Guest Post By Jino S. T.

Cambomba Caroliniana – Number 10 of the 10 worst aquarium plants

The Worst Plants You Can Get for Your Aquarium: A Cautionary Guide

Table of Contents

Hygrophila polysperma (Indian Swampweed): The Fast-Growing Menace. 1

What Makes It Terrible. 2

The Legal Issue. 2

The Bottom Line. 2

Salvinia molesta (Giant Salvinia): The Surface Invader. 2

What Makes It Terrible. 2

Environmental Impact 3

The Bottom Line. 3

Hydrilla verticillata (Hydrilla): The Master of Aquatic Invasion. 3

What Makes It Terrible. 3

Environmental Impact 4

The Bottom Line. 4

Egeria densa (Brazilian Waterweed): The Nutrient Hoarder. 4

What Makes It Terrible. 4

Environmental Impact 5

The Bottom Line. 5

Pistia stratiotes (Water Lettuce): The Light Thief 5

What Makes It Terrible. 5

Environmental Impact 6

The Bottom Line. 6

Myriophyllum aquaticum (Parrot Feather): The Amphibious Aggressor. 6

What Makes It Terrible. 6

Environmental Impact 6

The Bottom Line. 7

Ceratophyllum demersum (Coontail): The Hidden Troublemaker. 7

What Makes It Terrible. 7

Environmental Impact 7

The Bottom Line. 8

Lemna minor (Duckweed): The Eternal Resident 8

What Makes It Terrible. 8

Environmental Impact 8

The Bottom Line. 8

Alternanthera philoxeroides (Alligator Weed): The Adaptable Invader. 9

What Makes It Terrible. 9

Environmental Impact 9

The Bottom Line. 9

Cabomba caroliniana (Carolina Fanwort): The Deceptive Filter Clogger. 9

What Makes It Terrible. 10

Environmental Impact 10

The Bottom Line. 10

Conclusion: Making Informed Choices for Your Aquarium.. 10

Picture this: You’re standing in front of your beautifully arranged aquarium, admiring the careful balance of fish, decorations, and plants you’ve cultivated over months. Then you notice something isn’t quite right. That innocent-looking plant you added last week has somehow quadrupled in size, choking out your other plants and clogging the filter. Your pristine aquascape is quickly becoming an underwater jungle, and not in a good way.

This scenario plays out more often than you might think in the aquarium hobby. While aquatic plants can transform a tank into a stunning underwater garden, some species are nothing short of aquatic menaces. These botanical troublemakers can rapidly overtake an aquarium, alter water chemistry, harm fish, and prove nearly impossible to eliminate once established.

The problem isn’t just aesthetic. Problematic aquarium plants can impact every aspect of your tank’s ecosystem. They can block essential light from reaching other plants, deplete vital nutrients, interfere with equipment functionality, and even alter oxygen levels. Some species are so invasive that they’re banned in certain regions, and for good reason – escaped aquarium plants cause millions of dollars in environmental damage to natural waterways each year.

What makes identifying these problematic plants particularly challenging is that many are still widely available in the aquarium trade. Some are even marketed as “beginner-friendly” or “oxygen-generating” species, despite their potential to become aggressive invaders. Others might appear manageable in store display tanks but reveal their true nature once established in home aquariums.

In this comprehensive guide, we’ll explore the ten most problematic plants you should never add to your aquarium. From the deceptively cute duckweed to the aggressively spreading Brazilian waterweed, we’ll examine why these plants earned their place on the “worst of” list and why even experienced aquarists avoid them.

Hygrophila polysperma (Indian Swampweed): The Fast-Growing Menace

If you’ve been in the aquarium hobby for a while, you’ve probably heard whispers about Indian Swampweed. While it looks harmless with its bright green leaves and compact growth, this plant has earned its reputation as one of the most problematic aquarium plants you can get.

