interesting one to end on, is Ricciocarpos natans, the purple-fringed crystalwort. R. natans is a liverwort found around the globe in subpolar regions. What look like purple roots fringing the thalli (the green vegetative surface of the plant) are actually slender scales.
 
As easy as any floating plant to grow, as long as the slow water rule is honored, R. natans is my current floating plant crush. The purple scales and interesting fan-shaped thalli that dot the surface of the aquarium quickly develop into charming colonies. The scales keep the individual thalli perfectly spaced from one another, creating a cool mosaic effect. Though purple-fringed crystalwort is relatively rare in the commercial aquarium trade, I seem to always have some extra growing in my aquascapes.
 

Functional Beauty


Gathering their CO2 from the air at the water surface, growing with just about any type of lighting, and sequestering the nitrogen to help outcompete algae, floating aquarium plants are as functional as they are beautiful. If you’d like to pay me a visit in Seattle, drop in to Aquarium Zen and say hello to my floaters!

 

 
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