Amazon Frogbit – A Complete Care Guide

If you looked into easy-to-care-for floating plants, you may have come across Amazon Frogbit. While this plant is easy to care for, it is also fast-growing and can take over your aquarium. In this guide, I’ll go over everything you need to know so you can be successful (or keep it at bay, so it doesn’t take over). Let’s get started!

Key Takeaways

  • Amazon frogbit is an easy species of floating plant that can provide food and shelter to freshwater fish and invertebrates.
  • This plant is very prolific and can be used as a biological control over excess nutrients. However, uncontrolled growth can prove to be detrimental to natural aquatic systems.
  • Amazon frogbit can propagate through seed production or stem fragmentation with the potential to quadruple in quantity over a few weeks.

A Brief Overview Of Amazon Frogbit

Scientific NameLimnobium laevigatum
Common NamesAmazon frogbit, American frogbit, South American spongeplant Smooth frogbit, West Indian spongeplant
FamilyHydrocharitaceae
OriginCentral and South America
Skill LevelEasy
LightingModerate
Tank PlacementSurface of water
Flow RateLow
Temperature Range64 – 86°F
Height<0.5 inches above the water, 1+ inches below the water
pH Range6.0 – 7.5
Growth RateVery fast
Feed TypeWater column feeder
Co2 RequirementNo

Introduction

Many of the tropical freshwater fish that we know and love originate from the blackwater ecosystems of the Amazon Rainforest throughout the northern portions of South America. While these exciting and vibrant species usually take precedence in home aquarium systems, their less colorful backdrops are often forgotten.

It is easy to think about the Amazon River as a murky waterway at the base of a plethora of green foliage and wild animals, but underneath the surface, the diversity persists. Thousands of plant species originate from these river systems, which have made their way into the freshwater aquarium hobby over the years. One of the most prolific yet understated species is Limnobium laevigatum, most commonly known as Amazon frogbit.

Amazon frogbit is a perennial floating plant that can completely cover the surface of slow-moving freshwater ecosystems. As we’ll see, this can become problematic when introduced as an invasive species1.

Origin And Habitat

Though named Amazon frogbit, this plant has a very wide natural range that ventures north of South America and into Central America. Amazon frogbit has been documented in the following countries as a naturally-occurring species: Mexico, Brazil, Antigua, Cuba, Dominican Republic, Guadeloupe, Martinique, Montserrat, Puerto Rico, St. Lucia, Trinidad, Costa Rica, El Salvador, Guatemala, Nicaragua, Panama, French Guiana, Guyana, Suriname, Venezuela, Argentina, Chile, Paraguay, Uruguay, Colombia, Ecuador, and Peru; it has not yet been determined if Amazon frogbit is endemic to Chile.

This plant thrives in subtropical and tropical climates with nutrient-rich waterways and bright sunlight. It establishes itself on the surface of slow to moderate-moving freshwater ponds, lakes, rivers, and streams, usually along margins and coastlines.

When controlled, Amazon frogbit provides food and protection to many aquatic and terrestrial species.

Are They Invasive?

When not controlled, Amazon frogbit becomes a huge problem for ecosystems. This plant is incredibly fast-growing and adaptable, making it one of the most opportunistic invasive species of plant. Amazon frogbit has been listed as an invasive species in portions of Europe, Australia, Africa, and some areas of the Americas.

Amazon frogbit was believed to be introduced to other countries via its use as an ornamental plant and aquarium species.

While plenty of other plants are considered invasive, the Amazon frogbit is one of the most damaging. To understand the destruction it can bring to local ecosystems, we must first understand the roles plants play in their respective ecosystems.

Both terrestrial and aquatic plants have evolved to succeed in their given ecosystem. This involves fast growth rates, good immunity and adaptability, and efficient nutrient uptake. The problem lies in Amazon frogbit’s ability to excel in all of these categories.

How Fast Do they Grow?

In the right conditions, Amazon frogbit populations have been known to double in size over the course of a few days. Within weeks, this number can quadruple.

This extremely fast-growing plant can grow sexually through seed production or asexually through stem fragmentation. Many times, this plant takes advantage of both methods. When sunlight and nutrient needs are met, Amazon frogbit can quickly cover the entire surface of a lake or pond.

The Problem

Oxygen and other gases are introduced into and removed from the water column through surface agitation and photosynthesis; photosynthesis is the process by which plants use carbon dioxide and water to create food and oxygen. Surface agitation can be influenced by currents, tides, and winds, while photosynthesis is performed by aquatic life.

When Amazon frogbit covers the surface of an aquatic system, the exchange of oxygen and other gases minimizes. The life below that relies on oxygen to breathe, like fish, invertebrates, and amphibians, begin to experience oxygen depletion, which can bring lethargy and eventual death. But won’t other plants help make up the for the lack of oxygen through photosynthesis?

No. Once the surface of the water is covered, other plants struggle to receive adequate sunlight, which is necessary for the photosynthetic process. In the meantime, the life that dies and decomposes due to these changes and depletions starts to die and increases nutrient levels in the water, which can lead to even more Amazon frogbit growth.