What Makes It Terrible

In optimal aquarium conditions (which aren’t hard to achieve), this plant grows at a rate that is hard to believe. We’re talking about 2-2.5 cm of new growth every single day, with stems that can reach lengths of over 2 feet. But the growth rate isn’t even the worst part.

The plant has developed several highly effective strategies that make it a nightmare to control. Each node (the points where leaves meet the stem) can develop roots, and every single fragment, no matter how small, can develop into a new plant.

It grows both underwater and above water, even growing out of your tank if given the chance. The stems constantly produce side shoots, creating dense bushes that take over entire sections of your aquarium.

Perhaps most surprisingly, it can flower and produce viable seeds even when fully submerged, giving it yet another way to spread.

To give you a real sense of scale: a single 6-inch stem can turn into dozens of plants within a month. The plant doesn’t just grow upward – it spreads sideways, creates runner stems along the substrate, and sends shoots in every direction. Even in low-light conditions or with poor nutrients, it continues to grow, just at a slightly slower pace. Its ability to adapt to almost any water parameters or lighting conditions means there’s virtually no aquarium where it won’t thrive and eventually become a problem.

The Legal Issue

Here’s something most hobbyists don’t realize until it’s too late: Indian Swampweed is actually illegal in many countries, including the United States. It’s been classified as a federal noxious weed because of how easily it escapes into local waterways and causes environmental damage. In places like Florida and Texas, it’s already created significant problems in natural ecosystems.

The Bottom Line

While it might seem like an attractive, fast-growing plant for your aquarium, the combination of its aggressive growth, near-impossible removal, and illegal status in many areas makes Indian Swampweed a plant you should absolutely avoid. Trust me, there are plenty of other beautiful, fast-growing plants that won’t take over your tank or potentially get you in trouble with the law.

Salvinia molesta (Giant Salvinia): The Surface Invader

If you’re looking for a floating plant that’ll make you regret every life decision that led you to aquarium keeping, Giant Salvinia is your plant. This floating fern might look delicate and attractive, but it’s earned its spot on this list through sheer aggressive growth.

What Makes It Terrible

Salvinia molesta earns its reputation through unprecedented growth rates and reproductive capabilities that have been extensively studied due to its environmental impact. In optimal conditions (temperatures between 20-30°C), a single plant can multiply into an 8-foot-wide mat in just three months. A small population can double its biomass in as little as 3-4 days, leading to surface coverage that increases exponentially.

The plant’s structure makes it particularly problematic in any aquatic system. Each plant consists of pairs of floating leaves connected by a submerged leaf that functions like a root. The upper surface of the floating leaves is covered in complex, water-repellent hairs arranged in an egg-beater pattern. This unique adaptation helps the plant stay afloat even in turbulent water and makes it resistant to mechanical removal – water simply rolls off the leaves, keeping them buoyant even when pushed under the surface.

The reproductive process is remarkably efficient: as the plant grows, it forms chains of connected plants that can reach up to 1 foot in length. When these chains break apart, each segment becomes an independent plant capable of starting its own colony. In aquarium conditions, where nutrients are plentiful and there are no natural predators, this growth pattern quickly leads to complete surface coverage. Even more concerning is its ability to survive in less than ideal conditions – when nutrients are scarce, the plant simply produces smaller leaves but continues to multiply, making it nearly impossible to control through nutrient limitation.

Environmental Impact

Giant Salvinia isn’t just a problem in home aquariums – it’s considered one of the world’s worst aquatic weeds. In natural environments, it forms such dense mats that boats can’t move through waterways, fish can’t surface for air, and native plants die from lack of light. It’s become such a problem that scientists have had to introduce special weevils in some areas just to control it.

The Bottom Line

Giant Salvinia is more than just an aquarium nuisance – it’s a serious invasive species that can quickly turn your tank into a maintenance nightmare. Its rapid growth rate, ability to block light, and tendency to degrade water quality make it a plant that should stay far away from your aquarium. Even if you’re an experienced aquarist, the risks far outweigh any potential benefits.

