Can Dying Aquarium Plants Kill Fish?

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This topic is a bit unusual because live plants are generally seen as vital to any aquatic environment.

Especially a closed one like an aquarium which lacks the perks of open environments with a far superior chemical balance and circulation.

Plants are pretty much necessary to control the levels of nitrates, oxygenate the environment, and provide your fish with shelter and, sometimes, food.

But live plants also come with various health risks for your aquatic life under certain circumstances.

So, let’s discuss those!

How Can Dying Plants Kill Your Fish?

The main way a dying plant kills your fish is via chemical degradation. Simply put, aquatic plants, like plants in general, don’t just die suddenly.

Rather, they die in stages, with leaves falling off here and there until the plant is no longer self-sustainable. And herein lies the problem.

The dead leaves will soon decompose on the substrate since they are organic matter. And all dead organic matter feeds the system’s bad bacteria, causing a spike in ammonia and nitrites.

A well-cycled tank will cope with this problem relatively easily, thanks to its healthy biofilm.

In short, you have 2 types of good bacteria in the tank: Nitrosomonas and Nitrobacter, which are vital to any closed aquatic system.

The first type turns ammonia into nitrites, and the second type turns nitrites into nitrates. The latter chemical is way less toxic than the first 2, so concentrations of 5 to 10 ppm are considered safe for your aquatic life.

The problem comes when the ammonia and nitrite influx is so great that the resulting nitrates spike beyond the acceptable parameters. Nitrate concentrations of up to 20 ppm or higher will affect your fish over time and even kill them.

The deaths will happen progressively and appear unrelated, causing you to miss the common denominator. This issue can become overwhelming in a heavily planted tank that typically requires more maintenance.

A sudden boost of ammonia could cause the fish to experience nitrate shock and nitrate poisoning, which can turn deadly less than 24 hours later.

To prevent this problem, you should always manage your dying plants regularly. Remove dead leaves and eliminate whole plants altogether if they’re beyond salvation.

Why are Your Aquarium Plants Dying?

Aquarium plants will sometimes begin to die for no apparent reason. At this point, further investigation is necessary because what’s killing your plants may also start killing your fish at some point.

The most common causes of death among aquarium plants include:

Nutrient Deficiency

Aquatic plants require a variety of nutrients to remain healthy in the long run. These include phosphorus, magnesium, iron, potassium, manganese, etc.

In most cases, nutrient deficiencies occur when using the wrong type of water during a water change.

RO/DI water types are sterile in the sense that they contain no toxic agents or additives that might hurt your tank life. The problem is that the sterilization process that made the water safe also stripped it of all its micro and macronutrients.

So, using the water during a water change will deprive the environment of the nutrients that plants need to thrive.

Fortunately, your plants will display gradual symptoms of nutrient deficiency, allowing you to identify the problem in time and look for a solution.

Poor Photosynthesis

Plants require access to sunlight to perform adequate photosynthesis. Without that, they cannot extract nutrients from their environment, starve, and begin to die as a result.

You should provide your aquarium plants with at least 8 hours of sunlight daily to make sure they thrive.

Unfortunately, small mistakes often come with the most severe consequences.

Some of these include:

  • Surface floating plants – These often come with a powerful visual punch, creating a more natural-looking environment. The problem is that surface-floating plants keep sunlight from reaching the tank’s deeper layers. So, submerged plants will suffer the consequences.
  • Improper tank placementPlacing the tank in a room with poor access to sunlight is another issue for obvious reasons.
  • Algae overgrowth – This is a peculiar one but worthy of mentioning. Algae are normal in any tank, and they shouldn’t cause problems for the most part. If anything, they will serve as food for your fish. The problem is that algae spread everywhere and will cover every surface, including the plants. This will prevent the plant from getting access to sunlight and hinders its capability to perform photosynthesis.