As a result, many countries use local weed management agencies to control and eradicate non-native Amazon frogbit populations as soon as possible. To help prevent the spread of this invasive species, never introduce it to outdoor water systems and check with local government regulations.

Appearance

Though harmful to ecosystems, Amazon frogbit can make a beautiful addition to the planted aquarium setup when controlled. This plant is very similar in appearance to other floating plants, like duckweed (Lemna minor) and water hyacinth (Eichhornia crassipes).

Floating Amazon Frogbit

Amazon frogbit has a miniature lily pad-like appearance, with small circular discs that radiate from a singular nodule; on average, the main stem trails about two inches down into the water column. These light green discs usually stay under an inch in diameter and close to the water’s surface.

If lucky, your Amazon frogbit may produce flowers, which can encourage flower pollination in pond and lake ecosystems. If conditions are met, your Amazon frogbit may develop yellow or white flowers.

What Are Good Fish Tank Mates For This Plant?

Amazon frogbit is an extremely popular aquarium plant in the freshwater hobby due to its delicate appearance as a floating plant and the shade and protection it can provide to top-dwelling species.

Good Fish Tank Mates

Most fish will appreciate the coverage provided by Amazon frogbit. In fact, this plant has been successfully used in both tropical and coldwater aquarium setups!

The best Amazon frogbit plant tank mates are:

Livebearers will especially love this plant as both adults and fry can find refuge in the fine trailing hairs of the plant. Both juvenile and adult goldfish will also love Amazon frogbit plants for food–which can be very helpful for a goldfish enthusiast looking for a natural, fast-growing food alternative.

Fish Species To Avoid

Amazon frogbit can be kept in all freshwater planted tank setups. This even includes species with an appetite for greens, like goldfish and silver dollars, as this plant can quickly replace itself.

Another factor that will determine whether or not you can keep Amazon frogbit in your aquarium is the rate of flow. As we’ll see, this plant does not do well when the top of its bright green leaves are exposed to wetness, which can happen if they are pushed underneath the surface by a strong water current.

Feeding

Amazon frogbit does not need to be fertilized; extra fertilization isn’t usually recommended. This plant is very efficient at uptaking any and all nutrients available in the water column, and an additional influx can lead to exponential growth.

That being said, it is sometimes necessary to add fertilizers to an aquarium that has Amazon frogbit plants. This is because, most times, aquarium owners also keep other plant species. Since the Amazon frogbit is a heavy feeder, nutrients can become scarce for these other species. A delicate balance between fertilizer dosing and Amazon frogbit population control needs to be established for the individual fish tank.

Because these plants require a constant source of nutrients, adding them to already established aquariums with a relatively high bioload is recommended.

How To Control Their Growth

More important than trying to grow Amazon frogbit is keeping up with Amazon frogbit growth. These plants will quickly cover the entire surface of the aquarium water if left to grow.

The easiest way to control Amazon frogbit growth is by manually removing it. This can be done with a siphon, fishnet, or by hand. The removed plants should be securely disposed of to prevent the possibility of introducing them into local waterways.

If keeping other aquarium plants, then it may also be worthwhile to use an algaecide, like Seachem Flourish Excel. This product introduces bioavailable organic carbon into the water column, helping to prevent algae blooms through an increased plant growth rate. Instead of promoting growth, Seachem Flourish Excel has been known to stop Amazon frogbit growth and even cause it to melt. Sometimes, though, this can cause the plant to flourish instead.

Seachem Flourish

An easy to use entry level fertilizer for freshwater planted tanks. Readily available at most stores

Buy On Amazon

The next best way to control Amazon frogbit growth is to make sure it doesn’t get into the aquarium in the first place. Not many hobbyists intentionally buy this plant, though it tends to come into their systems as a hitchhiker through other plants or animals. Even if you only have one small leaf of an Amazon frogbit plant, it can quickly propagate into a thick mat.

Another helpful hint is that Amazon frogbit plants prefer warm and soft water. Keeping them in cooler and harder water reduces the growth rate.

Care

The biggest part of Amazon frogbit care is making sure that it doesn’t take over your tank. This freshwater plant can and will survive whatever you put it through, and it’s deemed nearly indestructible. While extremely hardy, there are some basic conditions that need to be met in the home aquarium.

Planted Tank Parameters

Amazon frogbit can survive in most water parameters. However, it fails to thrive in low-nutrient systems. These plants are heavy water column feeders that need a constant and rich supply of nutrients, namely nitrates.

This tropical species is native to Central and South America. It needs a tropical water temperature between 64 and 86°F. A water temperature above or below this range can cause growth to be stunted or stopped entirely. Similarly, pH should remain constant between 6.0 and 7.5.

Otherwise, Amazon frogbit is very forgiving of imperfect water parameters and is sometimes intentionally used to suck up toxic ammonia from the water column. Ideally, Amazon frogbit plants should be kept in water parameters of 0 ppm ammonia, 0 ppm nitrite, and <20 ppm nitrates; because of their high demand for nutrients, many hobbyists keep a much higher nitrate level than this.