Hydrilla verticillata (Hydrilla): The Master of Aquatic Invasion

You might have heard Hydrilla being called “the perfect weed” in aquarium circles. The nickname isn’t just for show – scientists consider it one of the most successful invasive plants on Earth, capable of transforming aquatic environments in ways that few other species can match.

What Makes It Terrible

Hydrilla’s remarkable adaptability begins in the substrate, where it employs a multi-layered survival strategy. The plant produces four distinct types of reproductive structures: subterranean tubers that can survive for several years, axillary turions (compact buds) along the stems, fragmented pieces that readily root, and seeds in rare cases. These tubers are particularly problematic – they can survive in the substrate for up to 4 years, and a single square meter can contain over 5,000 tubers.

The growth pattern of Hydrilla is exceptionally aggressive. Under optimal conditions, stems can grow up to 1 inch per day and reach lengths of up to 25 feet, branching extensively as they grow. The plant’s physiology is uniquely adapted to outcompete other species – it can photosynthesize efficiently at both high and low light levels and can grow in water depths ranging from a few inches to over 20 feet. What makes it even more formidable is its ability to grow in low CO2 conditions by using bicarbonates as a carbon source, and its capacity to thrive in a wide range of temperatures from 68°F to 86°F.

Perhaps most concerning is its ability to alter water chemistry and tank conditions. As Hydrilla grows, it forms dense mats that can contain up to 6,000 leaf-crowded stems per square meter. These mats significantly reduce water flow, trap sediment, and create areas of fluctuating pH and oxygen levels.

The plant can also survive in conditions that would kill most other aquatic plants – it can grow in as little as 1% of full sunlight and tolerate a wide range of nutrient levels, making it nearly impossible to control through environmental manipulation.

Environmental Impact

The impact of Hydrilla extends far beyond home aquariums. In the United States alone, millions of dollars are spent annually on control efforts. The plant has invaded waterways across five continents, forming such dense underwater forests that they interfere with hydroelectric power generation, block water flow in flood control canals, and eliminate native aquatic plant species. In Florida alone, managing Hydrilla costs approximately $14 million per year.

The Bottom Line

Despite its impressive oxygenating capabilities and initial appeal as a fast-growing, hardy aquarium plant, Hydrilla’s aggressive nature and multiple survival strategies make it one of the worst possible choices for a home aquarium. Its ability to persist through nearly any control method, combined with its potential environmental impact if it escapes, means this is one plant that should remain firmly on your “never buy” list.

Egeria densa (Brazilian Waterweed): The Nutrient Hoarder

Brazilian Waterweed might be marketed sometimes as a beneficial oxygenating plant, but its growth characteristics and survival strategies make it one of the most challenging aquarium plants to control. In many countries, its sale has been banned entirely due to documented impacts on aquatic ecosystems.

What Makes It Terrible

Egeria densa’s success comes from its highly efficient growth and nutrient uptake systems. Each stem can grow up to 6 cm (2.36 inches) per day in optimal conditions, with nodes spaced only 1-3 cm apart. At each node, the plant produces whorls of 4-6 leaves, creating extremely dense vegetation. These leaves contain specialized chloroplasts that can function at just 1% of full sunlight, allowing the plant to photosynthesize efficiently even when shaded by other plants.

The plant’s reproductive capabilities are equally impressive. While it rarely produces seeds in aquarium conditions, it compensates through aggressive vegetative reproduction. Each node can produce both roots and new stems, and fragments as small as 2.5 cm (1 inch) can develop into new plants. More concerning is its ability to modify its growth based on conditions. In high-nutrient environments, it creates shorter internodes and more lateral branches, leading to even denser growth. Research has shown that a single established stem can produce over 250 fragments per season.

Environmental Impact

In natural systems, Egeria densa forms such dense colonies that it can reduce water flow by up to 80%. The plant’s biomass can double every 15-20 days in summer conditions, leading to rapid ecosystem alterations. Studies in California waterways have documented cases where it reduced dissolved oxygen levels by up to 35% in dense stands, creating conditions that severely impact native fish populations.