CO2 Deficiency

Plants require CO2 to breathe during the day as part of the photosynthesis process. If CO2 is lacking, the plant will experience hindered growth and will begin to die shortly.

You can tell that the plant lacks adequate CO2 if its leaves turn yellow and grow slower than they should or not at all.

At this point, CO2 injections may be necessary to rebalance the environment and allow the plants to recover.

Algae Bloom

It is said that algae don’t compete over the same nutrients as plants, but they actually do. In reality, while plants and algae can coexist, for the most part, they will compete over the same nutrients.

This will lead to problems if algae bloom and are unchecked. That’s because they will spread fast and take over the entire habitat, covering the tank’s walls, the plants and even spreading to the water’s surface.

The result is often devastating, as your tank plants will experience nutrient deficiencies and poor or no access to sunlight. This turns aquarium algae into certified killers under ideal circumstances.

Regular tank maintenance, weekly water changes, and manual algae removal are necessary to prevent the problem.

Fish Activity

This is a less impactful issue, but it’s worth mentioning either way. The problem generally occurs in aquariums with substrate-digging fish like cichlids, catfish, and other bottom-dwellers.

The larger, more powerful, and more active the fish is, the more likely it is for it to unearth the plant or break its roots.

What’s more curious is that the plant will often remain in place even after its roots have been cut off. You won’t be able to tell something’s wrong until you notice the plant slowly dying.

So, I suggest either avoiding aggressive and overly active bottom dwellers, avoiding rooted plants, or choosing sturdier plant species that can withstand the fish’s attacks.

Excess Nitrate Levels

Aquatic plants require nitrates to survive since they make up the plants’ main food source. The problem comes when the nitrate content in the water exceeds the plants’ physiological needs.

If the nitrate content is too high, the plant may experience signs of nitrate toxicity since it can no longer process all of it.

This will cause symptoms like leaf discoloration, hindered growth, and even large holes visible in the leaves. The plant will begin to die soon after.

You can avoid this problem by monitoring nitrate levels and performing regular water changes to keep the nitrate levels below the safe threshold.

How do You Know If Your Plants are Dying?

Plants will exhibit a variety of symptoms when in the process of dying.

These include:

  • Yellow or brown leaves
  • Hindered growth, below what that plant species should reflect
  • Brittle leaves or holes visible in the leaves, etc.

You should consider investigating the problem further if your plants display any of these symptoms.

They’re either experiencing nutritional deficiencies, or something else is at play like high nitrates, poor lighting, low CO2, etc.

Plants will recover with adequate support, provided that the issue isn’t too severe.

How to Prevent Rotting Plants From Killing Your Fish?

There are 3 primary strategies available to help you keep both your plants and your fish safe:

  • Trim the plants – Some plants grow fast, and they spread fast. This can lead to lighting conductivity through the environment and may cause the plant to experience nutrient deficiencies. This can happen if the plant has outgrown its environment, as many aquarium plants tend to do. As a result, the aquarium plant will begin to lose leaves and die, and we all know where that leads. Trimming the plant regularly, especially if it’s a fast grower, is essential to prevent that.
  • Discover the problem – If your plant shows signs of decaying, you have a problem on your hands. The good thing is that plants are generally resilient and will recover after addressing the issue. Verify the CO2 levels, check the nitrate concentration, and assess the lighting level and water mineral content for starters. This should help you identify the problem and understand how to fix it. Keep your plants safe and well-nourished, and they will serve the environment well.
  • Clean and remove – Plants may shed dead leaves without dying themselves. Remove the dead leaves as soon as you see them to prevent the dead matter from accumulating on the substrate. If the plant is simply dying and is beyond salvation, removing the plant from the tank altogether may be your only option.

As you can see, caring for your tank plants is caring for the fish.


Tank plants play vital roles in the ecosystem but can sometimes cause more harm than good.

It’s up to you to identify the moment when your plants have lived long enough to become the villains and act accordingly.

I hope today’s article will help you in this sense.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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