Nitrates may be introduced into the water column naturally through increased numbers of fish and invertebrates or manually dosed through a dry or liquid fertilizer; root tabs will not feed Amazon frogbit since these plants uptake nutrients from the water column.

Planted Aquarium Lighting

Amazon frogbit is an easy floating aquarium plant but requires slightly higher lighting than most other beginner species.

Amazon frogbit does best when given moderate to high lighting. There is a delicate balance between strong light and the distance between the light and the plant; the floating plants need to get a lot of light, or else they turn brown, but not so much that they start to burn. In most cases, a 3 to 5 inch clearance between the surface of the water and the light is enough.

The photoperiod should be between about 7 to 10 hours long.

Filtration 

This floating aquatic plant is commonly used for biological filtration in aquariums that lack mechanical filtration. This is because it is very efficient at taking up nutrients, which can then be ultimately removed from the aquarium by removing the plants.

In general, Amazon frogbit prefers dirty water with lots of nutrients. The level of filtration should be geared towards how big the aquarium is and the amount of bioload entering the system. Amazon frogbit can be kept with a sponge, hang on the back, canister, or sump filtration as long as the water surface current doesn’t cause plants to submerge.

Flow

More important than filtration is water flow. This floating plant needs to stay floating and will not tolerate being submerged!

Good surface water agitation is important for gas exchange in the aquarium. However, Amazon frogbit will melt if its leaves stay wet for extended periods of time. An overly strong filter or powerhead can cause these plants to be pushed around the aquarium and become partially or evenly fully submerged. An overly strong current can also cause the trailing roots to get damaged.

In general, Amazon frogbit should stay wherever it is planted, though a slight current is possible to maintain. To help keep water flow low, return heads can be baffled with plastic or other media.

Controlling

Unlike other freshwater aquarium plants, Amazon frogbit doesn’t need to be trimmed or pruned. Instead, whole portions of the mat can be removed all at once.

Once established, Amazon frogbit grows in a mat on the surface of the water. Removal is easy by simply picking up the pieces you want to discard; remember to dispose of them in a secure way so that they are not released into local waterways. It should be noted that Amazon frogbit sticks to everything–including hands and arms–so removal can be messy (though not as messy as duckweed).

To help keep Amazon frogbit from taking over the total surface layer of the aquarium, plastic rings may be floated to contain the mat; a DIY solution is gluing air tubing together to create a ring that can float.

Can You Put Them In A Pond?

Amazon frogbit is an extremely popular ornamental pond plant that probably shouldn’t be. Amazon frogbit has been introduced to many tropical and subtropical regions of the world as an invasive species. Many times, this was the result of an introduction from an outdoor pond setting.

Amazon frogbit can cling to the legs of birds and other animals, making transportation easy and almost instantaneous. Runoff and flooding can also contribute to invasive establishments.

While the Amazon frogbit might seem like the perfect floating plant for ponds, its usage is a huge risk to immediate ecosystems.

How To Propagate

In the wild, Amazon frogbit reproduces through seed production and stem fragmentation. Amazon frogbit produces yellow or white flowers that pollinate and give way to seeds. In the aquarium, stem fragmentation is the more likely route for propagation.

Amazon frogbit mainly reproduces by sending out new plants along its stem. As the new plant develops, the stems separate from each other until they are fully independent. This can happen at a very high rate, with plants sending out several new plants at once.

If conditions are met, then Amazon frogbit will quickly begin to propagate on its own.

Health And Disease

It is pretty easy to tell a happy Amazon frogbit plant from an unhappy one. Healthy plants will be bright green with spongey leaves, while unhealthy plants will have faded to yellow colors, sometimes even fully transparent.

Common Health Issues And Treatment

Color is the main sign of poor health in Amazon frogbit. Reduced growth and propagation rate are another. Loss of color can be caused by a few factors, like lighting, moisture, or nutrients.

Amazon frogbit lives on the surface of the water, where light is the brightest. Though it seems like more light would lead to healthier plants, high lighting can lead to your leaves yellowing and burning. Too little light can also lead to brown, dead leaves.

These plants are also subject to changes in color if the tops of their leaves have been exposed to wetness or moisture. This can happen if water pushes the leaves underwater or an aquarium lid causes condensation on the leaves. Water flow can be reduced, or greater airflow can be introduced into the aquarium.

Lastly, the color of your Amazon frogbit will largely depend on nutrient levels. These are heavy feeders that need a lot of nutrients to stay healthy and to continue to propagate. If color decreases and propagation slows, make sure to test that there are available nutrients in the water column.

Final Thoughts

Amazon frogbit is an extremely easy and fast-growing freshwater plant that thrives in tropical and subtropical climates. This floating plant can provide food, shelter, and nutrient export to fish and invertebrates alike. Amazon frogbit can also be used in outdoor pond settings as long as its growth and spread are strictly regulated. Once established, this plant can quickly overrun systems and become invasive.

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