The Bottom Line

While Egeria densa’s oxygenating capabilities are real, its aggressive growth patterns and fragmentation abilities make it unsuitable for most aquariums. The constant maintenance required, combined with its potential environmental impact, far outweigh any benefits it might provide as an oxygenating plant.

Pistia stratiotes (Water Lettuce): The Light Thief

What looks like floating heads of lettuce turns out to be one of the most problematic floating plants you can add to your aquarium. Water Lettuce has earned its spot on this list not through fast growth alone, but through its incredible ability to transform an aquarium’s conditions.

What Makes It Terrible

The numbers tell the story here – a single Water Lettuce plant can produce up to 15 new plants every month through runners. These aren’t tiny offspring either; each new plant quickly develops a rosette of thick, spongy leaves and an extensive root system that can reach depths of 20 inches. In warm, nutrient-rich aquarium water, this growth rate accelerates even further.

What makes Water Lettuce particularly troublesome is its light-blocking efficiency. The leaves form tight, overlapping rosettes that create nearly complete surface coverage. Scientific measurements have shown that a layer of Water Lettuce can block up to 99% of incoming light – meaning your carefully chosen aquarium plants below are essentially sitting in the dark. The dense root system compounds this problem by creating a curtain effect underwater, further reducing light penetration and interfering with water flow.

Environmental Impact

In natural waterways, Water Lettuce has caused such significant problems that it’s banned in many regions. When it escapes from aquariums and ponds, it forms dense mats that completely cover water surfaces, drastically reducing oxygen levels and causing fish kills. In places like Florida, millions of dollars are spent annually trying to control this plant in natural systems.

The Bottom Line

While Water Lettuce might seem like an attractive floating plant for your aquarium, its aggressive reproduction, light-blocking capabilities, and extensive root system make it a poor choice. Once established, you’ll find yourself removing plants constantly just to maintain some balance in your aquarium. Given its status as a prohibited species in many areas, it’s best to look for less aggressive floating plants.

Myriophyllum aquaticum (Parrot Feather): The Amphibious Aggressor

Most aquatic plants stick to either growing underwater or on the surface. Parrot Feather does both, and that’s just the beginning of why it’s such a problem. Originally introduced as an ornamental plant, it’s now considered one of the most difficult aquatic plants to control.

What Makes It Terrible

Parrot Feather’s success comes from its unique growth strategy. Underwater, it forms dense stands of feathery leaves that can grow up to 6 feet in length. But it doesn’t stop there – once it reaches the surface, it changes form completely. The emerged stems grow up to 1 foot above the water, developing thicker, waxy leaves that are nearly impossible to kill with traditional herbicides.

The plant’s growth rate is staggering. Studies have documented growth rates of up to 10 cm per week under good conditions. But what makes this truly problematic is its fragmentation ability – each node on the stem can develop into a new plant, and stems can have over 20 nodes each. Even more concerning is its seasonal adaptation – in winter, it drops its leaves and forms dense root crowns that can survive freezing temperatures, only to regrow vigorously when conditions improve.

Environmental Impact

Parrot Feather has earned its reputation as a major aquatic pest. In natural systems, it forms such dense mats that it traps sediment, alters water flow, and creates stagnant zones. The emerged growth provides perfect mosquito breeding habitat, leading to additional environmental and health concerns. Its ability to grow both in and above water makes it particularly difficult to control once established in natural waterways.

The Bottom Line

Despite its attractive feathery appearance, Parrot Feather’s aggressive growth pattern, multiple survival strategies, and potential environmental impact make it a terrible choice for aquariums. Its ability to quickly outgrow any space and potentially spread to local waterways means this is one plant that should stay on the banned list.

Ceratophyllum demersum (Coontail): The Hidden Troublemaker

Unlike some of the more infamous plants on this list, Coontail often flies under the radar. It’s still commonly sold in pet stores as an oxygenating plant, which makes its inclusion here particularly important. Many aquarists learn about its problematic nature only after it’s too late.

What Makes It Terrible

Coontail’s growth pattern makes it particularly difficult to manage. The plant doesn’t develop true roots – instead, it floats freely in the water column, developing modified leaves that can anchor to substrate or other plants. This rootless growth means it can literally grow anywhere in your aquarium, making it nearly impossible to contain to one area.

Under optimal conditions, documented growth rates show stems can elongate by up to 5 cm (2 inches) per day. The plant fragments extremely easily, with each piece as small as 2 cm (.79 inches) being capable of developing into a new plant. What makes this especially problematic is its growth structure – each stem develops numerous side branches, creating dense whorls of needle-like leaves. These whorls trap debris efficiently, leading to significant water quality issues if not constantly maintained.

The plant also has a unique chemical defense mechanism – it releases allelopathic substances that inhibit the growth of other aquatic plants. Research has shown these compounds can significantly reduce the growth rate of many common aquarium plants, giving Coontail an unfair advantage in competing for nutrients and space.

Environmental Impact

In natural systems, Coontail can form such dense populations that it alters water chemistry and flow patterns. Its ability to grow in low-light conditions and tolerate a wide range of water parameters has made it a successful invader in many parts of the world. While not as notorious as some other plants on this list, its impact on aquatic ecosystems can be just as severe.

The Bottom Line

Despite its common presence in the hobby and its effectiveness as an oxygenating plant, Coontail’s aggressive growth, allelopathic properties, and tendency to create maintenance issues make it a poor choice for most aquariums. There are many other oxygenating plants available that won’t take over your tank or suppress the growth of your other plants.

Lemna minor (Duckweed): The Eternal Resident

If you’ve been in the aquarium hobby for any length of time, you’ve probably heard the saying “Getting duckweed is a choice. Keeping it is not.” While this tiny floating plant might seem harmless, its reputation as an aquarium pest is well-earned through years of frustrating aquarists worldwide.

What Makes It Terrible

Duckweed’s success comes from its remarkably efficient reproductive strategy. Each plant is tiny – only 2-4 mm across – but they reproduce through budding, with a single plant capable of producing 17,500 offspring in just two weeks under optimal conditions. Scientific studies have shown their population can double every 24-48 hours when nutrients and light are abundant, which is exactly what most planted aquariums provide.

What makes control particularly difficult is the plant’s size and structure. Each Lemna minor plant consists of a single leaf (or frond) with a tiny root hanging below. Their small size means they can slip through most filters and collection nets. They can survive in surprisingly low light conditions and can even go dormant when conditions are poor, only to explode in population once conditions improve. Even more frustrating is their ability to stick to any surface they touch – equipment, plants, hardscape, and even fish, making complete removal nearly impossible.

Environmental Impact

In natural waterways, duckweed can form mats so dense they block all light penetration to lower water levels. While it’s not as destructive as some other plants on this list, its ability to rapidly colonize water surfaces has led to significant problems in many ecosystems. In some areas, it’s considered an indicator of excessive nutrient levels in waterways.

The Bottom Line

Duckweed might seem appealing as a nutrient sponge and fish food, but the maintenance headache isn’t worth it. The combination of explosive growth rates and near-impossible removal makes it one of the most persistent nuisance plants in the hobby. If you want a floating plant, there are many better options that won’t take over your entire tank.

Alternanthera philoxeroides (Alligator Weed): The Adaptable Invader

This emergent plant was originally introduced as an ornamental species, but its ability to thrive in both aquatic and terrestrial environments has made it one of the most problematic plants in the hobby.

What Makes It Terrible

Alligator Weed demonstrates remarkable adaptability that makes it particularly difficult to control. The plant grows as interwoven mats of hollow stems that can extend up to 60 cm (23 inches) above water and root at each node. Scientific studies have documented growth rates of up to 15 cm (6 inches) per week in summer conditions. These hollow stems act as flotation devices, allowing broken pieces to drift and establish new colonies.

The plant’s ability to switch between aquatic and terrestrial growth forms is particularly problematic. When growing submersed, it develops thinner, more delicate leaves, but once it reaches the surface, it produces thick, waxy leaves that are more resistant to control methods. Even more concerning is its root structure – the plant develops extensive underground rhizomes that can penetrate up to 50 cm into substrate, making complete removal extremely difficult.

Environmental Impact

Alligator Weed has caused significant problems in waterways across the world. Its dense growth can reduce water flow by up to 40%, leading to increased flooding risks and altered water chemistry. In Australia alone, management costs exceed $4 million annually. The plant’s ability to grow on land means it can spread beyond water bodies, invading agricultural areas and wetlands.

The Bottom Line

Alligator Weed’s combination of rapid growth, multiple survival strategies, and amphibious nature makes it extremely problematic in aquarium settings. Its status as a regulated weed in many countries should be enough warning to keep this plant out of your tank.

Cabomba caroliniana (Carolina Fanwort): The Deceptive Filter Clogger

Carolina Fanwort remains popular in the aquarium trade due to its delicate, fan-like leaves and perceived ease of care. This popularity persists despite extensive documentation of its invasive potential and maintenance challenges.

What Makes It Terrible

Carolina Fanwort’s problematic nature stems from its specialized growth patterns. Each stem can grow up to 2 cm (.78 inches) per day, reaching lengths of over 10 meters in optimal conditions. The plant’s fine, fan-shaped leaves are arranged in dense whorls around the stem, with each leaf divided into thread-like segments. These delicate segments are exceptionally efficient at trapping detritus and becoming entangled in filter intakes.

The plant employs multiple reproductive strategies that make it particularly persistent. It can regenerate from fragments as small as 1 cm (.39 inches), produces specialized winter buds (turions) that can remain dormant in substrate for months, and can even flower and produce seeds underwater. Research has shown that a single stem can generate over 5,000 viable fragments per year. In aquarium conditions, where temperatures are stable and nutrients plentiful, growth becomes nearly continuous.

Environmental Impact

Carolina Fanwort has proven highly invasive in natural systems across multiple continents. Its dense growth alters water flow patterns and can reduce dissolved oxygen levels by up to 40%. The plant is banned in several countries, including New Zealand and parts of Australia, where control efforts have cost millions. In the United States, several states have prohibited its sale due to documented impacts on native ecosystems.

The Bottom Line

Carolina Fanwort’s maintenance requirements and potential for escapement make it an irresponsible choice for home aquariums. The same characteristics that make it attractive – fast growth and dense foliage – ultimately create significant long-term problems for aquarium keepers.

Making Informed Choices for Your Aquarium

The ten plants we’ve examined share several concerning characteristics: explosive growth rates, multiple reproductive strategies, and the ability to drastically alter aquarium conditions. While their rapid growth and hardy nature might seem appealing, especially to beginners looking for “easy” plants, these same traits make them problematic in confined aquarium spaces.

More importantly, these plants represent a broader responsibility we have as aquarium keepers. Many of the worst aquatic plant invasions worldwide started with aquarium releases. The cost of managing these plants in natural waterways runs into millions of dollars annually, with some ecosystems permanently altered by their presence.

Fortunately, the aquarium hobby offers many alternatives that provide similar benefits without the risks. For oxygenating plants, consider species like Pogostemon stellatus or Rotala rotundifolia. If you’re looking for floating plants, Salvinia minima or Limnobium laevigatum (Amazon Frogbit) offer similar benefits with more manageable growth rates. For background plants, species like Hygrophila corymbosa or Vallisneria americana provide excellent options that remain controllable.

The key to successful aquascaping isn’t finding the fastest-growing plants, but rather selecting species that complement your aquarium’s ecosystem while remaining manageable for long-term maintenance. By making informed choices about the plants we keep, we can create beautiful, sustainable aquariums while protecting our waterways.